/src/git/merge-ort.c

Source
/*
 * "Ostensibly Recursive's Twin" merge strategy, or "ort" for short.  Meant
 * as a drop-in replacement for the "recursive" merge strategy, allowing one
 * to replace
 *
 *   git merge [-s recursive]
 *
 * with
 *
 *   git merge -s ort
 *
 * Note: git's parser allows the space between '-s' and its argument to be
 * missing.  (Should I have backronymed "ham", "alsa", "kip", "nap, "alvo",
 * "cale", "peedy", or "ins" instead of "ort"?)
 */

#define USE_THE_REPOSITORY_VARIABLE
#define DISABLE_SIGN_COMPARE_WARNINGS

#include "git-compat-util.h"
#include "merge-ort.h"

#include "alloc.h"
#include "advice.h"
#include "attr.h"
#include "cache-tree.h"
#include "commit.h"
#include "commit-reach.h"
#include "config.h"
#include "diff.h"
#include "diffcore.h"
#include "dir.h"
#include "environment.h"
#include "gettext.h"
#include "hex.h"
#include "entry.h"
#include "merge-ll.h"
#include "match-trees.h"
#include "mem-pool.h"
#include "object-file.h"
#include "object-name.h"
#include "odb.h"
#include "oid-array.h"
#include "path.h"
#include "promisor-remote.h"
#include "read-cache-ll.h"
#include "refs.h"
#include "revision.h"
#include "sparse-index.h"
#include "strmap.h"
#include "trace2.h"
#include "tree.h"
#include "unpack-trees.h"
#include "xdiff-interface.h"

/*
 * We technically need USE_THE_REPOSITORY_VARIABLE above for DEFAULT_ABBREV,
 * but do not want more uses of the_repository.  Prevent them.
 *
 * opt->repo is available; use it instead.
 */
#define the_repository DO_NOT_USE_THE_REPOSITORY

/*
 * We have many arrays of size 3.  Whenever we have such an array, the
 * indices refer to one of the sides of the three-way merge.  This is so
 * pervasive that the constants 0, 1, and 2 are used in many places in the
 * code (especially in arithmetic operations to find the other side's index
 * or to compute a relevant mask), but sometimes these enum names are used
 * to aid code clarity.
 *
 * See also 'filemask' and 'dirmask' in struct conflict_info; the "ith side"
 * referred to there is one of these three sides.
 */
enum merge_side {
  MERGE_BASE = 0,
  MERGE_SIDE1 = 1,
  MERGE_SIDE2 = 2
};

static unsigned RESULT_INITIALIZED = 0x1abe11ed; /* unlikely accidental value */

struct traversal_callback_data {
  unsigned long mask;
  unsigned long dirmask;
  struct name_entry names[3];
};

struct deferred_traversal_data {
  /*
   * possible_trivial_merges: directories to be explored only when needed
   *
   * possible_trivial_merges is a map of directory names to
   * dir_rename_mask.  When we detect that a directory is unchanged on
   * one side, we can sometimes resolve the directory without recursing
   * into it.  Renames are the only things that can prevent such an
   * optimization.  However, for rename sources:
   *   - If no parent directory needed directory rename detection, then
   *     no path under such a directory can be a relevant_source.
   * and for rename destinations:
   *   - If no cached rename has a target path under the directory AND
   *   - If there are no unpaired relevant_sources elsewhere in the
   *     repository
   * then we don't need any path under this directory for a rename
   * destination.  The only way to know the last item above is to defer
   * handling such directories until the end of collect_merge_info(),
   * in handle_deferred_entries().
   *
   * For each we store dir_rename_mask, since that's the only bit of
   * information we need, other than the path, to resume the recursive
   * traversal.
   */
  struct strintmap possible_trivial_merges;

  /*
   * trivial_merges_okay: if trivial directory merges are okay
   *
   * See possible_trivial_merges above.  The "no unpaired
   * relevant_sources elsewhere in the repository" is a single boolean
   * per merge side, which we store here.  Note that while 0 means no,
   * 1 only means "maybe" rather than "yes"; we optimistically set it
   * to 1 initially and only clear when we determine it is unsafe to
   * do trivial directory merges.
   */
  unsigned trivial_merges_okay;

  /*
   * target_dirs: ancestor directories of rename targets
   *
   * target_dirs contains all directory names that are an ancestor of
   * any rename destination.
   */
  struct strset target_dirs;
};

struct rename_info {
  /*
   * All variables that are arrays of size 3 correspond to data tracked
   * for the sides in enum merge_side.  Index 0 is almost always unused
   * because we often only need to track information for MERGE_SIDE1 and
   * MERGE_SIDE2 (MERGE_BASE can't have rename information since renames
   * are determined relative to what changed since the MERGE_BASE).
   */

  /*
   * pairs: pairing of filenames from diffcore_rename()
   */
  struct diff_queue_struct pairs[3];

  /*
   * dirs_removed: directories removed on a given side of history.
   *
   * The keys of dirs_removed[side] are the directories that were removed
   * on the given side of history.  The value of the strintmap for each
   * directory is a value from enum dir_rename_relevance.
   */
  struct strintmap dirs_removed[3];

  /*
   * dir_rename_count: tracking where parts of a directory were renamed to
   *
   * When files in a directory are renamed, they may not all go to the
   * same location.  Each strmap here tracks:
   *      old_dir => {new_dir => int}
   * That is, dir_rename_count[side] is a strmap to a strintmap.
   */
  struct strmap dir_rename_count[3];

  /*
   * dir_renames: computed directory renames
   *
   * This is a map of old_dir => new_dir and is derived in part from
   * dir_rename_count.
   */
  struct strmap dir_renames[3];

  /*
   * relevant_sources: deleted paths wanted in rename detection, and why
   *
   * relevant_sources is a set of deleted paths on each side of
   * history for which we need rename detection.  If a path is deleted
   * on one side of history, we need to detect if it is part of a
   * rename if either
   *    * the file is modified/deleted on the other side of history
   *    * we need to detect renames for an ancestor directory
   * If neither of those are true, we can skip rename detection for
   * that path.  The reason is stored as a value from enum
   * file_rename_relevance, as the reason can inform the algorithm in
   * diffcore_rename_extended().
   */
  struct strintmap relevant_sources[3];

  struct deferred_traversal_data deferred[3];

  /*
   * dir_rename_mask:
   *   0: optimization removing unmodified potential rename source okay
   *   2 or 4: optimization okay, but must check for files added to dir
   *   7: optimization forbidden; need rename source in case of dir rename
   */
  unsigned dir_rename_mask:3;

  /*
   * callback_data_*: supporting data structures for alternate traversal
   *
   * We sometimes need to be able to traverse through all the files
   * in a given tree before all immediate subdirectories within that
   * tree.  Since traverse_trees() doesn't do that naturally, we have
   * a traverse_trees_wrapper() that stores any immediate
   * subdirectories while traversing files, then traverses the
   * immediate subdirectories later.  These callback_data* variables
   * store the information for the subdirectories so that we can do
   * that traversal order.
   */
  struct traversal_callback_data *callback_data;
  int callback_data_nr, callback_data_alloc;
  char *callback_data_traverse_path;

  /*
   * merge_trees: trees passed to the merge algorithm for the merge
   *
   * merge_trees records the trees passed to the merge algorithm.  But,
   * this data also is stored in merge_result->priv.  If a sequence of
   * merges are being done (such as when cherry-picking or rebasing),
   * the next merge can look at this and re-use information from
   * previous merges under certain circumstances.
   *
   * See also all the cached_* variables.
   */
  struct tree *merge_trees[3];

  /*
   * cached_pairs_valid_side: which side's cached info can be reused
   *
   * See the description for merge_trees.  For repeated merges, at most
   * only one side's cached information can be used.  Valid values:
   *   MERGE_SIDE2: cached data from side2 can be reused
   *   MERGE_SIDE1: cached data from side1 can be reused
   *   0:           no cached data can be reused
   *   -1:          See redo_after_renames; both sides can be reused.
   */
  int cached_pairs_valid_side;

  /*
   * cached_pairs: Caching of renames and deletions.
   *
   * These are mappings recording renames and deletions of individual
   * files (not directories).  They are thus a map from an old
   * filename to either NULL (for deletions) or a new filename (for
   * renames).
   */
  struct strmap cached_pairs[3];

  /*
   * cached_target_names: just the destinations from cached_pairs
   *
   * We sometimes want a fast lookup to determine if a given filename
   * is one of the destinations in cached_pairs.  cached_target_names
   * is thus duplicative information, but it provides a fast lookup.
   */
  struct strset cached_target_names[3];

  /*
   * cached_irrelevant: Caching of rename_sources that aren't relevant.
   *
   * If we try to detect a rename for a source path and succeed, it's
   * part of a rename.  If we try to detect a rename for a source path
   * and fail, then it's a delete.  If we do not try to detect a rename
   * for a path, then we don't know if it's a rename or a delete.  If
   * merge-ort doesn't think the path is relevant, then we just won't
   * cache anything for that path.  But there's a slight problem in
   * that merge-ort can think a path is RELEVANT_LOCATION, but due to
   * commit 9bd342137e ("diffcore-rename: determine which
   * relevant_sources are no longer relevant", 2021-03-13),
   * diffcore-rename can downgrade the path to RELEVANT_NO_MORE.  To
   * avoid excessive calls to diffcore_rename_extended() we still need
   * to cache such paths, though we cannot record them as either
   * renames or deletes.  So we cache them here as a "turned out to be
   * irrelevant *for this commit*" as they are often also irrelevant
   * for subsequent commits, though we will have to do some extra
   * checking to see whether such paths become relevant for rename
   * detection when cherry-picking/rebasing subsequent commits.
   */
  struct strset cached_irrelevant[3];

  /*
   * redo_after_renames: optimization flag for "restarting" the merge
   *
   * Sometimes it pays to detect renames, cache them, and then
   * restart the merge operation from the beginning.  The reason for
   * this is that when we know where all the renames are, we know
   * whether a certain directory has any paths under it affected --
   * and if a directory is not affected then it permits us to do
   * trivial tree merging in more cases.  Doing trivial tree merging
   * prevents the need to run process_entry() on every path
   * underneath trees that can be trivially merged, and
   * process_entry() is more expensive than collect_merge_info() --
   * plus, the second collect_merge_info() will be much faster since
   * it doesn't have to recurse into the relevant trees.
   *
   * Values for this flag:
   *   0 = don't bother, not worth it (or conditions not yet checked)
   *   1 = conditions for optimization met, optimization worthwhile
   *   2 = we already did it (don't restart merge yet again)
   */
  unsigned redo_after_renames;

  /*
   * needed_limit: value needed for inexact rename detection to run
   *
   * If the current rename limit wasn't high enough for inexact
   * rename detection to run, this records the limit needed.  Otherwise,
   * this value remains 0.
   */
  int needed_limit;
};

struct merge_options_internal {
  /*
   * paths: primary data structure in all of merge ort.
   *
   * The keys of paths:
   *   * are full relative paths from the toplevel of the repository
   *     (e.g. "drivers/firmware/raspberrypi.c").
   *   * store all relevant paths in the repo, both directories and
   *     files (e.g. drivers, drivers/firmware would also be included)
   *   * these keys serve to intern *all* path strings, which allows us
   *     to do pointer comparisons on file & directory names instead of
   *     using strcmp; however, for this pointer-comparison optimization
   *     to work, any code path that independently computes a path needs
   *     to check for it existing in this strmap, and if so, point to
   *     the path in this strmap instead of their computed copy.  See
   *     the "reuse known pointer" comment in
   *     apply_directory_rename_modifications() for an example.
   *
   * The values of paths:
   *   * either a pointer to a merged_info, or a conflict_info struct
   *   * merged_info contains all relevant information for a
   *     non-conflicted entry.
   *   * conflict_info contains a merged_info, plus any additional
   *     information about a conflict such as the higher orders stages
   *     involved and the names of the paths those came from (handy
   *     once renames get involved).
   *   * a path may start "conflicted" (i.e. point to a conflict_info)
   *     and then a later step (e.g. three-way content merge) determines
   *     it can be cleanly merged, at which point it'll be marked clean
   *     and the algorithm will ignore any data outside the contained
   *     merged_info for that entry
   *   * If an entry remains conflicted, the merged_info portion of a
   *     conflict_info will later be filled with whatever version of
   *     the file should be placed in the working directory (e.g. an
   *     as-merged-as-possible variation that contains conflict markers).
   */
  struct strmap paths;

  /*
   * conflicted: a subset of keys->values from "paths"
   *
   * conflicted is basically an optimization between process_entries()
   * and record_conflicted_index_entries(); the latter could loop over
   * ALL the entries in paths AGAIN and look for the ones that are
   * still conflicted, but since process_entries() has to loop over
   * all of them, it saves the ones it couldn't resolve in this strmap
   * so that record_conflicted_index_entries() can iterate just the
   * relevant entries.
   */
  struct strmap conflicted;

  /*
   * pool: memory pool for fast allocation/deallocation
   *
   * We allocate room for lots of filenames and auxiliary data
   * structures in merge_options_internal, and it tends to all be
   * freed together too.  Using a memory pool for these provides a
   * nice speedup.
   */
  struct mem_pool pool;

  /*
   * conflicts: logical conflicts and messages stored by _primary_ path
   *
   * This is a map of pathnames (a subset of the keys in "paths" above)
   * to struct string_list, with each item's `util` containing a
   * `struct logical_conflict_info`. Note, though, that for each path,
   * it only stores the logical conflicts for which that path is the
   * primary path; the path might be part of additional conflicts.
   */
  struct strmap conflicts;

  /*
   * renames: various data relating to rename detection
   */
  struct rename_info renames;

  /*
   * attr_index: hacky minimal index used for renormalization
   *
   * renormalization code _requires_ an index, though it only needs to
   * find a .gitattributes file within the index.  So, when
   * renormalization is important, we create a special index with just
   * that one file.
   */
  struct index_state attr_index;

  /*
   * current_dir_name, toplevel_dir: temporary vars
   *
   * These are used in collect_merge_info_callback(), and will set the
   * various merged_info.directory_name for the various paths we get;
   * see documentation for that variable and the requirements placed on
   * that field.
   */
  const char *current_dir_name;
  const char *toplevel_dir;

  /* call_depth: recursion level counter for merging merge bases */
  int call_depth;

  /* field that holds submodule conflict information */
  struct string_list conflicted_submodules;
};

struct conflicted_submodule_item {
  char *abbrev;
  int flag;
};

static void conflicted_submodule_item_free(void *util, const char *str UNUSED)
{
  struct conflicted_submodule_item *item = util;

  free(item->abbrev);
  free(item);
}

struct version_info {
  struct object_id oid;
  unsigned short mode;
};

struct merged_info {
  /* if is_null, ignore result.  otherwise result has oid & mode */
  struct version_info result;
  unsigned is_null:1;

  /*
   * clean: whether the path in question is cleanly merged.
   *
   * see conflict_info.merged for more details.
   */
  unsigned clean:1;

  /*
   * basename_offset: offset of basename of path.
   *
   * perf optimization to avoid recomputing offset of final '/'
   * character in pathname (0 if no '/' in pathname).
   */
  size_t basename_offset;

   /*
    * directory_name: containing directory name.
    *
    * Note that we assume directory_name is constructed such that
    *    strcmp(dir1_name, dir2_name) == 0 iff dir1_name == dir2_name,
    * i.e. string equality is equivalent to pointer equality.  For this
    * to hold, we have to be careful setting directory_name.
    */
  const char *directory_name;
};

struct conflict_info {
  /*
   * merged: the version of the path that will be written to working tree
   *
   * WARNING: It is critical to check merged.clean and ensure it is 0
   * before reading any conflict_info fields outside of merged.
   * Allocated merge_info structs will always have clean set to 1.
   * Allocated conflict_info structs will have merged.clean set to 0
   * initially.  The merged.clean field is how we know if it is safe
   * to access other parts of conflict_info besides merged; if a
   * conflict_info's merged.clean is changed to 1, the rest of the
   * algorithm is not allowed to look at anything outside of the
   * merged member anymore.
   */
  struct merged_info merged;

  /* oids & modes from each of the three trees for this path */
  struct version_info stages[3];

  /* pathnames for each stage; may differ due to rename detection */
  const char *pathnames[3];

  /* Whether this path is/was involved in a directory/file conflict */
  unsigned df_conflict:1;

  /*
   * Whether this path is/was involved in a non-content conflict other
   * than a directory/file conflict (e.g. rename/rename, rename/delete,
   * file location based on possible directory rename).
   */
  unsigned path_conflict:1;

  /*
   * For filemask and dirmask, the ith bit corresponds to whether the
   * ith entry is a file (filemask) or a directory (dirmask).  Thus,
   * filemask & dirmask is always zero, and filemask | dirmask is at
   * most 7 but can be less when a path does not appear as either a
   * file or a directory on at least one side of history.
   *
   * Note that these masks are related to enum merge_side, as the ith
   * entry corresponds to side i.
   *
   * These values come from a traverse_trees() call; more info may be
   * found looking at tree-walk.h's struct traverse_info,
   * particularly the documentation above the "fn" member (note that
   * filemask = mask & ~dirmask from that documentation).
   */
  unsigned filemask:3;
  unsigned dirmask:3;

  /*
   * Optimization to track which stages match, to avoid the need to
   * recompute it in multiple steps. Either 0 or at least 2 bits are
   * set; if at least 2 bits are set, their corresponding stages match.
   */
  unsigned match_mask:3;
};

enum conflict_and_info_types {
  /* "Simple" conflicts and informational messages */
  INFO_AUTO_MERGING = 0,
  CONFLICT_CONTENTS,       /* text file that failed to merge */
  CONFLICT_BINARY,
  CONFLICT_FILE_DIRECTORY,
  CONFLICT_DISTINCT_MODES,
  CONFLICT_MODIFY_DELETE,

  /* Regular rename */
  CONFLICT_RENAME_RENAME,   /* same file renamed differently */
  CONFLICT_RENAME_COLLIDES, /* rename/add or two files renamed to 1 */
  CONFLICT_RENAME_DELETE,

  /* Basic directory rename */
  CONFLICT_DIR_RENAME_SUGGESTED,
  INFO_DIR_RENAME_APPLIED,

  /* Special directory rename cases */
  INFO_DIR_RENAME_SKIPPED_DUE_TO_RERENAME,
  CONFLICT_DIR_RENAME_FILE_IN_WAY,
  CONFLICT_DIR_RENAME_COLLISION,
  CONFLICT_DIR_RENAME_SPLIT,

  /* Basic submodule */
  INFO_SUBMODULE_FAST_FORWARDING,
  CONFLICT_SUBMODULE_FAILED_TO_MERGE,

  /* Special submodule cases broken out from FAILED_TO_MERGE */
  CONFLICT_SUBMODULE_FAILED_TO_MERGE_BUT_POSSIBLE_RESOLUTION,
  CONFLICT_SUBMODULE_NOT_INITIALIZED,
  CONFLICT_SUBMODULE_HISTORY_NOT_AVAILABLE,
  CONFLICT_SUBMODULE_MAY_HAVE_REWINDS,
  CONFLICT_SUBMODULE_NULL_MERGE_BASE,

  /* INSERT NEW ENTRIES HERE */

  /*
   * Keep this entry after all regular conflict and info types; only
   * errors (failures causing immediate abort of the merge) should
   * come after this.
   */
  NB_REGULAR_CONFLICT_TYPES,

  /*
   * Something is seriously wrong; cannot even perform merge;
   * Keep this group _last_ other than NB_TOTAL_TYPES
   */
  ERROR_SUBMODULE_CORRUPT,
  ERROR_THREEWAY_CONTENT_MERGE_FAILED,
  ERROR_OBJECT_WRITE_FAILED,
  ERROR_OBJECT_READ_FAILED,
  ERROR_OBJECT_NOT_A_BLOB,

  /* Keep this entry _last_ in the list */
  NB_TOTAL_TYPES,
};

/*
 * Short description of conflict type, relied upon by external tools.
 *
 * We can add more entries, but DO NOT change any of these strings.  Also,
 * please ensure the order matches what is used in conflict_info_and_types.
 */
static const char *type_short_descriptions[] = {
  /*** "Simple" conflicts and informational messages ***/
  [INFO_AUTO_MERGING] = "Auto-merging",
  [CONFLICT_CONTENTS] = "CONFLICT (contents)",
  [CONFLICT_BINARY] = "CONFLICT (binary)",
  [CONFLICT_FILE_DIRECTORY] = "CONFLICT (file/directory)",
  [CONFLICT_DISTINCT_MODES] = "CONFLICT (distinct modes)",
  [CONFLICT_MODIFY_DELETE] = "CONFLICT (modify/delete)",

  /*** Regular rename ***/
  [CONFLICT_RENAME_RENAME] = "CONFLICT (rename/rename)",
  [CONFLICT_RENAME_COLLIDES] = "CONFLICT (rename involved in collision)",
  [CONFLICT_RENAME_DELETE] = "CONFLICT (rename/delete)",

  /*** Basic directory rename ***/
  [CONFLICT_DIR_RENAME_SUGGESTED] =
    "CONFLICT (directory rename suggested)",
  [INFO_DIR_RENAME_APPLIED] = "Path updated due to directory rename",

  /*** Special directory rename cases ***/
  [INFO_DIR_RENAME_SKIPPED_DUE_TO_RERENAME] =
    "Directory rename skipped since directory was renamed on both sides",
  [CONFLICT_DIR_RENAME_FILE_IN_WAY] =
    "CONFLICT (file in way of directory rename)",
  [CONFLICT_DIR_RENAME_COLLISION] = "CONFLICT(directory rename collision)",
  [CONFLICT_DIR_RENAME_SPLIT] = "CONFLICT(directory rename unclear split)",

  /*** Basic submodule ***/
  [INFO_SUBMODULE_FAST_FORWARDING] = "Fast forwarding submodule",
  [CONFLICT_SUBMODULE_FAILED_TO_MERGE] = "CONFLICT (submodule)",

  /*** Special submodule cases broken out from FAILED_TO_MERGE ***/
  [CONFLICT_SUBMODULE_FAILED_TO_MERGE_BUT_POSSIBLE_RESOLUTION] =
    "CONFLICT (submodule with possible resolution)",
  [CONFLICT_SUBMODULE_NOT_INITIALIZED] =
    "CONFLICT (submodule not initialized)",
  [CONFLICT_SUBMODULE_HISTORY_NOT_AVAILABLE] =
    "CONFLICT (submodule history not available)",
  [CONFLICT_SUBMODULE_MAY_HAVE_REWINDS] =
    "CONFLICT (submodule may have rewinds)",
  [CONFLICT_SUBMODULE_NULL_MERGE_BASE] =
    "CONFLICT (submodule lacks merge base)",

  /* Something is seriously wrong; cannot even perform merge */
  [ERROR_SUBMODULE_CORRUPT] =
    "ERROR (submodule corrupt)",
  [ERROR_THREEWAY_CONTENT_MERGE_FAILED] =
    "ERROR (three-way content merge failed)",
  [ERROR_OBJECT_WRITE_FAILED] =
    "ERROR (object write failed)",
  [ERROR_OBJECT_READ_FAILED] =
    "ERROR (object read failed)",
  [ERROR_OBJECT_NOT_A_BLOB] =
    "ERROR (object is not a blob)",
};

struct logical_conflict_info {
  enum conflict_and_info_types type;
  struct strvec paths;
};

/*** Function Grouping: various utility functions ***/

/*
 * For the next three macros, see warning for conflict_info.merged.
 *
 * In each of the below, mi is a struct merged_info*, and ci was defined
 * as a struct conflict_info* (but we need to verify ci isn't actually
 * pointed at a struct merged_info*).
 *
 * INITIALIZE_CI: Assign ci to mi but only if it's safe; set to NULL otherwise.
 * VERIFY_CI: Ensure that something we assigned to a conflict_info* is one.
 * ASSIGN_AND_VERIFY_CI: Similar to VERIFY_CI but do assignment first.
 */
#define INITIALIZE_CI(ci, mi) do {                                           \
  (ci) = (!(mi) || (mi)->clean) ? NULL : (struct conflict_info *)(mi); \
} while (0)
#define VERIFY_CI(ci) assert(ci && !ci->merged.clean);
#define ASSIGN_AND_VERIFY_CI(ci, mi) do {    \
  (ci) = (struct conflict_info *)(mi);  \
  assert((ci) && !(mi)->clean);        \
} while (0)

static void free_strmap_strings(struct strmap *map)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;

  strmap_for_each_entry(map, &iter, entry) {
    free((char*)entry->key);
  }
}

static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
            int reinitialize)
{
  struct rename_info *renames = &opti->renames;
  int i;
  void (*strmap_clear_func)(struct strmap *, int) =
    reinitialize ? strmap_partial_clear : strmap_clear;
  void (*strintmap_clear_func)(struct strintmap *) =
    reinitialize ? strintmap_partial_clear : strintmap_clear;
  void (*strset_clear_func)(struct strset *) =
    reinitialize ? strset_partial_clear : strset_clear;

  strmap_clear_func(&opti->paths, 0);

  /*
   * All keys and values in opti->conflicted are a subset of those in
   * opti->paths.  We don't want to deallocate anything twice, so we
   * don't free the keys and we pass 0 for free_values.
   */
  strmap_clear_func(&opti->conflicted, 0);

  discard_index(&opti->attr_index);

  /* Free memory used by various renames maps */
  for (i = MERGE_SIDE1; i <= MERGE_SIDE2; ++i) {
    strintmap_clear_func(&renames->dirs_removed[i]);
    strmap_clear_func(&renames->dir_renames[i], 0);
    strintmap_clear_func(&renames->relevant_sources[i]);
    if (!reinitialize)
      assert(renames->cached_pairs_valid_side == 0);
    if (i != renames->cached_pairs_valid_side &&
        -1 != renames->cached_pairs_valid_side) {
      strset_clear_func(&renames->cached_target_names[i]);
      strmap_clear_func(&renames->cached_pairs[i], 1);
      strset_clear_func(&renames->cached_irrelevant[i]);
      partial_clear_dir_rename_count(&renames->dir_rename_count[i]);
      if (!reinitialize)
        strmap_clear(&renames->dir_rename_count[i], 1);
    }
  }
  for (i = MERGE_SIDE1; i <= MERGE_SIDE2; ++i) {
    strintmap_clear_func(&renames->deferred[i].possible_trivial_merges);
    strset_clear_func(&renames->deferred[i].target_dirs);
    renames->deferred[i].trivial_merges_okay = 1; /* 1 == maybe */
  }
  renames->cached_pairs_valid_side = 0;
  renames->dir_rename_mask = 0;

  if (!reinitialize) {
    struct hashmap_iter iter;
    struct strmap_entry *e;

    /* Release and free each strbuf found in output */
    strmap_for_each_entry(&opti->conflicts, &iter, e) {
      struct string_list *list = e->value;
      for (int i = 0; i < list->nr; i++) {
        struct logical_conflict_info *info =
          list->items[i].util;
        strvec_clear(&info->paths);
      }
      /*
       * While strictly speaking we don't need to
       * free(conflicts) here because we could pass
       * free_values=1 when calling strmap_clear() on
       * opti->conflicts, that would require strmap_clear
       * to do another strmap_for_each_entry() loop, so we
       * just free it while we're iterating anyway.
       */
      string_list_clear(list, 1);
      free(list);
    }
    strmap_clear(&opti->conflicts, 0);
  }

  mem_pool_discard(&opti->pool, 0);

  string_list_clear_func(&opti->conflicted_submodules,
          conflicted_submodule_item_free);

  /* Clean out callback_data as well. */
  FREE_AND_NULL(renames->callback_data);
  renames->callback_data_nr = renames->callback_data_alloc = 0;
}

static void format_commit(struct strbuf *sb,
        int indent,
        struct repository *repo,
        struct commit *commit)
{
  struct merge_remote_desc *desc;
  struct pretty_print_context ctx = {0};
  ctx.abbrev = DEFAULT_ABBREV;

  strbuf_addchars(sb, ' ', indent);
  desc = merge_remote_util(commit);
  if (desc) {
    strbuf_addf(sb, "virtual %s\n", desc->name);
    return;
  }

  repo_format_commit_message(repo, commit, "%h %s", sb, &ctx);
  strbuf_addch(sb, '\n');
}

__attribute__((format (printf, 8, 9)))
static void path_msg(struct merge_options *opt,
         enum conflict_and_info_types type,
         int omittable_hint, /* skippable under --remerge-diff */
         const char *primary_path,
         const char *other_path_1, /* may be NULL */
         const char *other_path_2, /* may be NULL */
         struct string_list *other_paths, /* may be NULL */
         const char *fmt, ...)
{
  va_list ap;
  struct string_list *path_conflicts;
  struct logical_conflict_info *info;
  struct strbuf buf = STRBUF_INIT;
  struct strbuf *dest;
  struct strbuf tmp = STRBUF_INIT;

  /* Sanity checks */
  ASSERT(omittable_hint ==
         (!starts_with(type_short_descriptions[type], "CONFLICT") &&
    !starts_with(type_short_descriptions[type], "ERROR")) ||
         type == CONFLICT_DIR_RENAME_SUGGESTED);
  if (opt->record_conflict_msgs_as_headers && omittable_hint)
    return; /* Do not record mere hints in headers */
  if (opt->priv->call_depth && opt->verbosity < 5)
    return; /* Ignore messages from inner merges */

  /* Ensure path_conflicts (ptr to array of logical_conflict) allocated */
  path_conflicts = strmap_get(&opt->priv->conflicts, primary_path);
  if (!path_conflicts) {
    path_conflicts = xmalloc(sizeof(*path_conflicts));
    string_list_init_dup(path_conflicts);
    strmap_put(&opt->priv->conflicts, primary_path, path_conflicts);
  }

  /* Add a logical_conflict at the end to store info from this call */
  info = xcalloc(1, sizeof(*info));
  info->type = type;
  strvec_init(&info->paths);

  /* Handle the list of paths */
  strvec_push(&info->paths, primary_path);
  if (other_path_1)
    strvec_push(&info->paths, other_path_1);
  if (other_path_2)
    strvec_push(&info->paths, other_path_2);
  if (other_paths)
    for (int i = 0; i < other_paths->nr; i++)
    strvec_push(&info->paths, other_paths->items[i].string);

  /* Handle message and its format, in normal case */
  dest = (opt->record_conflict_msgs_as_headers ? &tmp : &buf);

  va_start(ap, fmt);
  if (opt->priv->call_depth) {
    strbuf_addchars(dest, ' ', 2);
    strbuf_addstr(dest, "From inner merge:");
    strbuf_addchars(dest, ' ', opt->priv->call_depth * 2);
  }
  strbuf_vaddf(dest, fmt, ap);
  va_end(ap);

  /* Handle specialized formatting of message under --remerge-diff */
  if (opt->record_conflict_msgs_as_headers) {
    int i_sb = 0, i_tmp = 0;

    /* Start with the specified prefix */
    if (opt->msg_header_prefix)
      strbuf_addf(&buf, "%s ", opt->msg_header_prefix);

    /* Copy tmp to sb, adding spaces after newlines */
    strbuf_grow(&buf, buf.len + 2*tmp.len); /* more than sufficient */
    for (; i_tmp < tmp.len; i_tmp++, i_sb++) {
      /* Copy next character from tmp to sb */
      buf.buf[buf.len + i_sb] = tmp.buf[i_tmp];

      /* If we copied a newline, add a space */
      if (tmp.buf[i_tmp] == '\n')
        buf.buf[++i_sb] = ' ';
    }
    /* Update length and ensure it's NUL-terminated */
    buf.len += i_sb;
    buf.buf[buf.len] = '\0';

    strbuf_release(&tmp);
  }
  string_list_append_nodup(path_conflicts, strbuf_detach(&buf, NULL))
    ->util = info;
}

static struct diff_filespec *pool_alloc_filespec(struct mem_pool *pool,
             const char *path)
{
  /* Similar to alloc_filespec(), but allocate from pool and reuse path */
  struct diff_filespec *spec;

  spec = mem_pool_calloc(pool, 1, sizeof(*spec));
  spec->path = (char*)path; /* spec won't modify it */

  spec->count = 1;
  spec->is_binary = -1;
  return spec;
}

static struct diff_filepair *pool_diff_queue(struct mem_pool *pool,
               struct diff_queue_struct *queue,
               struct diff_filespec *one,
               struct diff_filespec *two)
{
  /* Same code as diff_queue(), except allocate from pool */
  struct diff_filepair *dp;

  dp = mem_pool_calloc(pool, 1, sizeof(*dp));
  dp->one = one;
  dp->two = two;
  if (queue)
    diff_q(queue, dp);
  return dp;
}

/* add a string to a strbuf, but converting "/" to "_" */
static void add_flattened_path(struct strbuf *out, const char *s)
{
  size_t i = out->len;
  strbuf_addstr(out, s);
  for (; i < out->len; i++)
    if (out->buf[i] == '/')
      out->buf[i] = '_';
}

static char *unique_path(struct merge_options *opt,
       const char *path,
       const char *branch)
{
  char *ret = NULL;
  struct strbuf newpath = STRBUF_INIT;
  int suffix = 0;
  size_t base_len;
  struct strmap *existing_paths = &opt->priv->paths;

  strbuf_addf(&newpath, "%s~", path);
  add_flattened_path(&newpath, branch);

  base_len = newpath.len;
  while (strmap_contains(existing_paths, newpath.buf)) {
    strbuf_setlen(&newpath, base_len);
    strbuf_addf(&newpath, "_%d", suffix++);
  }

  /* Track the new path in our memory pool */
  ret = mem_pool_alloc(&opt->priv->pool, newpath.len + 1);
  memcpy(ret, newpath.buf, newpath.len + 1);
  strbuf_release(&newpath);
  return ret;
}

/*** Function Grouping: functions related to collect_merge_info() ***/

static int traverse_trees_wrapper_callback(int n,
             unsigned long mask,
             unsigned long dirmask,
             struct name_entry *names,
             struct traverse_info *info)
{
  struct merge_options *opt = info->data;
  struct rename_info *renames = &opt->priv->renames;
  unsigned filemask = mask & ~dirmask;

  assert(n==3);

  if (!renames->callback_data_traverse_path)
    renames->callback_data_traverse_path = xstrdup(info->traverse_path);

  if (filemask && filemask == renames->dir_rename_mask)
    renames->dir_rename_mask = 0x07;

  ALLOC_GROW(renames->callback_data, renames->callback_data_nr + 1,
       renames->callback_data_alloc);
  renames->callback_data[renames->callback_data_nr].mask = mask;
  renames->callback_data[renames->callback_data_nr].dirmask = dirmask;
  COPY_ARRAY(renames->callback_data[renames->callback_data_nr].names,
       names, 3);
  renames->callback_data_nr++;

  return mask;
}

/*
 * Much like traverse_trees(), BUT:
 *   - read all the tree entries FIRST, saving them
 *   - note that the above step provides an opportunity to compute necessary
 *     additional details before the "real" traversal
 *   - loop through the saved entries and call the original callback on them
 */
static int traverse_trees_wrapper(struct index_state *istate,
          int n,
          struct tree_desc *t,
          struct traverse_info *info)
{
  int ret, i, old_offset;
  traverse_callback_t old_fn;
  char *old_callback_data_traverse_path;
  struct merge_options *opt = info->data;
  struct rename_info *renames = &opt->priv->renames;

  assert(renames->dir_rename_mask == 2 || renames->dir_rename_mask == 4);

  old_callback_data_traverse_path = renames->callback_data_traverse_path;
  old_fn = info->fn;
  old_offset = renames->callback_data_nr;

  renames->callback_data_traverse_path = NULL;
  info->fn = traverse_trees_wrapper_callback;
  ret = traverse_trees(istate, n, t, info);
  if (ret < 0)
    return ret;

  info->traverse_path = renames->callback_data_traverse_path;
  info->fn = old_fn;
  for (i = old_offset; i < renames->callback_data_nr; ++i) {
    info->fn(n,
       renames->callback_data[i].mask,
       renames->callback_data[i].dirmask,
       renames->callback_data[i].names,
       info);
  }

  renames->callback_data_nr = old_offset;
  free(renames->callback_data_traverse_path);
  renames->callback_data_traverse_path = old_callback_data_traverse_path;
  info->traverse_path = NULL;
  return 0;
}

static void setup_path_info(struct merge_options *opt,
          struct string_list_item *result,
          const char *current_dir_name,
          int current_dir_name_len,
          char *fullpath, /* we'll take over ownership */
          struct name_entry *names,
          struct name_entry *merged_version,
          unsigned is_null,     /* boolean */
          unsigned df_conflict, /* boolean */
          unsigned filemask,
          unsigned dirmask,
          int resolved          /* boolean */)
{
  /* result->util is void*, so mi is a convenience typed variable */
  struct merged_info *mi;

  assert(!is_null || resolved);
  assert(!df_conflict || !resolved); /* df_conflict implies !resolved */
  assert(resolved == (merged_version != NULL));

  mi = mem_pool_calloc(&opt->priv->pool, 1,
           resolved ? sizeof(struct merged_info) :
          sizeof(struct conflict_info));
  mi->directory_name = current_dir_name;
  mi->basename_offset = current_dir_name_len;
  mi->clean = !!resolved;
  if (resolved) {
    mi->result.mode = merged_version->mode;
    oidcpy(&mi->result.oid, &merged_version->oid);
    mi->is_null = !!is_null;
  } else {
    int i;
    struct conflict_info *ci;

    ASSIGN_AND_VERIFY_CI(ci, mi);
    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
      ci->pathnames[i] = fullpath;
      ci->stages[i].mode = names[i].mode;
      oidcpy(&ci->stages[i].oid, &names[i].oid);
    }
    ci->filemask = filemask;
    ci->dirmask = dirmask;
    ci->df_conflict = !!df_conflict;
    if (dirmask)
      /*
       * Assume is_null for now, but if we have entries
       * under the directory then when it is complete in
       * write_completed_directory() it'll update this.
       * Also, for D/F conflicts, we have to handle the
       * directory first, then clear this bit and process
       * the file to see how it is handled -- that occurs
       * near the top of process_entry().
       */
      mi->is_null = 1;
  }
  strmap_put(&opt->priv->paths, fullpath, mi);
  result->string = fullpath;
  result->util = mi;
}

static void add_pair(struct merge_options *opt,
         struct name_entry *names,
         const char *pathname,
         unsigned side,
         unsigned is_add /* if false, is_delete */,
         unsigned match_mask,
         unsigned dir_rename_mask)
{
  struct diff_filespec *one, *two;
  struct rename_info *renames = &opt->priv->renames;
  int names_idx = is_add ? side : 0;

  if (is_add) {
    assert(match_mask == 0 || match_mask == 6);
    if (strset_contains(&renames->cached_target_names[side],
            pathname))
      return;
  } else {
    unsigned content_relevant = (match_mask == 0);
    unsigned location_relevant = (dir_rename_mask == 0x07);

    assert(match_mask == 0 || match_mask == 3 || match_mask == 5);

    /*
     * If pathname is found in cached_irrelevant[side] due to
     * previous pick but for this commit content is relevant,
     * then we need to remove it from cached_irrelevant.
     */
    if (content_relevant)
      /* strset_remove is no-op if strset doesn't have key */
      strset_remove(&renames->cached_irrelevant[side],
              pathname);

    /*
     * We do not need to re-detect renames for paths that we already
     * know the pairing, i.e. for cached_pairs (or
     * cached_irrelevant).  However, handle_deferred_entries() needs
     * to loop over the union of keys from relevant_sources[side] and
     * cached_pairs[side], so for simplicity we set relevant_sources
     * for all the cached_pairs too and then strip them back out in
     * prune_cached_from_relevant() at the beginning of
     * detect_regular_renames().
     */
    if (content_relevant || location_relevant) {
      /* content_relevant trumps location_relevant */
      strintmap_set(&renames->relevant_sources[side], pathname,
              content_relevant ? RELEVANT_CONTENT : RELEVANT_LOCATION);
    }

    /*
     * Avoid creating pair if we've already cached rename results.
     * Note that we do this after setting relevant_sources[side]
     * as noted in the comment above.
     */
    if (strmap_contains(&renames->cached_pairs[side], pathname) ||
        strset_contains(&renames->cached_irrelevant[side], pathname))
      return;
  }

  one = pool_alloc_filespec(&opt->priv->pool, pathname);
  two = pool_alloc_filespec(&opt->priv->pool, pathname);
  fill_filespec(is_add ? two : one,
          &names[names_idx].oid, 1, names[names_idx].mode);
  pool_diff_queue(&opt->priv->pool, &renames->pairs[side], one, two);
}

static void collect_rename_info(struct merge_options *opt,
        struct name_entry *names,
        const char *dirname,
        const char *fullname,
        unsigned filemask,
        unsigned dirmask,
        unsigned match_mask)
{
  struct rename_info *renames = &opt->priv->renames;
  unsigned side;

  /*
   * Update dir_rename_mask (determines ignore-rename-source validity)
   *
   * dir_rename_mask helps us keep track of when directory rename
   * detection may be relevant.  Basically, whenever a directory is
   * removed on one side of history, and a file is added to that
   * directory on the other side of history, directory rename
   * detection is relevant (meaning we have to detect renames for all
   * files within that directory to deduce where the directory
   * moved).  Also, whenever a directory needs directory rename
   * detection, due to the "majority rules" choice for where to move
   * it (see t6423 testcase 1f), we also need to detect renames for
   * all files within subdirectories of that directory as well.
   *
   * Here we haven't looked at files within the directory yet, we are
   * just looking at the directory itself.  So, if we aren't yet in
   * a case where a parent directory needed directory rename detection
   * (i.e. dir_rename_mask != 0x07), and if the directory was removed
   * on one side of history, record the mask of the other side of
   * history in dir_rename_mask.
   */
  if (renames->dir_rename_mask != 0x07 &&
      (dirmask == 3 || dirmask == 5)) {
    /* simple sanity check */
    assert(renames->dir_rename_mask == 0 ||
           renames->dir_rename_mask == (dirmask & ~1));
    /* update dir_rename_mask; have it record mask of new side */
    renames->dir_rename_mask = (dirmask & ~1);
  }

  /* Update dirs_removed, as needed */
  if (dirmask == 1 || dirmask == 3 || dirmask == 5) {
    /* absent_mask = 0x07 - dirmask; sides = absent_mask/2 */
    unsigned sides = (0x07 - dirmask)/2;
    unsigned relevance = (renames->dir_rename_mask == 0x07) ?
          RELEVANT_FOR_ANCESTOR : NOT_RELEVANT;
    /*
     * Record relevance of this directory.  However, note that
     * when collect_merge_info_callback() recurses into this
     * directory and calls collect_rename_info() on paths
     * within that directory, if we find a path that was added
     * to this directory on the other side of history, we will
     * upgrade this value to RELEVANT_FOR_SELF; see below.
     */
    if (sides & 1)
      strintmap_set(&renames->dirs_removed[1], fullname,
              relevance);
    if (sides & 2)
      strintmap_set(&renames->dirs_removed[2], fullname,
              relevance);
  }

  /*
   * Here's the block that potentially upgrades to RELEVANT_FOR_SELF.
   * When we run across a file added to a directory.  In such a case,
   * find the directory of the file and upgrade its relevance.
   */
  if (renames->dir_rename_mask == 0x07 &&
      (filemask == 2 || filemask == 4)) {
    /*
     * Need directory rename for parent directory on other side
     * of history from added file.  Thus
     *    side = (~filemask & 0x06) >> 1
     * or
     *    side = 3 - (filemask/2).
     */
    unsigned side = 3 - (filemask >> 1);
    strintmap_set(&renames->dirs_removed[side], dirname,
            RELEVANT_FOR_SELF);
  }

  if (filemask == 0 || filemask == 7)
    return;

  for (side = MERGE_SIDE1; side <= MERGE_SIDE2; ++side) {
    unsigned side_mask = (1 << side);

    /* Check for deletion on side */
    if ((filemask & 1) && !(filemask & side_mask))
      add_pair(opt, names, fullname, side, 0 /* delete */,
         match_mask & filemask,
         renames->dir_rename_mask);

    /* Check for addition on side */
    if (!(filemask & 1) && (filemask & side_mask))
      add_pair(opt, names, fullname, side, 1 /* add */,
         match_mask & filemask,
         renames->dir_rename_mask);
  }
}

static int collect_merge_info_callback(int n,
               unsigned long mask,
               unsigned long dirmask,
               struct name_entry *names,
               struct traverse_info *info)
{
  /*
   * n is 3.  Always.
   * common ancestor (mbase) has mask 1, and stored in index 0 of names
   * head of side 1  (side1) has mask 2, and stored in index 1 of names
   * head of side 2  (side2) has mask 4, and stored in index 2 of names
   */
  struct merge_options *opt = info->data;
  struct merge_options_internal *opti = opt->priv;
  struct rename_info *renames = &opt->priv->renames;
  struct string_list_item pi;  /* Path Info */
  struct conflict_info *ci; /* typed alias to pi.util (which is void*) */
  struct name_entry *p;
  size_t len;
  char *fullpath;
  const char *dirname = opti->current_dir_name;
  unsigned prev_dir_rename_mask = renames->dir_rename_mask;
  unsigned filemask = mask & ~dirmask;
  unsigned match_mask = 0; /* will be updated below */
  unsigned mbase_null = !(mask & 1);
  unsigned side1_null = !(mask & 2);
  unsigned side2_null = !(mask & 4);
  unsigned side1_matches_mbase = (!side1_null && !mbase_null &&
          names[0].mode == names[1].mode &&
          oideq(&names[0].oid, &names[1].oid));
  unsigned side2_matches_mbase = (!side2_null && !mbase_null &&
          names[0].mode == names[2].mode &&
          oideq(&names[0].oid, &names[2].oid));
  unsigned sides_match = (!side1_null && !side2_null &&
        names[1].mode == names[2].mode &&
        oideq(&names[1].oid, &names[2].oid));

  /*
   * Note: When a path is a file on one side of history and a directory
   * in another, we have a directory/file conflict.  In such cases, if
   * the conflict doesn't resolve from renames and deletions, then we
   * always leave directories where they are and move files out of the
   * way.  Thus, while struct conflict_info has a df_conflict field to
   * track such conflicts, we ignore that field for any directories at
   * a path and only pay attention to it for files at the given path.
   * The fact that we leave directories were they are also means that
   * we do not need to worry about getting additional df_conflict
   * information propagated from parent directories down to children
   * (unlike, say traverse_trees_recursive() in unpack-trees.c, which
   * sets a newinfo.df_conflicts field specifically to propagate it).
   */
  unsigned df_conflict = (filemask != 0) && (dirmask != 0);

  /* n = 3 is a fundamental assumption. */
  if (n != 3)
    BUG("Called collect_merge_info_callback wrong");

  /*
   * A bunch of sanity checks verifying that traverse_trees() calls
   * us the way I expect.  Could just remove these at some point,
   * though maybe they are helpful to future code readers.
   */
  assert(mbase_null == is_null_oid(&names[0].oid));
  assert(side1_null == is_null_oid(&names[1].oid));
  assert(side2_null == is_null_oid(&names[2].oid));
  assert(!mbase_null || !side1_null || !side2_null);
  assert(mask > 0 && mask < 8);

  /* Determine match_mask */
  if (side1_matches_mbase)
    match_mask = (side2_matches_mbase ? 7 : 3);
  else if (side2_matches_mbase)
    match_mask = 5;
  else if (sides_match)
    match_mask = 6;

  /*
   * Get the name of the relevant filepath, which we'll pass to
   * setup_path_info() for tracking.
   */
  p = names;
  while (!p->mode)
    p++;
  len = traverse_path_len(info, p->pathlen);

  /* +1 in both of the following lines to include the NUL byte */
  fullpath = mem_pool_alloc(&opt->priv->pool, len + 1);
  make_traverse_path(fullpath, len + 1, info, p->path, p->pathlen);

  /*
   * If mbase, side1, and side2 all match, we can resolve early.  Even
   * if these are trees, there will be no renames or anything
   * underneath.
   */
  if (side1_matches_mbase && side2_matches_mbase) {
    /* mbase, side1, & side2 all match; use mbase as resolution */
    setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
        names, names+0, mbase_null, 0 /* df_conflict */,
        filemask, dirmask, 1 /* resolved */);
    return mask;
  }

  /*
   * If the sides match, and all three paths are present and are
   * files, then we can take either as the resolution.  We can't do
   * this with trees, because there may be rename sources from the
   * merge_base.
   */
  if (sides_match && filemask == 0x07) {
    /* use side1 (== side2) version as resolution */
    setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
        names, names+1, side1_null, 0,
        filemask, dirmask, 1);
    return mask;
  }

  /*
   * If side1 matches mbase and all three paths are present and are
   * files, then we can use side2 as the resolution.  We cannot
   * necessarily do so this for trees, because there may be rename
   * destinations within side2.
   */
  if (side1_matches_mbase && filemask == 0x07) {
    /* use side2 version as resolution */
    setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
        names, names+2, side2_null, 0,
        filemask, dirmask, 1);
    return mask;
  }

  /* Similar to above but swapping sides 1 and 2 */
  if (side2_matches_mbase && filemask == 0x07) {
    /* use side1 version as resolution */
    setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
        names, names+1, side1_null, 0,
        filemask, dirmask, 1);
    return mask;
  }

  /*
   * Sometimes we can tell that a source path need not be included in
   * rename detection -- namely, whenever either
   *    side1_matches_mbase && side2_null
   * or
   *    side2_matches_mbase && side1_null
   * However, we call collect_rename_info() even in those cases,
   * because exact renames are cheap and would let us remove both a
   * source and destination path.  We'll cull the unneeded sources
   * later.
   */
  collect_rename_info(opt, names, dirname, fullpath,
          filemask, dirmask, match_mask);

  /*
   * None of the special cases above matched, so we have a
   * provisional conflict.  (Rename detection might allow us to
   * unconflict some more cases, but that comes later so all we can
   * do now is record the different non-null file hashes.)
   */
  setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
      names, NULL, 0, df_conflict, filemask, dirmask, 0);

  ci = pi.util;
  VERIFY_CI(ci);
  ci->match_mask = match_mask;

  /* If dirmask, recurse into subdirectories */
  if (dirmask) {
    struct traverse_info newinfo;
    struct tree_desc t[3];
    void *buf[3] = {NULL, NULL, NULL};
    const char *original_dir_name;
    int i, ret, side;

    /*
     * Check for whether we can avoid recursing due to one side
     * matching the merge base.  The side that does NOT match is
     * the one that might have a rename destination we need.
     */
    assert(!side1_matches_mbase || !side2_matches_mbase);
    side = side1_matches_mbase ? MERGE_SIDE2 :
      side2_matches_mbase ? MERGE_SIDE1 : MERGE_BASE;
    if (filemask == 0 && (dirmask == 2 || dirmask == 4)) {
      /*
       * Also defer recursing into new directories; set up a
       * few variables to let us do so.
       */
      ci->match_mask = (7 - dirmask);
      side = dirmask / 2;
    }
    if (renames->dir_rename_mask != 0x07 &&
        side != MERGE_BASE &&
        renames->deferred[side].trivial_merges_okay &&
        !strset_contains(&renames->deferred[side].target_dirs,
             pi.string)) {
      strintmap_set(&renames->deferred[side].possible_trivial_merges,
              pi.string, renames->dir_rename_mask);
      renames->dir_rename_mask = prev_dir_rename_mask;
      return mask;
    }

    /* We need to recurse */
    ci->match_mask &= filemask;
    newinfo = *info;
    newinfo.prev = info;
    newinfo.name = p->path;
    newinfo.namelen = p->pathlen;
    newinfo.pathlen = st_add3(newinfo.pathlen, p->pathlen, 1);
    /*
     * If this directory we are about to recurse into cared about
     * its parent directory (the current directory) having a D/F
     * conflict, then we'd propagate the masks in this way:
     *    newinfo.df_conflicts |= (mask & ~dirmask);
     * But we don't worry about propagating D/F conflicts.  (See
     * comment near setting of local df_conflict variable near
     * the beginning of this function).
     */

    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
      if (i == 1 && side1_matches_mbase)
        t[1] = t[0];
      else if (i == 2 && side2_matches_mbase)
        t[2] = t[0];
      else if (i == 2 && sides_match)
        t[2] = t[1];
      else {
        const struct object_id *oid = NULL;
        if (dirmask & 1)
          oid = &names[i].oid;
        buf[i] = fill_tree_descriptor(opt->repo,
                    t + i, oid);
      }
      dirmask >>= 1;
    }

    original_dir_name = opti->current_dir_name;
    opti->current_dir_name = pi.string;
    if (renames->dir_rename_mask == 0 ||
        renames->dir_rename_mask == 0x07)
      ret = traverse_trees(NULL, 3, t, &newinfo);
    else
      ret = traverse_trees_wrapper(NULL, 3, t, &newinfo);
    opti->current_dir_name = original_dir_name;
    renames->dir_rename_mask = prev_dir_rename_mask;

    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++)
      free(buf[i]);

    if (ret < 0)
      return -1;
  }

  return mask;
}

static void resolve_trivial_directory_merge(struct conflict_info *ci, int side)
{
  VERIFY_CI(ci);
  assert((side == 1 && ci->match_mask == 5) ||
         (side == 2 && ci->match_mask == 3));

  /*
   * Since ci->stages[0] matches ci->stages[3-side], resolve merge in
   * favor of ci->stages[side].
   */
  oidcpy(&ci->merged.result.oid, &ci->stages[side].oid);
  ci->merged.result.mode = ci->stages[side].mode;
  ci->merged.is_null = is_null_oid(&ci->stages[side].oid);

  /*
   * Because we resolved in favor of "side", we are no longer
   * considering the paths which matched (i.e. had the same hash) any
   * more.  Strip the matching paths from both dirmask & filemask.
   * Another consequence of merging in favor of side is that we can no
   * longer have a directory/file conflict either..but there's a slight
   * nuance we consider before clearing it.
   *
   * In most cases, resolving in favor of the other side means there's
   * no conflict at all, but if we had a directory/file conflict to
   * start, and the directory is resolved away, the remaining file could
   * still be part of a rename.  If the remaining file is part of a
   * rename, then it may also be part of a rename conflict (e.g.
   * rename/delete or rename/rename(1to2)), so we can't
   * mark it as a clean merge if we started with a directory/file
   * conflict and still have a file left.
   *
   * In contrast, if we started with a directory/file conflict and
   * still have a directory left, no file under that directory can be
   * part of a rename, otherwise we would have had to recurse into the
   * directory and would have never ended up within
   * resolve_trivial_directory_merge() for that directory.
   */
  ci->dirmask &= (~ci->match_mask);
  ci->filemask &= (~ci->match_mask);
  assert(!ci->filemask || !ci->dirmask);
  ci->match_mask = 0;
  ci->merged.clean = !ci->df_conflict || ci->dirmask;
  ci->df_conflict = 0;
}

static int handle_deferred_entries(struct merge_options *opt,
           struct traverse_info *info)
{
  struct rename_info *renames = &opt->priv->renames;
  struct hashmap_iter iter;
  struct strmap_entry *entry;
  int side, ret = 0;
  int path_count_before, path_count_after = 0;

  path_count_before = strmap_get_size(&opt->priv->paths);
  for (side = MERGE_SIDE1; side <= MERGE_SIDE2; side++) {
    unsigned optimization_okay = 1;
    struct strintmap copy;

    /* Loop over the set of paths we need to know rename info for */
    strintmap_for_each_entry(&renames->relevant_sources[side],
           &iter, entry) {
      char *rename_target, *dir, *dir_marker;
      struct strmap_entry *e;

      /*
       * If we don't know delete/rename info for this path,
       * then we need to recurse into all trees to get all
       * adds to make sure we have it.
       */
      if (strset_contains(&renames->cached_irrelevant[side],
              entry->key))
        continue;
      e = strmap_get_entry(&renames->cached_pairs[side],
               entry->key);
      if (!e) {
        optimization_okay = 0;
        break;
      }

      /* If this is a delete, we have enough info already */
      rename_target = e->value;
      if (!rename_target)
        continue;

      /* If we already walked the rename target, we're good */
      if (strmap_contains(&opt->priv->paths, rename_target))
        continue;

      /*
       * Otherwise, we need to get a list of directories that
       * will need to be recursed into to get this
       * rename_target.
       */
      dir = xstrdup(rename_target);
      while ((dir_marker = strrchr(dir, '/'))) {
        *dir_marker = '\0';
        if (strset_contains(&renames->deferred[side].target_dirs,
                dir))
          break;
        strset_add(&renames->deferred[side].target_dirs,
             dir);
      }
      free(dir);
    }
    renames->deferred[side].trivial_merges_okay = optimization_okay;
    /*
     * We need to recurse into any directories in
     * possible_trivial_merges[side] found in target_dirs[side].
     * But when we recurse, we may need to queue up some of the
     * subdirectories for possible_trivial_merges[side].  Since
     * we can't safely iterate through a hashmap while also adding
     * entries, move the entries into 'copy', iterate over 'copy',
     * and then we'll also iterate anything added into
     * possible_trivial_merges[side] once this loop is done.
     */
    copy = renames->deferred[side].possible_trivial_merges;
    strintmap_init_with_options(&renames->deferred[side].possible_trivial_merges,
              0,
              &opt->priv->pool,
              0);
    strintmap_for_each_entry(&copy, &iter, entry) {
      const char *path = entry->key;
      unsigned dir_rename_mask = (intptr_t)entry->value;
      struct conflict_info *ci;
      unsigned dirmask;
      struct tree_desc t[3];
      void *buf[3] = {NULL,};
      int i;

      ci = strmap_get(&opt->priv->paths, path);
      VERIFY_CI(ci);
      dirmask = ci->dirmask;

      if (optimization_okay &&
          !strset_contains(&renames->deferred[side].target_dirs,
               path)) {
        resolve_trivial_directory_merge(ci, side);
        continue;
      }

      info->name = path;
      info->namelen = strlen(path);
      info->pathlen = info->namelen + 1;

      for (i = 0; i < 3; i++, dirmask >>= 1) {
        if (i == 1 && ci->match_mask == 3)
          t[1] = t[0];
        else if (i == 2 && ci->match_mask == 5)
          t[2] = t[0];
        else if (i == 2 && ci->match_mask == 6)
          t[2] = t[1];
        else {
          const struct object_id *oid = NULL;
          if (dirmask & 1)
            oid = &ci->stages[i].oid;
          buf[i] = fill_tree_descriptor(opt->repo,
                      t+i, oid);
        }
      }

      ci->match_mask &= ci->filemask;
      opt->priv->current_dir_name = path;
      renames->dir_rename_mask = dir_rename_mask;
      if (renames->dir_rename_mask == 0 ||
          renames->dir_rename_mask == 0x07)
        ret = traverse_trees(NULL, 3, t, info);
      else
        ret = traverse_trees_wrapper(NULL, 3, t, info);

      for (i = MERGE_BASE; i <= MERGE_SIDE2; i++)
        free(buf[i]);

      if (ret < 0)
        return ret;
    }
    strintmap_clear(&copy);
    strintmap_for_each_entry(&renames->deferred[side].possible_trivial_merges,
           &iter, entry) {
      const char *path = entry->key;
      struct conflict_info *ci;

      ci = strmap_get(&opt->priv->paths, path);
      VERIFY_CI(ci);

      ASSERT(renames->deferred[side].trivial_merges_okay &&
             !strset_contains(&renames->deferred[side].target_dirs,
            path));
      resolve_trivial_directory_merge(ci, side);
    }
    if (!optimization_okay || path_count_after)
      path_count_after = strmap_get_size(&opt->priv->paths);
  }
  if (path_count_after) {
    /*
     * The choice of wanted_factor here does not affect
     * correctness, only performance.  When the
     *    path_count_after / path_count_before
     * ratio is high, redoing after renames is a big
     * performance boost.  I suspect that redoing is a wash
     * somewhere near a value of 2, and below that redoing will
     * slow things down.  I applied a fudge factor and picked
     * 3; see the commit message when this was introduced for
     * back of the envelope calculations for this ratio.
     */
    const int wanted_factor = 3;

    /* We should only redo collect_merge_info one time */
    assert(renames->redo_after_renames == 0);

    if (path_count_after / path_count_before >= wanted_factor) {
      renames->redo_after_renames = 1;
      renames->cached_pairs_valid_side = -1;
    }
  } else if (renames->redo_after_renames == 2)
    renames->redo_after_renames = 0;
  return ret;
}

static int collect_merge_info(struct merge_options *opt,
            struct tree *merge_base,
            struct tree *side1,
            struct tree *side2)
{
  int ret;
  struct tree_desc t[3];
  struct traverse_info info;

  opt->priv->toplevel_dir = "";
  opt->priv->current_dir_name = opt->priv->toplevel_dir;
  setup_traverse_info(&info, opt->priv->toplevel_dir);
  info.fn = collect_merge_info_callback;
  info.data = opt;
  info.show_all_errors = 1;

  if (repo_parse_tree(opt->repo, merge_base) < 0 ||
      repo_parse_tree(opt->repo, side1) < 0 ||
      repo_parse_tree(opt->repo, side2) < 0)
    return -1;
  init_tree_desc(t + 0, &merge_base->object.oid,
           merge_base->buffer, merge_base->size);
  init_tree_desc(t + 1, &side1->object.oid, side1->buffer, side1->size);
  init_tree_desc(t + 2, &side2->object.oid, side2->buffer, side2->size);

  trace2_region_enter("merge", "traverse_trees", opt->repo);
  ret = traverse_trees(NULL, 3, t, &info);
  if (ret == 0)
    ret = handle_deferred_entries(opt, &info);
  trace2_region_leave("merge", "traverse_trees", opt->repo);

  return ret;
}

/*** Function Grouping: functions related to threeway content merges ***/

static int find_first_merges(struct repository *repo,
           const char *path,
           struct commit *a,
           struct commit *b,
           struct object_array *result)
{
  int i, j;
  struct object_array merges = OBJECT_ARRAY_INIT;
  struct commit *commit;
  int contains_another;

  char merged_revision[GIT_MAX_HEXSZ + 2];
  const char *rev_args[] = { "rev-list", "--merges", "--ancestry-path",
           "--all", merged_revision, NULL };
  struct rev_info revs;
  struct setup_revision_opt rev_opts;

  memset(result, 0, sizeof(struct object_array));
  memset(&rev_opts, 0, sizeof(rev_opts));

  /* get all revisions that merge commit a */
  xsnprintf(merged_revision, sizeof(merged_revision), "^%s",
      oid_to_hex(&a->object.oid));
  repo_init_revisions(repo, &revs, NULL);
  /* FIXME: can't handle linked worktrees in submodules yet */
  revs.single_worktree = path != NULL;
  setup_revisions(ARRAY_SIZE(rev_args)-1, rev_args, &revs, &rev_opts);

  /* save all revisions from the above list that contain b */
  if (prepare_revision_walk(&revs))
    die("revision walk setup failed");
  while ((commit = get_revision(&revs)) != NULL) {
    struct object *o = &(commit->object);
    int ret = repo_in_merge_bases(repo, b, commit);

    if (ret < 0) {
      object_array_clear(&merges);
      release_revisions(&revs);
      return ret;
    }
    if (ret > 0)
      add_object_array(o, NULL, &merges);
  }
  reset_revision_walk();

  /* Now we've got all merges that contain a and b. Prune all
   * merges that contain another found merge and save them in
   * result.
   */
  for (i = 0; i < merges.nr; i++) {
    struct commit *m1 = (struct commit *) merges.objects[i].item;

    contains_another = 0;
    for (j = 0; j < merges.nr; j++) {
      struct commit *m2 = (struct commit *) merges.objects[j].item;
      if (i != j) {
        int ret = repo_in_merge_bases(repo, m2, m1);
        if (ret < 0) {
          object_array_clear(&merges);
          release_revisions(&revs);
          return ret;
        }
        if (ret > 0) {
          contains_another = 1;
          break;
        }
      }
    }

    if (!contains_another)
      add_object_array(merges.objects[i].item, NULL, result);
  }

  object_array_clear(&merges);
  release_revisions(&revs);
  return result->nr;
}

static int merge_submodule(struct merge_options *opt,
         const char *path,
         const struct object_id *o,
         const struct object_id *a,
         const struct object_id *b,
         struct object_id *result)
{
  struct repository subrepo;
  struct strbuf sb = STRBUF_INIT;
  int ret = 0, ret2;
  struct commit *commit_o, *commit_a, *commit_b;
  int parent_count;
  struct object_array merges;

  int i;
  int search = !opt->priv->call_depth;
  int sub_not_initialized = 1;
  int sub_flag = CONFLICT_SUBMODULE_FAILED_TO_MERGE;

  /* store fallback answer in result in case we fail */
  oidcpy(result, opt->priv->call_depth ? o : a);

  /* we can not handle deletion conflicts */
  if (is_null_oid(a) || is_null_oid(b))
    BUG("submodule deleted on one side; this should be handled outside of merge_submodule()");

  if ((sub_not_initialized = repo_submodule_init(&subrepo,
    opt->repo, path, null_oid(opt->repo->hash_algo)))) {
    path_msg(opt, CONFLICT_SUBMODULE_NOT_INITIALIZED, 0,
       path, NULL, NULL, NULL,
       _("Failed to merge submodule %s (not checked out)"),
       path);
    sub_flag = CONFLICT_SUBMODULE_NOT_INITIALIZED;
    goto cleanup;
  }

  if (is_null_oid(o)) {
    path_msg(opt, CONFLICT_SUBMODULE_NULL_MERGE_BASE, 0,
       path, NULL, NULL, NULL,
       _("Failed to merge submodule %s (no merge base)"),
       path);
    goto cleanup;
  }

  if (!(commit_o = lookup_commit_reference(&subrepo, o)) ||
      !(commit_a = lookup_commit_reference(&subrepo, a)) ||
      !(commit_b = lookup_commit_reference(&subrepo, b))) {
    path_msg(opt, CONFLICT_SUBMODULE_HISTORY_NOT_AVAILABLE, 0,
       path, NULL, NULL, NULL,
       _("Failed to merge submodule %s (commits not present)"),
       path);
    sub_flag = CONFLICT_SUBMODULE_HISTORY_NOT_AVAILABLE;
    goto cleanup;
  }

  /* check whether both changes are forward */
  ret2 = repo_in_merge_bases(&subrepo, commit_o, commit_a);
  if (ret2 < 0) {
    path_msg(opt, ERROR_SUBMODULE_CORRUPT, 0,
       path, NULL, NULL, NULL,
       _("error: failed to merge submodule %s "
         "(repository corrupt)"),
       path);
    ret = -1;
    goto cleanup;
  }
  if (ret2 > 0)
    ret2 = repo_in_merge_bases(&subrepo, commit_o, commit_b);
  if (ret2 < 0) {
    path_msg(opt, ERROR_SUBMODULE_CORRUPT, 0,
       path, NULL, NULL, NULL,
       _("error: failed to merge submodule %s "
         "(repository corrupt)"),
       path);
    ret = -1;
    goto cleanup;
  }
  if (!ret2) {
    path_msg(opt, CONFLICT_SUBMODULE_MAY_HAVE_REWINDS, 0,
       path, NULL, NULL, NULL,
       _("Failed to merge submodule %s "
         "(commits don't follow merge-base)"),
       path);
    goto cleanup;
  }

  /* Case #1: a is contained in b or vice versa */
  ret2 = repo_in_merge_bases(&subrepo, commit_a, commit_b);
  if (ret2 < 0) {
    path_msg(opt, ERROR_SUBMODULE_CORRUPT, 0,
       path, NULL, NULL, NULL,
       _("error: failed to merge submodule %s "
         "(repository corrupt)"),
       path);
    ret = -1;
    goto cleanup;
  }
  if (ret2 > 0) {
    oidcpy(result, b);
    path_msg(opt, INFO_SUBMODULE_FAST_FORWARDING, 1,
       path, NULL, NULL, NULL,
       _("Note: Fast-forwarding submodule %s to %s"),
       path, oid_to_hex(b));
    ret = 1;
    goto cleanup;
  }
  ret2 = repo_in_merge_bases(&subrepo, commit_b, commit_a);
  if (ret2 < 0) {
    path_msg(opt, ERROR_SUBMODULE_CORRUPT, 0,
       path, NULL, NULL, NULL,
       _("error: failed to merge submodule %s "
         "(repository corrupt)"),
       path);
    ret = -1;
    goto cleanup;
  }
  if (ret2 > 0) {
    oidcpy(result, a);
    path_msg(opt, INFO_SUBMODULE_FAST_FORWARDING, 1,
       path, NULL, NULL, NULL,
       _("Note: Fast-forwarding submodule %s to %s"),
       path, oid_to_hex(a));
    ret = 1;
    goto cleanup;
  }

  /*
   * Case #2: There are one or more merges that contain a and b in
   * the submodule. If there is only one, then present it as a
   * suggestion to the user, but leave it marked unmerged so the
   * user needs to confirm the resolution.
   */

  /* Skip the search if makes no sense to the calling context.  */
  if (!search)
    goto cleanup;

  /* find commit which merges them */
  parent_count = find_first_merges(&subrepo, path, commit_a, commit_b,
           &merges);
  switch (parent_count) {
  case -1:
    path_msg(opt, ERROR_SUBMODULE_CORRUPT, 0,
       path, NULL, NULL, NULL,
       _("error: failed to merge submodule %s "
         "(repository corrupt)"),
       path);
    ret = -1;
    break;
  case 0:
    path_msg(opt, CONFLICT_SUBMODULE_FAILED_TO_MERGE, 0,
       path, NULL, NULL, NULL,
       _("Failed to merge submodule %s"), path);
    break;

  case 1:
    format_commit(&sb, 4, &subrepo,
            (struct commit *)merges.objects[0].item);
    path_msg(opt, CONFLICT_SUBMODULE_FAILED_TO_MERGE_BUT_POSSIBLE_RESOLUTION, 0,
       path, NULL, NULL, NULL,
       _("Failed to merge submodule %s, but a possible merge "
         "resolution exists: %s"),
       path, sb.buf);
    strbuf_release(&sb);
    break;
  default:
    for (i = 0; i < merges.nr; i++)
      format_commit(&sb, 4, &subrepo,
              (struct commit *)merges.objects[i].item);
    path_msg(opt, CONFLICT_SUBMODULE_FAILED_TO_MERGE_BUT_POSSIBLE_RESOLUTION, 0,
       path, NULL, NULL, NULL,
       _("Failed to merge submodule %s, but multiple "
         "possible merges exist:\n%s"), path, sb.buf);
    strbuf_release(&sb);
  }

  object_array_clear(&merges);
cleanup:
  if (!opt->priv->call_depth && !ret) {
    struct string_list *csub = &opt->priv->conflicted_submodules;
    struct conflicted_submodule_item *util;
    const char *abbrev;

    util = xmalloc(sizeof(*util));
    util->flag = sub_flag;
    util->abbrev = NULL;
    if (!sub_not_initialized) {
      abbrev = repo_find_unique_abbrev(&subrepo, b, DEFAULT_ABBREV);
      util->abbrev = xstrdup(abbrev);
    }
    string_list_append(csub, path)->util = util;
  }

  if (!sub_not_initialized)
    repo_clear(&subrepo);
  return ret;
}

static void initialize_attr_index(struct merge_options *opt)
{
  /*
   * The renormalize_buffer() functions require attributes, and
   * annoyingly those can only be read from the working tree or from
   * an index_state.  merge-ort doesn't have an index_state, so we
   * generate a fake one containing only attribute information.
   */
  struct merged_info *mi;
  struct index_state *attr_index = &opt->priv->attr_index;
  struct cache_entry *ce;

  attr_index->repo = opt->repo;
  attr_index->initialized = 1;

  if (!opt->renormalize)
    return;

  mi = strmap_get(&opt->priv->paths, GITATTRIBUTES_FILE);
  if (!mi)
    return;

  if (mi->clean) {
    int len = strlen(GITATTRIBUTES_FILE);
    ce = make_empty_cache_entry(attr_index, len);
    ce->ce_mode = create_ce_mode(mi->result.mode);
    ce->ce_flags = create_ce_flags(0);
    ce->ce_namelen = len;
    oidcpy(&ce->oid, &mi->result.oid);
    memcpy(ce->name, GITATTRIBUTES_FILE, len);
    add_index_entry(attr_index, ce,
        ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
    get_stream_filter(attr_index, GITATTRIBUTES_FILE, &ce->oid);
  } else {
    int stage, len;
    struct conflict_info *ci;

    ASSIGN_AND_VERIFY_CI(ci, mi);
    for (stage = 0; stage < 3; stage++) {
      unsigned stage_mask = (1 << stage);

      if (!(ci->filemask & stage_mask))
        continue;
      len = strlen(GITATTRIBUTES_FILE);
      ce = make_empty_cache_entry(attr_index, len);
      ce->ce_mode = create_ce_mode(ci->stages[stage].mode);
      ce->ce_flags = create_ce_flags(stage);
      ce->ce_namelen = len;
      oidcpy(&ce->oid, &ci->stages[stage].oid);
      memcpy(ce->name, GITATTRIBUTES_FILE, len);
      add_index_entry(attr_index, ce,
          ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
      get_stream_filter(attr_index, GITATTRIBUTES_FILE,
            &ce->oid);
    }
  }
}

static int merge_3way(struct merge_options *opt,
          const char *path,
          const struct object_id *o,
          const struct object_id *a,
          const struct object_id *b,
          const char *pathnames[3],
          const int extra_marker_size,
          mmbuffer_t *result_buf)
{
  mmfile_t orig, src1, src2;
  struct ll_merge_options ll_opts = LL_MERGE_OPTIONS_INIT;
  char *base, *name1, *name2;
  enum ll_merge_result merge_status;

  if (!opt->priv->attr_index.initialized)
    initialize_attr_index(opt);

  ll_opts.renormalize = opt->renormalize;
  ll_opts.extra_marker_size = extra_marker_size;
  ll_opts.xdl_opts = opt->xdl_opts;
  ll_opts.conflict_style = opt->conflict_style;

  if (opt->priv->call_depth) {
    ll_opts.virtual_ancestor = 1;
    ll_opts.variant = 0;
  } else {
    switch (opt->recursive_variant) {
    case MERGE_VARIANT_OURS:
      ll_opts.variant = XDL_MERGE_FAVOR_OURS;
      break;
    case MERGE_VARIANT_THEIRS:
      ll_opts.variant = XDL_MERGE_FAVOR_THEIRS;
      break;
    default:
      ll_opts.variant = 0;
      break;
    }
  }

  assert(pathnames[0] && pathnames[1] && pathnames[2] && opt->ancestor);
  if (pathnames[0] == pathnames[1] && pathnames[1] == pathnames[2]) {
    base  = mkpathdup("%s", opt->ancestor);
    name1 = mkpathdup("%s", opt->branch1);
    name2 = mkpathdup("%s", opt->branch2);
  } else {
    base  = mkpathdup("%s:%s", opt->ancestor, pathnames[0]);
    name1 = mkpathdup("%s:%s", opt->branch1,  pathnames[1]);
    name2 = mkpathdup("%s:%s", opt->branch2,  pathnames[2]);
  }

  read_mmblob(&orig, opt->repo->objects, o);
  read_mmblob(&src1, opt->repo->objects, a);
  read_mmblob(&src2, opt->repo->objects, b);

  merge_status = ll_merge(result_buf, path, &orig, base,
        &src1, name1, &src2, name2,
        &opt->priv->attr_index, &ll_opts);
  if (merge_status == LL_MERGE_BINARY_CONFLICT)
    path_msg(opt, CONFLICT_BINARY, 0,
       path, NULL, NULL, NULL,
       "warning: Cannot merge binary files: %s (%s vs. %s)",
       path, name1, name2);

  free(base);
  free(name1);
  free(name2);
  free(orig.ptr);
  free(src1.ptr);
  free(src2.ptr);
  return merge_status;
}

static int handle_content_merge(struct merge_options *opt,
        const char *path,
        const struct version_info *o,
        const struct version_info *a,
        const struct version_info *b,
        const char *pathnames[3],
        const int extra_marker_size,
        const int record_object,
        struct version_info *result)
{
  /*
   * path is the target location where we want to put the file, and
   * is used to determine any normalization rules in ll_merge.
   *
   * The normal case is that path and all entries in pathnames are
   * identical, though renames can affect which path we got one of
   * the three blobs to merge on various sides of history.
   *
   * extra_marker_size is the amount to extend conflict markers in
   * ll_merge; this is needed if we have content merges of content
   * merges, which happens for example with rename/rename(2to1) and
   * rename/add conflicts.
   */
  int clean = 1;

  /*
   * handle_content_merge() needs both files to be of the same type, i.e.
   * both files OR both submodules OR both symlinks.  Conflicting types
   * needs to be handled elsewhere.
   */
  assert((S_IFMT & a->mode) == (S_IFMT & b->mode));

  /* Merge modes */
  if (a->mode == b->mode || a->mode == o->mode)
    result->mode = b->mode;
  else {
    /* must be the 100644/100755 case */
    assert(S_ISREG(a->mode));
    result->mode = a->mode;
    clean = (b->mode == o->mode);
    /*
     * FIXME: If opt->priv->call_depth && !clean, then we really
     * should not make result->mode match either a->mode or
     * b->mode; that causes t6416 "check conflicting mode for
     * regular file" to fail.  It would be best to use some other
     * mode, but we'll confuse all kinds of stuff if we use one
     * where S_ISREG(result->mode) isn't true, and if we use
     * something like 0100666, then tree-walk.c's calls to
     * canon_mode() will just normalize that to 100644 for us and
     * thus not solve anything.
     *
     * Figure out if there's some kind of way we can work around
     * this...
     */
  }

  /*
   * Trivial oid merge.
   *
   * Note: While one might assume that the next four lines would
   * be unnecessary due to the fact that match_mask is often
   * setup and already handled, renames don't always take care
   * of that.
   */
  if (oideq(&a->oid, &b->oid) || oideq(&a->oid, &o->oid))
    oidcpy(&result->oid, &b->oid);
  else if (oideq(&b->oid, &o->oid))
    oidcpy(&result->oid, &a->oid);

  /* Remaining rules depend on file vs. submodule vs. symlink. */
  else if (S_ISREG(a->mode)) {
    mmbuffer_t result_buf;
    int ret = 0, merge_status;
    int two_way;

    /*
     * If 'o' is different type, treat it as null so we do a
     * two-way merge.
     */
    two_way = ((S_IFMT & o->mode) != (S_IFMT & a->mode));

    merge_status = merge_3way(opt, path,
            two_way ? null_oid(opt->repo->hash_algo) : &o->oid,
            &a->oid, &b->oid,
            pathnames, extra_marker_size,
            &result_buf);

    if ((merge_status < 0) || !result_buf.ptr) {
      path_msg(opt, ERROR_THREEWAY_CONTENT_MERGE_FAILED, 0,
         pathnames[0], pathnames[1], pathnames[2], NULL,
         _("error: failed to execute internal merge for %s"),
         path);
      ret = -1;
    }

    if (!ret && record_object &&
        odb_write_object(opt->repo->objects, result_buf.ptr, result_buf.size,
             OBJ_BLOB, &result->oid)) {
      path_msg(opt, ERROR_OBJECT_WRITE_FAILED, 0,
         pathnames[0], pathnames[1], pathnames[2], NULL,
         _("error: unable to add %s to database"), path);
      ret = -1;
    }
    free(result_buf.ptr);

    if (ret)
      return -1;
    if (merge_status > 0)
      clean = 0;
    path_msg(opt, INFO_AUTO_MERGING, 1, path, NULL, NULL, NULL,
       _("Auto-merging %s"), path);
  } else if (S_ISGITLINK(a->mode)) {
    int two_way = ((S_IFMT & o->mode) != (S_IFMT & a->mode));
    clean = merge_submodule(opt, pathnames[0],
          two_way ? null_oid(opt->repo->hash_algo) : &o->oid,
          &a->oid, &b->oid, &result->oid);
    if (clean < 0)
      return -1;
    if (opt->priv->call_depth && two_way && !clean) {
      result->mode = o->mode;
      oidcpy(&result->oid, &o->oid);
    }
  } else if (S_ISLNK(a->mode)) {
    if (opt->priv->call_depth) {
      clean = 0;
      result->mode = o->mode;
      oidcpy(&result->oid, &o->oid);
    } else {
      switch (opt->recursive_variant) {
      case MERGE_VARIANT_NORMAL:
        clean = 0;
        oidcpy(&result->oid, &a->oid);
        break;
      case MERGE_VARIANT_OURS:
        oidcpy(&result->oid, &a->oid);
        break;
      case MERGE_VARIANT_THEIRS:
        oidcpy(&result->oid, &b->oid);
        break;
      }
    }
  } else
    BUG("unsupported object type in the tree: %06o for %s",
        a->mode, path);

  return clean;
}

/*** Function Grouping: functions related to detect_and_process_renames(), ***
 *** which are split into directory and regular rename detection sections. ***/

/*** Function Grouping: functions related to directory rename detection ***/

struct collision_info {
  struct string_list source_files;
  unsigned reported_already:1;
};

/*
 * Return a new string that replaces the beginning portion (which matches
 * rename_info->key), with rename_info->util.new_dir.  In perl-speak:
 *   new_path_name = (old_path =~ s/rename_info->key/rename_info->value/);
 * NOTE:
 *   Caller must ensure that old_path starts with rename_info->key + '/'.
 */
static char *apply_dir_rename(struct strmap_entry *rename_info,
            const char *old_path)
{
  struct strbuf new_path = STRBUF_INIT;
  const char *old_dir = rename_info->key;
  const char *new_dir = rename_info->value;
  int oldlen, newlen, new_dir_len;

  oldlen = strlen(old_dir);
  if (*new_dir == '\0')
    /*
     * If someone renamed/merged a subdirectory into the root
     * directory (e.g. 'some/subdir' -> ''), then we want to
     * avoid returning
     *     '' + '/filename'
     * as the rename; we need to make old_path + oldlen advance
     * past the '/' character.
     */
    oldlen++;
  new_dir_len = strlen(new_dir);
  newlen = new_dir_len + (strlen(old_path) - oldlen) + 1;
  strbuf_grow(&new_path, newlen);
  strbuf_add(&new_path, new_dir, new_dir_len);
  strbuf_addstr(&new_path, &old_path[oldlen]);

  return strbuf_detach(&new_path, NULL);
}

static int path_in_way(struct strmap *paths,
           const char *path,
           unsigned side_mask,
           struct diff_filepair *p)
{
  struct merged_info *mi = strmap_get(paths, path);
  struct conflict_info *ci;
  if (!mi)
    return 0;
  INITIALIZE_CI(ci, mi);
  return mi->clean || (side_mask & (ci->filemask | ci->dirmask))
    /* See testcases 12[npq] of t6423 for this next condition */
       || ((ci->filemask & 0x01) &&
           strcmp(p->one->path, path));
}

/*
 * See if there is a directory rename for path, and if there are any file
 * level conflicts on the given side for the renamed location.  If there is
 * a rename and there are no conflicts, return the new name.  Otherwise,
 * return NULL.
 */
static char *handle_path_level_conflicts(struct merge_options *opt,
           const char *path,
           unsigned side_index,
           struct diff_filepair *p,
           struct strmap_entry *rename_info,
           struct strmap *collisions)
{
  char *new_path = NULL;
  struct collision_info *c_info;
  int clean = 1;
  struct strbuf collision_paths = STRBUF_INIT;

  /*
   * entry has the mapping of old directory name to new directory name
   * that we want to apply to path.
   */
  new_path = apply_dir_rename(rename_info, path);
  if (!new_path)
    BUG("Failed to apply directory rename!");

  /*
   * The caller needs to have ensured that it has pre-populated
   * collisions with all paths that map to new_path.  Do a quick check
   * to ensure that's the case.
   */
  c_info = strmap_get(collisions, new_path);
  if (!c_info)
    BUG("c_info is NULL");

  /*
   * Check for one-sided add/add/.../add conflicts, i.e.
   * where implicit renames from the other side doing
   * directory rename(s) can affect this side of history
   * to put multiple paths into the same location.  Warn
   * and bail on directory renames for such paths.
   */
  if (c_info->reported_already) {
    clean = 0;
  } else if (path_in_way(&opt->priv->paths, new_path, 1 << side_index, p)) {
    c_info->reported_already = 1;
    strbuf_add_separated_string_list(&collision_paths, ", ",
             &c_info->source_files);
    path_msg(opt, CONFLICT_DIR_RENAME_FILE_IN_WAY, 0,
       new_path, NULL, NULL, &c_info->source_files,
       _("CONFLICT (implicit dir rename): Existing "
         "file/dir at %s in the way of implicit "
         "directory rename(s) putting the following "
         "path(s) there: %s."),
       new_path, collision_paths.buf);
    clean = 0;
  } else if (c_info->source_files.nr > 1) {
    c_info->reported_already = 1;
    strbuf_add_separated_string_list(&collision_paths, ", ",
             &c_info->source_files);
    path_msg(opt, CONFLICT_DIR_RENAME_COLLISION, 0,
       new_path, NULL, NULL, &c_info->source_files,
       _("CONFLICT (implicit dir rename): Cannot map "
         "more than one path to %s; implicit directory "
         "renames tried to put these paths there: %s"),
       new_path, collision_paths.buf);
    clean = 0;
  }

  /* Free memory we no longer need */
  strbuf_release(&collision_paths);
  if (!clean && new_path) {
    free(new_path);
    return NULL;
  }

  return new_path;
}

static void get_provisional_directory_renames(struct merge_options *opt,
                unsigned side,
                int *clean)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;
  struct rename_info *renames = &opt->priv->renames;

  /*
   * Collapse
   *    dir_rename_count: old_directory -> {new_directory -> count}
   * down to
   *    dir_renames: old_directory -> best_new_directory
   * where best_new_directory is the one with the unique highest count.
   */
  strmap_for_each_entry(&renames->dir_rename_count[side], &iter, entry) {
    const char *source_dir = entry->key;
    struct strintmap *counts = entry->value;
    struct hashmap_iter count_iter;
    struct strmap_entry *count_entry;
    int max = 0;
    int bad_max = 0;
    const char *best = NULL;

    strintmap_for_each_entry(counts, &count_iter, count_entry) {
      const char *target_dir = count_entry->key;
      intptr_t count = (intptr_t)count_entry->value;

      if (count == max)
        bad_max = max;
      else if (count > max) {
        max = count;
        best = target_dir;
      }
    }

    if (max == 0)
      continue;

    if (bad_max == max) {
      path_msg(opt, CONFLICT_DIR_RENAME_SPLIT, 0,
         source_dir, NULL, NULL, NULL,
         _("CONFLICT (directory rename split): "
           "Unclear where to rename %s to; it was "
           "renamed to multiple other directories, "
           "with no destination getting a majority of "
           "the files."),
         source_dir);
      *clean = 0;
    } else {
      strmap_put(&renames->dir_renames[side],
           source_dir, (void*)best);
    }
  }
}

static void handle_directory_level_conflicts(struct merge_options *opt)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;
  struct string_list duplicated = STRING_LIST_INIT_NODUP;
  struct rename_info *renames = &opt->priv->renames;
  struct strmap *side1_dir_renames = &renames->dir_renames[MERGE_SIDE1];
  struct strmap *side2_dir_renames = &renames->dir_renames[MERGE_SIDE2];
  int i;

  strmap_for_each_entry(side1_dir_renames, &iter, entry) {
    if (strmap_contains(side2_dir_renames, entry->key))
      string_list_append(&duplicated, entry->key);
  }

  for (i = 0; i < duplicated.nr; i++) {
    strmap_remove(side1_dir_renames, duplicated.items[i].string, 0);
    strmap_remove(side2_dir_renames, duplicated.items[i].string, 0);
  }
  string_list_clear(&duplicated, 0);
}

static struct strmap_entry *check_dir_renamed(const char *path,
                struct strmap *dir_renames)
{
  char *temp = xstrdup(path);
  char *end;
  struct strmap_entry *e = NULL;

  while ((end = strrchr(temp, '/'))) {
    *end = '\0';
    e = strmap_get_entry(dir_renames, temp);
    if (e)
      break;
  }
  free(temp);
  return e;
}

static void compute_collisions(struct strmap *collisions,
             struct strmap *dir_renames,
             struct diff_queue_struct *pairs)
{
  int i;

  strmap_init_with_options(collisions, NULL, 0);
  if (strmap_empty(dir_renames))
    return;

  /*
   * Multiple files can be mapped to the same path due to directory
   * renames done by the other side of history.  Since that other
   * side of history could have merged multiple directories into one,
   * if our side of history added the same file basename to each of
   * those directories, then all N of them would get implicitly
   * renamed by the directory rename detection into the same path,
   * and we'd get an add/add/.../add conflict, and all those adds
   * from *this* side of history.  This is not representable in the
   * index, and users aren't going to easily be able to make sense of
   * it.  So we need to provide a good warning about what's
   * happening, and fall back to no-directory-rename detection
   * behavior for those paths.
   *
   * See testcases 9e and all of section 5 from t6423 for examples.
   */
  for (i = 0; i < pairs->nr; ++i) {
    struct strmap_entry *rename_info;
    struct collision_info *collision_info;
    char *new_path;
    struct diff_filepair *pair = pairs->queue[i];

    if (pair->status != 'A' && pair->status != 'R')
      continue;
    rename_info = check_dir_renamed(pair->two->path, dir_renames);
    if (!rename_info)
      continue;

    new_path = apply_dir_rename(rename_info, pair->two->path);
    assert(new_path);
    collision_info = strmap_get(collisions, new_path);
    if (collision_info) {
      free(new_path);
    } else {
      CALLOC_ARRAY(collision_info, 1);
      string_list_init_nodup(&collision_info->source_files);
      strmap_put(collisions, new_path, collision_info);
    }
    string_list_insert(&collision_info->source_files,
           pair->two->path);
  }
}

static void free_collisions(struct strmap *collisions)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;

  /* Free each value in the collisions map */
  strmap_for_each_entry(collisions, &iter, entry) {
    struct collision_info *info = entry->value;
    string_list_clear(&info->source_files, 0);
  }
  /*
   * In compute_collisions(), we set collisions.strdup_strings to 0
   * so that we wouldn't have to make another copy of the new_path
   * allocated by apply_dir_rename().  But now that we've used them
   * and have no other references to these strings, it is time to
   * deallocate them.
   */
  free_strmap_strings(collisions);
  strmap_clear(collisions, 1);
}

static char *check_for_directory_rename(struct merge_options *opt,
          const char *path,
          unsigned side_index,
          struct diff_filepair *p,
          struct strmap *dir_renames,
          struct strmap *dir_rename_exclusions,
          struct strmap *collisions,
          int *clean_merge)
{
  char *new_path;
  struct strmap_entry *rename_info;
  const char *new_dir;
  int other_side = 3 - side_index;

  /*
   * Cases where we don't have or don't want a directory rename for
   * this path.
   */
  if (strmap_empty(dir_renames))
    return NULL;
  if (strmap_get(&collisions[other_side], path))
    return NULL;
  rename_info = check_dir_renamed(path, dir_renames);
  if (!rename_info)
    return NULL;

  /*
   * This next part is a little weird.  We do not want to do an
   * implicit rename into a directory we renamed on our side, because
   * that will result in a spurious rename/rename(1to2) conflict.  An
   * example:
   *   Base commit: dumbdir/afile, otherdir/bfile
   *   Side 1:      smrtdir/afile, otherdir/bfile
   *   Side 2:      dumbdir/afile, dumbdir/bfile
   * Here, while working on Side 1, we could notice that otherdir was
   * renamed/merged to dumbdir, and change the diff_filepair for
   * otherdir/bfile into a rename into dumbdir/bfile.  However, Side
   * 2 will notice the rename from dumbdir to smrtdir, and do the
   * transitive rename to move it from dumbdir/bfile to
   * smrtdir/bfile.  That gives us bfile in dumbdir vs being in
   * smrtdir, a rename/rename(1to2) conflict.  We really just want
   * the file to end up in smrtdir.  And the way to achieve that is
   * to not let Side1 do the rename to dumbdir, since we know that is
   * the source of one of our directory renames.
   *
   * That's why dir_rename_exclusions is here.
   *
   * As it turns out, this also prevents N-way transient rename
   * confusion; See testcases 9c and 9d of t6423.
   */
  new_dir = rename_info->value; /* old_dir = rename_info->key; */
  if (strmap_contains(dir_rename_exclusions, new_dir)) {
    path_msg(opt, INFO_DIR_RENAME_SKIPPED_DUE_TO_RERENAME, 1,
       rename_info->key, path, new_dir, NULL,
       _("WARNING: Avoiding applying %s -> %s rename "
         "to %s, because %s itself was renamed."),
       rename_info->key, new_dir, path, new_dir);
    return NULL;
  }

  new_path = handle_path_level_conflicts(opt, path, side_index, p,
                 rename_info,
                 &collisions[side_index]);
  *clean_merge &= (new_path != NULL);

  return new_path;
}

static void apply_directory_rename_modifications(struct merge_options *opt,
             struct diff_filepair *pair,
             char *new_path)
{
  /*
   * The basic idea is to get the conflict_info from opt->priv->paths
   * at old path, and insert it into new_path; basically just this:
   *     ci = strmap_get(&opt->priv->paths, old_path);
   *     strmap_remove(&opt->priv->paths, old_path, 0);
   *     strmap_put(&opt->priv->paths, new_path, ci);
   * However, there are some factors complicating this:
   *     - opt->priv->paths may already have an entry at new_path
   *     - Each ci tracks its containing directory, so we need to
   *       update that
   *     - If another ci has the same containing directory, then
   *       the two char*'s MUST point to the same location.  See the
   *       comment in struct merged_info.  strcmp equality is not
   *       enough; we need pointer equality.
   *     - opt->priv->paths must hold the parent directories of any
   *       entries that are added.  So, if this directory rename
   *       causes entirely new directories, we must recursively add
   *       parent directories.
   *     - For each parent directory added to opt->priv->paths, we
   *       also need to get its parent directory stored in its
   *       conflict_info->merged.directory_name with all the same
   *       requirements about pointer equality.
   */
  struct string_list dirs_to_insert = STRING_LIST_INIT_NODUP;
  struct conflict_info *ci, *new_ci;
  struct strmap_entry *entry;
  const char *branch_with_new_path, *branch_with_dir_rename;
  const char *old_path = pair->two->path;
  const char *parent_name;
  const char *cur_path;
  int i, len;

  entry = strmap_get_entry(&opt->priv->paths, old_path);
  old_path = entry->key;
  ci = entry->value;
  VERIFY_CI(ci);

  /* Find parent directories missing from opt->priv->paths */
  cur_path = mem_pool_strdup(&opt->priv->pool, new_path);
  free((char*)new_path);
  new_path = (char *)cur_path;

  while (1) {
    /* Find the parent directory of cur_path */
    const char *last_slash = strrchr(cur_path, '/');
    if (last_slash) {
      parent_name = mem_pool_strndup(&opt->priv->pool,
                   cur_path,
                   last_slash - cur_path);
    } else {
      parent_name = opt->priv->toplevel_dir;
      break;
    }

    /* Look it up in opt->priv->paths */
    entry = strmap_get_entry(&opt->priv->paths, parent_name);
    if (entry) {
      parent_name = entry->key; /* reuse known pointer */
      break;
    }

    /* Record this is one of the directories we need to insert */
    string_list_append(&dirs_to_insert, parent_name);
    cur_path = parent_name;
  }

  /* Traverse dirs_to_insert and insert them into opt->priv->paths */
  for (i = dirs_to_insert.nr-1; i >= 0; --i) {
    struct conflict_info *dir_ci;
    char *cur_dir = dirs_to_insert.items[i].string;

    dir_ci = mem_pool_calloc(&opt->priv->pool, 1, sizeof(*dir_ci));

    dir_ci->merged.directory_name = parent_name;
    len = strlen(parent_name);
    /* len+1 because of trailing '/' character */
    dir_ci->merged.basename_offset = (len > 0 ? len+1 : len);
    dir_ci->dirmask = ci->filemask;
    strmap_put(&opt->priv->paths, cur_dir, dir_ci);

    parent_name = cur_dir;
  }

  assert(ci->filemask == 2 || ci->filemask == 4);
  assert(ci->dirmask == 0 || ci->dirmask == 1);
  if (ci->dirmask == 0)
    strmap_remove(&opt->priv->paths, old_path, 0);
  else {
    /*
     * This file exists on one side, but we still had a directory
     * at the old location that we can't remove until after
     * processing all paths below it.  So, make a copy of ci in
     * new_ci and only put the file information into it.
     */
    new_ci = mem_pool_calloc(&opt->priv->pool, 1, sizeof(*new_ci));
    memcpy(new_ci, ci, sizeof(*ci));
    assert(!new_ci->match_mask);
    new_ci->dirmask = 0;
    new_ci->stages[1].mode = 0;
    oidcpy(&new_ci->stages[1].oid, null_oid(opt->repo->hash_algo));

    /*
     * Now that we have the file information in new_ci, make sure
     * ci only has the directory information.
     */
    ci->filemask = 0;
    ci->merged.clean = 1;
    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
      if (ci->dirmask & (1 << i))
        continue;
      /* zero out any entries related to files */
      ci->stages[i].mode = 0;
      oidcpy(&ci->stages[i].oid, null_oid(opt->repo->hash_algo));
    }

    /* Now we want to focus on new_ci, so reassign ci to it. */
    ci = new_ci;
  }

  branch_with_new_path   = (ci->filemask == 2) ? opt->branch1 : opt->branch2;
  branch_with_dir_rename = (ci->filemask == 2) ? opt->branch2 : opt->branch1;

  /* Now, finally update ci and stick it into opt->priv->paths */
  ci->merged.directory_name = parent_name;
  len = strlen(parent_name);
  ci->merged.basename_offset = (len > 0 ? len+1 : len);
  new_ci = strmap_get(&opt->priv->paths, new_path);
  if (!new_ci) {
    /* Place ci back into opt->priv->paths, but at new_path */
    strmap_put(&opt->priv->paths, new_path, ci);
  } else {
    int index;

    /* A few sanity checks */
    VERIFY_CI(new_ci);
    assert(ci->filemask == 2 || ci->filemask == 4);
    assert((new_ci->filemask & ci->filemask) == 0);
    assert(!new_ci->merged.clean);

    /* Copy stuff from ci into new_ci */
    new_ci->filemask |= ci->filemask;
    if (new_ci->dirmask)
      new_ci->df_conflict = 1;
    index = (ci->filemask >> 1);
    new_ci->pathnames[index] = ci->pathnames[index];
    new_ci->stages[index].mode = ci->stages[index].mode;
    oidcpy(&new_ci->stages[index].oid, &ci->stages[index].oid);

    ci = new_ci;
  }

  if (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE) {
    /* Notify user of updated path */
    if (pair->status == 'A')
      path_msg(opt, INFO_DIR_RENAME_APPLIED, 1,
         new_path, old_path, NULL, NULL,
         _("Path updated: %s added in %s inside a "
           "directory that was renamed in %s; moving "
           "it to %s."),
         old_path, branch_with_new_path,
         branch_with_dir_rename, new_path);
    else
      path_msg(opt, INFO_DIR_RENAME_APPLIED, 1,
         new_path, old_path, NULL, NULL,
         _("Path updated: %s renamed to %s in %s, "
           "inside a directory that was renamed in %s; "
           "moving it to %s."),
         pair->one->path, old_path, branch_with_new_path,
         branch_with_dir_rename, new_path);
  } else {
    /*
     * opt->detect_directory_renames has the value
     * MERGE_DIRECTORY_RENAMES_CONFLICT, so mark these as conflicts.
     */
    ci->path_conflict = 1;
    if (pair->status == 'A')
      path_msg(opt, CONFLICT_DIR_RENAME_SUGGESTED, 1,
         new_path, old_path, NULL, NULL,
         _("CONFLICT (file location): %s added in %s "
           "inside a directory that was renamed in %s, "
           "suggesting it should perhaps be moved to "
           "%s."),
         old_path, branch_with_new_path,
         branch_with_dir_rename, new_path);
    else
      path_msg(opt, CONFLICT_DIR_RENAME_SUGGESTED, 1,
         new_path, old_path, NULL, NULL,
         _("CONFLICT (file location): %s renamed to %s "
           "in %s, inside a directory that was renamed "
           "in %s, suggesting it should perhaps be "
           "moved to %s."),
         pair->one->path, old_path, branch_with_new_path,
         branch_with_dir_rename, new_path);
  }

  /*
   * Finally, record the new location.
   */
  pair->two->path = new_path;

  string_list_clear(&dirs_to_insert, 0);
}

/*** Function Grouping: functions related to regular rename detection ***/

static int process_renames(struct merge_options *opt,
         struct diff_queue_struct *renames)
{
  int clean_merge = 1, i;

  for (i = 0; i < renames->nr; ++i) {
    const char *oldpath = NULL, *newpath;
    struct diff_filepair *pair = renames->queue[i];
    struct conflict_info *oldinfo = NULL, *newinfo = NULL;
    struct strmap_entry *old_ent, *new_ent;
    unsigned int old_sidemask;
    int target_index, other_source_index;
    int source_deleted, collision, type_changed;
    const char *rename_branch = NULL, *delete_branch = NULL;

    old_ent = strmap_get_entry(&opt->priv->paths, pair->one->path);
    new_ent = strmap_get_entry(&opt->priv->paths, pair->two->path);
    if (old_ent) {
      oldpath = old_ent->key;
      oldinfo = old_ent->value;
    }
    newpath = pair->two->path;
    if (new_ent) {
      newpath = new_ent->key;
      newinfo = new_ent->value;
    }

    /*
     * Directory renames can result in rename-to-self; the code
     * below assumes we have A->B with different A & B, and tries
     * to move all entries to path B.  If A & B are the same path,
     * the logic can get confused, so skip further processing when
     * A & B are already the same path.
     *
     * As a reminder, we can avoid strcmp here because all paths
     * are interned in opt->priv->paths; see the comment above
     * "paths" in struct merge_options_internal.
     */
    if (oldpath == newpath)
      continue;

    /*
     * If pair->one->path isn't in opt->priv->paths, that means
     * that either directory rename detection removed that
     * path, or a parent directory of oldpath was resolved and
     * we don't even need the rename; in either case, we can
     * skip it.  If oldinfo->merged.clean, then the other side
     * of history had no changes to oldpath and we don't need
     * the rename and can skip it.
     */
    if (!oldinfo || oldinfo->merged.clean)
      continue;

    /*
     * Rename caching from a previous commit might give us an
     * irrelevant rename for the current commit.
     *
     * Imagine:
     *     foo/A -> bar/A
     * was a cached rename for the upstream side from the
     * previous commit (without the directories being renamed),
     * but the next commit being replayed
     *     * does NOT add or delete files
     *     * does NOT have directory renames
     *     * does NOT modify any files under bar/
     *     * does NOT modify foo/A
     *     * DOES modify other files under foo/ (otherwise the
     *       !oldinfo check above would have already exited for
     *       us)
     * In such a case, our trivial directory resolution will
     * have already merged bar/, and our attempt to process
     * the cached
     *     foo/A -> bar/A
     * would be counterproductive, and lack the necessary
     * information anyway.  Skip such renames.
     */
    if (!newinfo)
      continue;

    /*
     * diff_filepairs have copies of pathnames, thus we have to
     * use standard 'strcmp()' (negated) instead of '=='.
     */
    if (i + 1 < renames->nr &&
        !strcmp(oldpath, renames->queue[i+1]->one->path)) {
      /* Handle rename/rename(1to2) or rename/rename(1to1) */
      const char *pathnames[3];
      struct version_info merged;
      struct conflict_info *base, *side1, *side2;
      unsigned was_binary_blob = 0;
      const int record_object = true;

      pathnames[0] = oldpath;
      pathnames[1] = newpath;
      pathnames[2] = renames->queue[i+1]->two->path;

      base = strmap_get(&opt->priv->paths, pathnames[0]);
      side1 = strmap_get(&opt->priv->paths, pathnames[1]);
      side2 = strmap_get(&opt->priv->paths, pathnames[2]);

      VERIFY_CI(base);
      VERIFY_CI(side1);
      VERIFY_CI(side2);

      if (!strcmp(pathnames[1], pathnames[2])) {
        struct rename_info *ri = &opt->priv->renames;
        int j;

        /* Both sides renamed the same way */
        assert(side1 == side2);
        memcpy(&side1->stages[0], &base->stages[0],
               sizeof(merged));
        side1->filemask |= (1 << MERGE_BASE);
        /* Mark base as resolved by removal */
        base->merged.is_null = 1;
        base->merged.clean = 1;

        /*
         * Disable remembering renames optimization;
         * rename/rename(1to1) is incredibly rare, and
         * just disabling the optimization is easier
         * than purging cached_pairs,
         * cached_target_names, and dir_rename_counts.
         */
        for (j = 0; j < 3; j++)
          ri->merge_trees[j] = NULL;

        /* We handled both renames, i.e. i+1 handled */
        i++;
        /* Move to next rename */
        continue;
      }

      /* This is a rename/rename(1to2) */
      clean_merge = handle_content_merge(opt,
                 pair->one->path,
                 &base->stages[0],
                 &side1->stages[1],
                 &side2->stages[2],
                 pathnames,
                 1 + 2 * opt->priv->call_depth,
                 record_object,
                 &merged);
      if (clean_merge < 0)
        return -1;
      if (!clean_merge &&
          merged.mode == side1->stages[1].mode &&
          oideq(&merged.oid, &side1->stages[1].oid))
        was_binary_blob = 1;
      memcpy(&side1->stages[1], &merged, sizeof(merged));
      if (was_binary_blob) {
        /*
         * Getting here means we were attempting to
         * merge a binary blob.
         *
         * Since we can't merge binaries,
         * handle_content_merge() just takes one
         * side.  But we don't want to copy the
         * contents of one side to both paths.  We
         * used the contents of side1 above for
         * side1->stages, let's use the contents of
         * side2 for side2->stages below.
         */
        oidcpy(&merged.oid, &side2->stages[2].oid);
        merged.mode = side2->stages[2].mode;
      }
      memcpy(&side2->stages[2], &merged, sizeof(merged));

      side1->path_conflict = 1;
      side2->path_conflict = 1;
      /*
       * TODO: For renames we normally remove the path at the
       * old name.  It would thus seem consistent to do the
       * same for rename/rename(1to2) cases, but we haven't
       * done so traditionally and a number of the regression
       * tests now encode an expectation that the file is
       * left there at stage 1.  If we ever decide to change
       * this, add the following two lines here:
       *    base->merged.is_null = 1;
       *    base->merged.clean = 1;
       * and remove the setting of base->path_conflict to 1.
       */
      base->path_conflict = 1;
      path_msg(opt, CONFLICT_RENAME_RENAME, 0,
         pathnames[0], pathnames[1], pathnames[2], NULL,
         _("CONFLICT (rename/rename): %s renamed to "
           "%s in %s and to %s in %s."),
         pathnames[0],
         pathnames[1], opt->branch1,
         pathnames[2], opt->branch2);

      i++; /* We handled both renames, i.e. i+1 handled */
      continue;
    }

    VERIFY_CI(oldinfo);
    VERIFY_CI(newinfo);
    target_index = pair->score; /* from collect_renames() */
    assert(target_index == 1 || target_index == 2);
    other_source_index = 3 - target_index;
    old_sidemask = (1 << other_source_index); /* 2 or 4 */
    source_deleted = (oldinfo->filemask == 1);
    collision = ((newinfo->filemask & old_sidemask) != 0);
    type_changed = !source_deleted &&
      (S_ISREG(oldinfo->stages[other_source_index].mode) !=
       S_ISREG(newinfo->stages[target_index].mode));
    if (type_changed && collision) {
      /*
       * special handling so later blocks can handle this...
       *
       * if type_changed && collision are both true, then this
       * was really a double rename, but one side wasn't
       * detected due to lack of break detection.  I.e.
       * something like
       *    orig: has normal file 'foo'
       *    side1: renames 'foo' to 'bar', adds 'foo' symlink
       *    side2: renames 'foo' to 'bar'
       * In this case, the foo->bar rename on side1 won't be
       * detected because the new symlink named 'foo' is
       * there and we don't do break detection.  But we detect
       * this here because we don't want to merge the content
       * of the foo symlink with the foo->bar file, so we
       * have some logic to handle this special case.  The
       * easiest way to do that is make 'bar' on side1 not
       * be considered a colliding file but the other part
       * of a normal rename.  If the file is very different,
       * well we're going to get content merge conflicts
       * anyway so it doesn't hurt.  And if the colliding
       * file also has a different type, that'll be handled
       * by the content merge logic in process_entry() too.
       *
       * See also t6430, 'rename vs. rename/symlink'
       */
      collision = 0;
    }
    if (source_deleted) {
      if (target_index == 1) {
        rename_branch = opt->branch1;
        delete_branch = opt->branch2;
      } else {
        rename_branch = opt->branch2;
        delete_branch = opt->branch1;
      }
    }

    assert(source_deleted || oldinfo->filemask & old_sidemask ||
           !strcmp(pair->one->path, pair->two->path));

    /* Need to check for special types of rename conflicts... */
    if (collision && !source_deleted) {
      /* collision: rename/add or rename/rename(2to1) */
      const char *pathnames[3];
      struct version_info merged;

      struct conflict_info *base, *side1, *side2;
      int clean;
      const int record_object = true;

      pathnames[0] = oldpath;
      pathnames[other_source_index] = oldpath;
      pathnames[target_index] = newpath;

      base = strmap_get(&opt->priv->paths, pathnames[0]);
      side1 = strmap_get(&opt->priv->paths, pathnames[1]);
      side2 = strmap_get(&opt->priv->paths, pathnames[2]);

      VERIFY_CI(base);
      VERIFY_CI(side1);
      VERIFY_CI(side2);

      clean = handle_content_merge(opt, pair->one->path,
                 &base->stages[0],
                 &side1->stages[1],
                 &side2->stages[2],
                 pathnames,
                 1 + 2 * opt->priv->call_depth,
                 record_object,
                 &merged);
      if (clean < 0)
        return -1;

      memcpy(&newinfo->stages[target_index], &merged,
             sizeof(merged));
      if (!clean) {
        path_msg(opt, CONFLICT_RENAME_COLLIDES, 0,
           newpath, oldpath, NULL, NULL,
           _("CONFLICT (rename involved in "
             "collision): rename of %s -> %s has "
             "content conflicts AND collides "
             "with another path; this may result "
             "in nested conflict markers."),
           oldpath, newpath);
      }
    } else if (collision && source_deleted) {
      /*
       * rename/add/delete or rename/rename(2to1)/delete:
       * since oldpath was deleted on the side that didn't
       * do the rename, there's not much of a content merge
       * we can do for the rename.  oldinfo->merged.is_null
       * was already set, so we just leave things as-is so
       * they look like an add/add conflict.
       */

      newinfo->path_conflict = 1;
      path_msg(opt, CONFLICT_RENAME_DELETE, 0,
         newpath, oldpath, NULL, NULL,
         _("CONFLICT (rename/delete): %s renamed "
           "to %s in %s, but deleted in %s."),
         oldpath, newpath, rename_branch, delete_branch);
    } else {
      /*
       * a few different cases...start by copying the
       * existing stage(s) from oldinfo over the newinfo
       * and update the pathname(s).
       */
      memcpy(&newinfo->stages[0], &oldinfo->stages[0],
             sizeof(newinfo->stages[0]));
      newinfo->filemask |= (1 << MERGE_BASE);
      newinfo->pathnames[0] = oldpath;
      if (type_changed) {
        /* rename vs. typechange */
        /* Mark the original as resolved by removal */
        memcpy(&oldinfo->stages[0].oid, null_oid(opt->repo->hash_algo),
               sizeof(oldinfo->stages[0].oid));
        oldinfo->stages[0].mode = 0;
        oldinfo->filemask &= 0x06;
      } else if (source_deleted) {
        /* rename/delete */
        newinfo->path_conflict = 1;
        path_msg(opt, CONFLICT_RENAME_DELETE, 0,
           newpath, oldpath, NULL, NULL,
           _("CONFLICT (rename/delete): %s renamed"
             " to %s in %s, but deleted in %s."),
           oldpath, newpath,
           rename_branch, delete_branch);
      } else {
        /* normal rename */
        memcpy(&newinfo->stages[other_source_index],
               &oldinfo->stages[other_source_index],
               sizeof(newinfo->stages[0]));
        newinfo->filemask |= (1 << other_source_index);
        newinfo->pathnames[other_source_index] = oldpath;
      }
    }

    if (!type_changed) {
      /* Mark the original as resolved by removal */
      oldinfo->merged.is_null = 1;
      oldinfo->merged.clean = 1;
    }

  }

  return clean_merge;
}

static inline int possible_side_renames(struct rename_info *renames,
          unsigned side_index)
{
  return renames->pairs[side_index].nr > 0 &&
         !strintmap_empty(&renames->relevant_sources[side_index]);
}

static inline int possible_renames(struct rename_info *renames)
{
  return possible_side_renames(renames, 1) ||
         possible_side_renames(renames, 2) ||
         !strmap_empty(&renames->cached_pairs[1]) ||
         !strmap_empty(&renames->cached_pairs[2]);
}

static void resolve_diffpair_statuses(struct diff_queue_struct *q)
{
  /*
   * A simplified version of diff_resolve_rename_copy(); would probably
   * just use that function but it's static...
   */
  int i;
  struct diff_filepair *p;

  for (i = 0; i < q->nr; ++i) {
    p = q->queue[i];
    p->status = 0; /* undecided */
    if (!DIFF_FILE_VALID(p->one))
      p->status = DIFF_STATUS_ADDED;
    else if (!DIFF_FILE_VALID(p->two))
      p->status = DIFF_STATUS_DELETED;
    else if (DIFF_PAIR_RENAME(p))
      p->status = DIFF_STATUS_RENAMED;
  }
}

static void prune_cached_from_relevant(struct rename_info *renames,
               unsigned side)
{
  /* Reason for this function described in add_pair() */
  struct hashmap_iter iter;
  struct strmap_entry *entry;

  /* Remove from relevant_sources all entries in cached_pairs[side] */
  strmap_for_each_entry(&renames->cached_pairs[side], &iter, entry) {
    strintmap_remove(&renames->relevant_sources[side],
         entry->key);
  }
  /* Remove from relevant_sources all entries in cached_irrelevant[side] */
  strset_for_each_entry(&renames->cached_irrelevant[side], &iter, entry) {
    strintmap_remove(&renames->relevant_sources[side],
         entry->key);
  }
}

static void use_cached_pairs(struct merge_options *opt,
           struct strmap *cached_pairs,
           struct diff_queue_struct *pairs)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;

  /*
   * Add to side_pairs all entries from renames->cached_pairs[side_index].
   * (Info in cached_irrelevant[side_index] is not relevant here.)
   */
  strmap_for_each_entry(cached_pairs, &iter, entry) {
    struct diff_filespec *one, *two;
    const char *old_name = entry->key;
    const char *new_name = entry->value;
    if (!new_name)
      new_name = old_name;

    /*
     * cached_pairs has *copies* of old_name and new_name,
     * because it has to persist across merges.  Since
     * pool_alloc_filespec() will just re-use the existing
     * filenames, which will also get re-used by
     * opt->priv->paths if they become renames, and then
     * get freed at the end of the merge, that would leave
     * the copy in cached_pairs dangling.  Avoid this by
     * making a copy here.
     */
    old_name = mem_pool_strdup(&opt->priv->pool, old_name);
    new_name = mem_pool_strdup(&opt->priv->pool, new_name);

    /* We don't care about oid/mode, only filenames and status */
    one = pool_alloc_filespec(&opt->priv->pool, old_name);
    two = pool_alloc_filespec(&opt->priv->pool, new_name);
    pool_diff_queue(&opt->priv->pool, pairs, one, two);
    pairs->queue[pairs->nr-1]->status = entry->value ? 'R' : 'D';
  }
}

static void cache_new_pair(struct rename_info *renames,
         int side,
         char *old_path,
         char *new_path,
         int free_old_value)
{
  char *old_value;
  new_path = xstrdup(new_path);
  old_value = strmap_put(&renames->cached_pairs[side],
             old_path, new_path);
  strset_add(&renames->cached_target_names[side], new_path);
  if (free_old_value)
    free(old_value);
  else
    assert(!old_value);
}

static void possibly_cache_new_pair(struct rename_info *renames,
            struct diff_filepair *p,
            unsigned side,
            char *new_path)
{
  int dir_renamed_side = 0;

  if (new_path) {
    /*
     * Directory renames happen on the other side of history from
     * the side that adds new files to the old directory.
     */
    dir_renamed_side = 3 - side;
  } else {
    int val = strintmap_get(&renames->relevant_sources[side],
          p->one->path);
    if (val == RELEVANT_NO_MORE) {
      assert(p->status == 'D');
      strset_add(&renames->cached_irrelevant[side],
           p->one->path);
    }
    if (val <= 0)
      return;
  }

  if (p->status == 'D') {
    /*
     * If we already had this delete, we'll just set it's value
     * to NULL again, so no harm.
     */
    strmap_put(&renames->cached_pairs[side], p->one->path, NULL);
  } else if (p->status == 'R') {
    if (!new_path)
      new_path = p->two->path;
    else
      cache_new_pair(renames, dir_renamed_side,
               p->two->path, new_path, 0);
    cache_new_pair(renames, side, p->one->path, new_path, 1);
  } else if (p->status == 'A' && new_path) {
    cache_new_pair(renames, dir_renamed_side,
             p->two->path, new_path, 0);
  }
}

static int compare_pairs(const void *a_, const void *b_)
{
  const struct diff_filepair *a = *((const struct diff_filepair **)a_);
  const struct diff_filepair *b = *((const struct diff_filepair **)b_);

  return strcmp(a->one->path, b->one->path);
}

/* Call diffcore_rename() to update deleted/added pairs into rename pairs */
static int detect_regular_renames(struct merge_options *opt,
          unsigned side_index)
{
  struct diff_options diff_opts;
  struct rename_info *renames = &opt->priv->renames;

  prune_cached_from_relevant(renames, side_index);
  if (!possible_side_renames(renames, side_index)) {
    /*
     * No rename detection needed for this side, but we still need
     * to make sure 'adds' are marked correctly in case the other
     * side had directory renames.
     */
    resolve_diffpair_statuses(&renames->pairs[side_index]);
    return 0;
  }

  partial_clear_dir_rename_count(&renames->dir_rename_count[side_index]);
  repo_diff_setup(opt->repo, &diff_opts);
  diff_opts.flags.recursive = 1;
  diff_opts.flags.rename_empty = 0;
  diff_opts.detect_rename = DIFF_DETECT_RENAME;
  diff_opts.rename_limit = opt->rename_limit;
  if (opt->rename_limit <= 0)
    diff_opts.rename_limit = 7000;
  diff_opts.rename_score = opt->rename_score;
  diff_opts.show_rename_progress = opt->show_rename_progress;
  diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
  diff_setup_done(&diff_opts);

  diff_queued_diff = renames->pairs[side_index];
  trace2_region_enter("diff", "diffcore_rename", opt->repo);
  diffcore_rename_extended(&diff_opts,
         &opt->priv->pool,
         &renames->relevant_sources[side_index],
         &renames->dirs_removed[side_index],
         &renames->dir_rename_count[side_index],
         &renames->cached_pairs[side_index]);
  trace2_region_leave("diff", "diffcore_rename", opt->repo);
  resolve_diffpair_statuses(&diff_queued_diff);

  if (diff_opts.needed_rename_limit > 0)
    renames->redo_after_renames = 0;
  if (diff_opts.needed_rename_limit > renames->needed_limit)
    renames->needed_limit = diff_opts.needed_rename_limit;

  renames->pairs[side_index] = diff_queued_diff;

  diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
  diff_queued_diff.nr = 0;
  diff_queued_diff.queue = NULL;
  diff_flush(&diff_opts);

  return 1;
}

/*
 * Get information of all renames which occurred in 'side_pairs', making use
 * of any implicit directory renames in side_dir_renames (also making use of
 * implicit directory renames rename_exclusions as needed by
 * check_for_directory_rename()).  Add all (updated) renames into result.
 */
static int collect_renames(struct merge_options *opt,
         struct diff_queue_struct *result,
         unsigned side_index,
         struct strmap *collisions,
         struct strmap *dir_renames_for_side,
         struct strmap *rename_exclusions)
{
  int i, clean = 1;
  struct diff_queue_struct *side_pairs;
  struct rename_info *renames = &opt->priv->renames;

  side_pairs = &renames->pairs[side_index];

  for (i = 0; i < side_pairs->nr; ++i) {
    struct diff_filepair *p = side_pairs->queue[i];
    char *new_path; /* non-NULL only with directory renames */

    if (p->status != 'A' && p->status != 'R') {
      possibly_cache_new_pair(renames, p, side_index, NULL);
      pool_diff_free_filepair(&opt->priv->pool, p);
      continue;
    }
    if (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_NONE &&
        p->status == 'R') {
      possibly_cache_new_pair(renames, p, side_index, NULL);
      goto skip_directory_renames;
    }

    new_path = check_for_directory_rename(opt, p->two->path,
                  side_index, p,
                  dir_renames_for_side,
                  rename_exclusions,
                  collisions,
                  &clean);

    possibly_cache_new_pair(renames, p, side_index, new_path);
    if (p->status != 'R' && !new_path) {
      pool_diff_free_filepair(&opt->priv->pool, p);
      continue;
    }

    if (new_path)
      apply_directory_rename_modifications(opt, p, new_path);

skip_directory_renames:
    /*
     * p->score comes back from diffcore_rename_extended() with
     * the similarity of the renamed file.  The similarity was
     * used to determine that the two files were related and
     * are a rename, which we have already used, but beyond
     * that we have no use for the similarity.  So p->score is
     * now irrelevant.  However, process_renames() will need to
     * know which side of the merge this rename was associated
     * with, so overwrite p->score with that value.
     */
    p->score = side_index;
    result->queue[result->nr++] = p;
  }

  return clean;
}

static int detect_and_process_renames(struct merge_options *opt)
{
  struct diff_queue_struct combined = { 0 };
  struct rename_info *renames = &opt->priv->renames;
  struct strmap collisions[3];
  int need_dir_renames, s, i, clean = 1;
  unsigned detection_run = 0;

  if (!possible_renames(renames))
    goto cleanup;
  if (!opt->detect_renames) {
    renames->redo_after_renames = 0;
    renames->cached_pairs_valid_side = 0;
    goto cleanup;
  }

  trace2_region_enter("merge", "regular renames", opt->repo);
  detection_run |= detect_regular_renames(opt, MERGE_SIDE1);
  detection_run |= detect_regular_renames(opt, MERGE_SIDE2);
  if (renames->needed_limit) {
    renames->cached_pairs_valid_side = 0;
    renames->redo_after_renames = 0;
  }
  if (renames->redo_after_renames && detection_run) {
    int i, side;
    struct diff_filepair *p;

    /* Cache the renames, we found */
    for (side = MERGE_SIDE1; side <= MERGE_SIDE2; side++) {
      for (i = 0; i < renames->pairs[side].nr; ++i) {
        p = renames->pairs[side].queue[i];
        possibly_cache_new_pair(renames, p, side, NULL);
      }
    }

    /* Restart the merge with the cached renames */
    renames->redo_after_renames = 2;
    trace2_region_leave("merge", "regular renames", opt->repo);
    goto cleanup;
  }
  use_cached_pairs(opt, &renames->cached_pairs[1], &renames->pairs[1]);
  use_cached_pairs(opt, &renames->cached_pairs[2], &renames->pairs[2]);
  trace2_region_leave("merge", "regular renames", opt->repo);

  trace2_region_enter("merge", "directory renames", opt->repo);
  need_dir_renames =
    !opt->priv->call_depth &&
    (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE ||
     opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT);

  if (need_dir_renames) {
    get_provisional_directory_renames(opt, MERGE_SIDE1, &clean);
    get_provisional_directory_renames(opt, MERGE_SIDE2, &clean);
    handle_directory_level_conflicts(opt);
  }

  ALLOC_GROW(combined.queue,
       renames->pairs[1].nr + renames->pairs[2].nr,
       combined.alloc);
  for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++) {
    int other_side = 3 - i;
    compute_collisions(&collisions[i],
           &renames->dir_renames[other_side],
           &renames->pairs[i]);
  }
  clean &= collect_renames(opt, &combined, MERGE_SIDE1,
         collisions,
         &renames->dir_renames[2],
         &renames->dir_renames[1]);
  clean &= collect_renames(opt, &combined, MERGE_SIDE2,
         collisions,
         &renames->dir_renames[1],
         &renames->dir_renames[2]);
  for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++)
    free_collisions(&collisions[i]);
  STABLE_QSORT(combined.queue, combined.nr, compare_pairs);
  trace2_region_leave("merge", "directory renames", opt->repo);

  trace2_region_enter("merge", "process renames", opt->repo);
  clean &= process_renames(opt, &combined);
  trace2_region_leave("merge", "process renames", opt->repo);

  goto simple_cleanup; /* collect_renames() handles some of cleanup */

cleanup:
  /*
   * Free now unneeded filepairs, which would have been handled
   * in collect_renames() normally but we skipped that code.
   */
  for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
    struct diff_queue_struct *side_pairs;
    int i;

    side_pairs = &renames->pairs[s];
    for (i = 0; i < side_pairs->nr; ++i) {
      struct diff_filepair *p = side_pairs->queue[i];
      pool_diff_free_filepair(&opt->priv->pool, p);
    }
  }

simple_cleanup:
  /* Free memory for renames->pairs[] and combined */
  for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
    free(renames->pairs[s].queue);
    diff_queue_init(&renames->pairs[s]);
  }
  for (i = 0; i < combined.nr; i++)
    pool_diff_free_filepair(&opt->priv->pool, combined.queue[i]);
  free(combined.queue);

  return clean;
}

/*** Function Grouping: functions related to process_entries() ***/

static int sort_dirs_next_to_their_children(const char *one, const char *two)
{
  unsigned char c1, c2;

  /*
   * Here we only care that entries for directories appear adjacent
   * to and before files underneath the directory.  We can achieve
   * that by pretending to add a trailing slash to every file and
   * then sorting.  In other words, we do not want the natural
   * sorting of
   *     foo
   *     foo.txt
   *     foo/bar
   * Instead, we want "foo" to sort as though it were "foo/", so that
   * we instead get
   *     foo.txt
   *     foo
   *     foo/bar
   * To achieve this, we basically implement our own strcmp, except that
   * if we get to the end of either string instead of comparing NUL to
   * another character, we compare '/' to it.
   *
   * If this unusual "sort as though '/' were appended" perplexes
   * you, perhaps it will help to note that this is not the final
   * sort.  write_tree() will sort again without the trailing slash
   * magic, but just on paths immediately under a given tree.
   *
   * The reason to not use df_name_compare directly was that it was
   * just too expensive (we don't have the string lengths handy), so
   * it was reimplemented.
   */

  /*
   * NOTE: This function will never be called with two equal strings,
   * because it is used to sort the keys of a strmap, and strmaps have
   * unique keys by construction.  That simplifies our c1==c2 handling
   * below.
   */

  while (*one && (*one == *two)) {
    one++;
    two++;
  }

  c1 = *one ? *one : '/';
  c2 = *two ? *two : '/';

  if (c1 == c2) {
    /* Getting here means one is a leading directory of the other */
    return (*one) ? 1 : -1;
  } else
    return c1 - c2;
}

static int read_oid_strbuf(struct merge_options *opt,
         const struct object_id *oid,
         struct strbuf *dst,
         const char *path)
{
  void *buf;
  enum object_type type;
  unsigned long size;
  buf = odb_read_object(opt->repo->objects, oid, &type, &size);
  if (!buf) {
    path_msg(opt, ERROR_OBJECT_READ_FAILED, 0,
       path, NULL, NULL, NULL,
       _("error: cannot read object %s"), oid_to_hex(oid));
    return -1;
  }
  if (type != OBJ_BLOB) {
    free(buf);
    path_msg(opt, ERROR_OBJECT_NOT_A_BLOB, 0,
       path, NULL, NULL, NULL,
       _("error: object %s is not a blob"), oid_to_hex(oid));
    return -1;
  }
  strbuf_attach(dst, buf, size, size + 1);
  return 0;
}

static int blob_unchanged(struct merge_options *opt,
        const struct version_info *base,
        const struct version_info *side,
        const char *path)
{
  struct strbuf basebuf = STRBUF_INIT;
  struct strbuf sidebuf = STRBUF_INIT;
  int ret = 0; /* assume changed for safety */
  struct index_state *idx = &opt->priv->attr_index;

  if (!idx->initialized)
    initialize_attr_index(opt);

  if (base->mode != side->mode)
    return 0;
  if (oideq(&base->oid, &side->oid))
    return 1;

  if (read_oid_strbuf(opt, &base->oid, &basebuf, path) ||
      read_oid_strbuf(opt, &side->oid, &sidebuf, path))
    goto error_return;
  /*
   * Note: binary | is used so that both renormalizations are
   * performed.  Comparison can be skipped if both files are
   * unchanged since their sha1s have already been compared.
   */
  if (renormalize_buffer(idx, path, basebuf.buf, basebuf.len, &basebuf) |
      renormalize_buffer(idx, path, sidebuf.buf, sidebuf.len, &sidebuf))
    ret = (basebuf.len == sidebuf.len &&
           !memcmp(basebuf.buf, sidebuf.buf, basebuf.len));

error_return:
  strbuf_release(&basebuf);
  strbuf_release(&sidebuf);
  return ret;
}

struct directory_versions {
  /*
   * versions: list of (basename -> version_info)
   *
   * The basenames are in reverse lexicographic order of full pathnames,
   * as processed in process_entries().  This puts all entries within
   * a directory together, and covers the directory itself after
   * everything within it, allowing us to write subtrees before needing
   * to record information for the tree itself.
   */
  struct string_list versions;

  /*
   * offsets: list of (full relative path directories -> integer offsets)
   *
   * Since versions contains basenames from files in multiple different
   * directories, we need to know which entries in versions correspond
   * to which directories.  Values of e.g.
   *     ""             0
   *     src            2
   *     src/moduleA    5
   * Would mean that entries 0-1 of versions are files in the toplevel
   * directory, entries 2-4 are files under src/, and the remaining
   * entries starting at index 5 are files under src/moduleA/.
   */
  struct string_list offsets;

  /*
   * last_directory: directory that previously processed file found in
   *
   * last_directory starts NULL, but records the directory in which the
   * previous file was found within.  As soon as
   *    directory(current_file) != last_directory
   * then we need to start updating accounting in versions & offsets.
   * Note that last_directory is always the last path in "offsets" (or
   * NULL if "offsets" is empty) so this exists just for quick access.
   */
  const char *last_directory;

  /* last_directory_len: cached computation of strlen(last_directory) */
  unsigned last_directory_len;
};

static int tree_entry_order(const void *a_, const void *b_)
{
  const struct string_list_item *a = a_;
  const struct string_list_item *b = b_;

  const struct merged_info *ami = a->util;
  const struct merged_info *bmi = b->util;
  return base_name_compare(a->string, strlen(a->string), ami->result.mode,
         b->string, strlen(b->string), bmi->result.mode);
}

static int write_tree(struct repository *repo,
          struct object_id *result_oid,
          struct string_list *versions,
          unsigned int offset)
{
  size_t maxlen = 0, extra;
  unsigned int nr;
  struct strbuf buf = STRBUF_INIT;
  int i, ret = 0;
  size_t hash_size = repo->hash_algo->rawsz;

  assert(offset <= versions->nr);
  nr = versions->nr - offset;
  if (versions->nr)
    /* No need for STABLE_QSORT -- filenames must be unique */
    QSORT(versions->items + offset, nr, tree_entry_order);

  /* Pre-allocate some space in buf */
  extra = hash_size + 8; /* 8: 6 for mode, 1 for space, 1 for NUL char */
  for (i = 0; i < nr; i++) {
    maxlen += strlen(versions->items[offset+i].string) + extra;
  }
  strbuf_grow(&buf, maxlen);

  /* Write each entry out to buf */
  for (i = 0; i < nr; i++) {
    struct merged_info *mi = versions->items[offset+i].util;
    struct version_info *ri = &mi->result;
    strbuf_addf(&buf, "%o %s%c",
          ri->mode,
          versions->items[offset+i].string, '\0');
    strbuf_add(&buf, ri->oid.hash, hash_size);
  }

  /* Write this object file out, and record in result_oid */
  if (odb_write_object(repo->objects, buf.buf,
           buf.len, OBJ_TREE, result_oid))
    ret = -1;
  strbuf_release(&buf);
  return ret;
}

static void record_entry_for_tree(struct directory_versions *dir_metadata,
          const char *path,
          struct merged_info *mi)
{
  const char *basename;

  if (mi->is_null)
    /* nothing to record */
    return;

  basename = path + mi->basename_offset;
  assert(strchr(basename, '/') == NULL);
  string_list_append(&dir_metadata->versions,
         basename)->util = &mi->result;
}

static int write_completed_directory(struct merge_options *opt,
             const char *new_directory_name,
             struct directory_versions *info)
{
  const char *prev_dir;
  struct merged_info *dir_info = NULL;
  unsigned int offset, ret = 0;

  /*
   * Some explanation of info->versions and info->offsets...
   *
   * process_entries() iterates over all relevant files AND
   * directories in reverse lexicographic order, and calls this
   * function.  Thus, an example of the paths that process_entries()
   * could operate on (along with the directories for those paths
   * being shown) is:
   *
   *     xtract.c             ""
   *     tokens.txt           ""
   *     src/moduleB/umm.c    src/moduleB
   *     src/moduleB/stuff.h  src/moduleB
   *     src/moduleB/baz.c    src/moduleB
   *     src/moduleB          src
   *     src/moduleA/foo.c    src/moduleA
   *     src/moduleA/bar.c    src/moduleA
   *     src/moduleA          src
   *     src                  ""
   *     Makefile             ""
   *
   * info->versions:
   *
   *     always contains the unprocessed entries and their
   *     version_info information.  For example, after the first five
   *     entries above, info->versions would be:
   *
   *         xtract.c     <xtract.c's version_info>
   *         token.txt    <token.txt's version_info>
   *         umm.c        <src/moduleB/umm.c's version_info>
   *         stuff.h      <src/moduleB/stuff.h's version_info>
   *         baz.c        <src/moduleB/baz.c's version_info>
   *
   *     Once a subdirectory is completed we remove the entries in
   *     that subdirectory from info->versions, writing it as a tree
   *     (write_tree()).  Thus, as soon as we get to src/moduleB,
   *     info->versions would be updated to
   *
   *         xtract.c     <xtract.c's version_info>
   *         token.txt    <token.txt's version_info>
   *         moduleB      <src/moduleB's version_info>
   *
   * info->offsets:
   *
   *     helps us track which entries in info->versions correspond to
   *     which directories.  When we are N directories deep (e.g. 4
   *     for src/modA/submod/subdir/), we have up to N+1 unprocessed
   *     directories (+1 because of toplevel dir).  Corresponding to
   *     the info->versions example above, after processing five entries
   *     info->offsets will be:
   *
   *         ""           0
   *         src/moduleB  2
   *
   *     which is used to know that xtract.c & token.txt are from the
   *     toplevel directory, while umm.c & stuff.h & baz.c are from the
   *     src/moduleB directory.  Again, following the example above,
   *     once we need to process src/moduleB, then info->offsets is
   *     updated to
   *
   *         ""           0
   *         src          2
   *
   *     which says that moduleB (and only moduleB so far) is in the
   *     src directory.
   *
   *     One unique thing to note about info->offsets here is that
   *     "src" was not added to info->offsets until there was a path
   *     (a file OR directory) immediately below src/ that got
   *     processed.
   *
   * Since process_entry() just appends new entries to info->versions,
   * write_completed_directory() only needs to do work if the next path
   * is in a directory that is different than the last directory found
   * in info->offsets.
   */

  /*
   * If we are working with the same directory as the last entry, there
   * is no work to do.  (See comments above the directory_name member of
   * struct merged_info for why we can use pointer comparison instead of
   * strcmp here.)
   */
  if (new_directory_name == info->last_directory)
    return 0;

  /*
   * If we are just starting (last_directory is NULL), or last_directory
   * is a prefix of the current directory, then we can just update
   * info->offsets to record the offset where we started this directory
   * and update last_directory to have quick access to it.
   */
  if (info->last_directory == NULL ||
      !strncmp(new_directory_name, info->last_directory,
         info->last_directory_len)) {
    uintptr_t offset = info->versions.nr;

    info->last_directory = new_directory_name;
    info->last_directory_len = strlen(info->last_directory);
    /*
     * Record the offset into info->versions where we will
     * start recording basenames of paths found within
     * new_directory_name.
     */
    string_list_append(&info->offsets,
           info->last_directory)->util = (void*)offset;
    return 0;
  }

  /*
   * The next entry that will be processed will be within
   * new_directory_name.  Since at this point we know that
   * new_directory_name is within a different directory than
   * info->last_directory, we have all entries for info->last_directory
   * in info->versions and we need to create a tree object for them.
   */
  dir_info = strmap_get(&opt->priv->paths, info->last_directory);
  assert(dir_info);
  offset = (uintptr_t)info->offsets.items[info->offsets.nr-1].util;
  if (offset == info->versions.nr) {
    /*
     * Actually, we don't need to create a tree object in this
     * case.  Whenever all files within a directory disappear
     * during the merge (e.g. unmodified on one side and
     * deleted on the other, or files were renamed elsewhere),
     * then we get here and the directory itself needs to be
     * omitted from its parent tree as well.
     */
    dir_info->is_null = 1;
  } else {
    /*
     * Write out the tree to the git object directory, and also
     * record the mode and oid in dir_info->result.
     */
    int record_tree = (!opt->mergeability_only ||
           opt->priv->call_depth);
    dir_info->is_null = 0;
    dir_info->result.mode = S_IFDIR;
    if (record_tree &&
        write_tree(opt->repo, &dir_info->result.oid, &info->versions,
             offset) < 0)
      ret = -1;
  }

  /*
   * We've now used several entries from info->versions and one entry
   * from info->offsets, so we get rid of those values.
   */
  info->offsets.nr--;
  info->versions.nr = offset;

  /*
   * Now we've taken care of the completed directory, but we need to
   * prepare things since future entries will be in
   * new_directory_name.  (In particular, process_entry() will be
   * appending new entries to info->versions.)  So, we need to make
   * sure new_directory_name is the last entry in info->offsets.
   */
  prev_dir = info->offsets.nr == 0 ? NULL :
       info->offsets.items[info->offsets.nr-1].string;
  if (new_directory_name != prev_dir) {
    uintptr_t c = info->versions.nr;
    string_list_append(&info->offsets,
           new_directory_name)->util = (void*)c;
  }

  /* And, of course, we need to update last_directory to match. */
  info->last_directory = new_directory_name;
  info->last_directory_len = strlen(info->last_directory);

  return ret;
}

/* Per entry merge function */
static int process_entry(struct merge_options *opt,
       const char *path,
       struct conflict_info *ci,
       struct directory_versions *dir_metadata)
{
  int df_file_index = 0;

  VERIFY_CI(ci);
  assert(ci->filemask >= 0 && ci->filemask <= 7);
  /* ci->match_mask == 7 was handled in collect_merge_info_callback() */
  assert(ci->match_mask == 0 || ci->match_mask == 3 ||
         ci->match_mask == 5 || ci->match_mask == 6);

  if (ci->dirmask) {
    record_entry_for_tree(dir_metadata, path, &ci->merged);
    if (ci->filemask == 0)
      /* nothing else to handle */
      return 0;
    assert(ci->df_conflict);
  }

  if (ci->df_conflict && ci->merged.result.mode == 0) {
    int i;

    /*
     * directory no longer in the way, but we do have a file we
     * need to place here so we need to clean away the "directory
     * merges to nothing" result.
     */
    ci->df_conflict = 0;
    assert(ci->filemask != 0);
    ci->merged.clean = 0;
    ci->merged.is_null = 0;
    /* and we want to zero out any directory-related entries */
    ci->match_mask = (ci->match_mask & ~ci->dirmask);
    ci->dirmask = 0;
    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
      if (ci->filemask & (1 << i))
        continue;
      ci->stages[i].mode = 0;
      oidcpy(&ci->stages[i].oid, null_oid(opt->repo->hash_algo));
    }
  } else if (ci->df_conflict && ci->merged.result.mode != 0) {
    /*
     * This started out as a D/F conflict, and the entries in
     * the competing directory were not removed by the merge as
     * evidenced by write_completed_directory() writing a value
     * to ci->merged.result.mode.
     */
    struct conflict_info *new_ci;
    const char *branch;
    const char *old_path = path;
    int i;

    assert(ci->merged.result.mode == S_IFDIR);

    /*
     * If filemask is 1, we can just ignore the file as having
     * been deleted on both sides.  We do not want to overwrite
     * ci->merged.result, since it stores the tree for all the
     * files under it.
     */
    if (ci->filemask == 1) {
      ci->filemask = 0;
      return 0;
    }

    /*
     * This file still exists on at least one side, and we want
     * the directory to remain here, so we need to move this
     * path to some new location.
     */
    new_ci = mem_pool_calloc(&opt->priv->pool, 1, sizeof(*new_ci));

    /* We don't really want new_ci->merged.result copied, but it'll
     * be overwritten below so it doesn't matter.  We also don't
     * want any directory mode/oid values copied, but we'll zero
     * those out immediately.  We do want the rest of ci copied.
     */
    memcpy(new_ci, ci, sizeof(*ci));
    new_ci->match_mask = (new_ci->match_mask & ~new_ci->dirmask);
    new_ci->dirmask = 0;
    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
      if (new_ci->filemask & (1 << i))
        continue;
      /* zero out any entries related to directories */
      new_ci->stages[i].mode = 0;
      oidcpy(&new_ci->stages[i].oid, null_oid(opt->repo->hash_algo));
    }

    /*
     * Find out which side this file came from; note that we
     * cannot just use ci->filemask, because renames could cause
     * the filemask to go back to 7.  So we use dirmask, then
     * pick the opposite side's index.
     */
    df_file_index = (ci->dirmask & (1 << 1)) ? 2 : 1;
    branch = (df_file_index == 1) ? opt->branch1 : opt->branch2;
    path = unique_path(opt, path, branch);
    strmap_put(&opt->priv->paths, path, new_ci);

    path_msg(opt, CONFLICT_FILE_DIRECTORY, 0,
       path, old_path, NULL, NULL,
       _("CONFLICT (file/directory): directory in the way "
         "of %s from %s; moving it to %s instead."),
       old_path, branch, path);

    /*
     * Zero out the filemask for the old ci.  At this point, ci
     * was just an entry for a directory, so we don't need to
     * do anything more with it.
     */
    ci->filemask = 0;

    /*
     * Now note that we're working on the new entry (path was
     * updated above.
     */
    ci = new_ci;
  }

  /*
   * NOTE: Below there is a long switch-like if-elseif-elseif... block
   *       which the code goes through even for the df_conflict cases
   *       above.
   */
  if (ci->match_mask) {
    ci->merged.clean = !ci->df_conflict && !ci->path_conflict;
    if (ci->match_mask == 6) {
      /* stages[1] == stages[2] */
      ci->merged.result.mode = ci->stages[1].mode;
      oidcpy(&ci->merged.result.oid, &ci->stages[1].oid);
    } else {
      /* determine the mask of the side that didn't match */
      unsigned int othermask = 7 & ~ci->match_mask;
      int side = (othermask == 4) ? 2 : 1;

      ci->merged.result.mode = ci->stages[side].mode;
      ci->merged.is_null = !ci->merged.result.mode;
      if (ci->merged.is_null)
        ci->merged.clean = 1;
      oidcpy(&ci->merged.result.oid, &ci->stages[side].oid);

      assert(othermask == 2 || othermask == 4);
      assert(ci->merged.is_null ==
             (ci->filemask == ci->match_mask));
    }
  } else if (ci->filemask >= 6 &&
       (S_IFMT & ci->stages[1].mode) !=
       (S_IFMT & ci->stages[2].mode)) {
    /* Two different items from (file/submodule/symlink) */
    if (opt->priv->call_depth) {
      /* Just use the version from the merge base */
      ci->merged.clean = 0;
      oidcpy(&ci->merged.result.oid, &ci->stages[0].oid);
      ci->merged.result.mode = ci->stages[0].mode;
      ci->merged.is_null = (ci->merged.result.mode == 0);
    } else {
      /* Handle by renaming one or both to separate paths. */
      unsigned o_mode = ci->stages[0].mode;
      unsigned a_mode = ci->stages[1].mode;
      unsigned b_mode = ci->stages[2].mode;
      struct conflict_info *new_ci;
      const char *a_path = NULL, *b_path = NULL;
      int rename_a = 0, rename_b = 0;

      new_ci = mem_pool_alloc(&opt->priv->pool,
            sizeof(*new_ci));

      if (S_ISREG(a_mode))
        rename_a = 1;
      else if (S_ISREG(b_mode))
        rename_b = 1;
      else {
        rename_a = 1;
        rename_b = 1;
      }

      if (rename_a)
        a_path = unique_path(opt, path, opt->branch1);
      if (rename_b)
        b_path = unique_path(opt, path, opt->branch2);

      if (rename_a && rename_b) {
        path_msg(opt, CONFLICT_DISTINCT_MODES, 0,
           path, a_path, b_path, NULL,
           _("CONFLICT (distinct types): %s had "
             "different types on each side; "
             "renamed both of them so each can "
             "be recorded somewhere."),
           path);
      } else {
        path_msg(opt, CONFLICT_DISTINCT_MODES, 0,
           path, rename_a ? a_path : b_path,
           NULL, NULL,
           _("CONFLICT (distinct types): %s had "
             "different types on each side; "
             "renamed one of them so each can be "
             "recorded somewhere."),
           path);
      }

      ci->merged.clean = 0;
      memcpy(new_ci, ci, sizeof(*new_ci));

      /* Put b into new_ci, removing a from stages */
      new_ci->merged.result.mode = ci->stages[2].mode;
      oidcpy(&new_ci->merged.result.oid, &ci->stages[2].oid);
      new_ci->stages[1].mode = 0;
      oidcpy(&new_ci->stages[1].oid, null_oid(opt->repo->hash_algo));
      new_ci->filemask = 5;
      if ((S_IFMT & b_mode) != (S_IFMT & o_mode)) {
        new_ci->stages[0].mode = 0;
        oidcpy(&new_ci->stages[0].oid, null_oid(opt->repo->hash_algo));
        new_ci->filemask = 4;
      }

      /* Leave only a in ci, fixing stages. */
      ci->merged.result.mode = ci->stages[1].mode;
      oidcpy(&ci->merged.result.oid, &ci->stages[1].oid);
      ci->stages[2].mode = 0;
      oidcpy(&ci->stages[2].oid, null_oid(opt->repo->hash_algo));
      ci->filemask = 3;
      if ((S_IFMT & a_mode) != (S_IFMT & o_mode)) {
        ci->stages[0].mode = 0;
        oidcpy(&ci->stages[0].oid, null_oid(opt->repo->hash_algo));
        ci->filemask = 2;
      }

      /* Insert entries into opt->priv_paths */
      assert(rename_a || rename_b);
      if (rename_a)
        strmap_put(&opt->priv->paths, a_path, ci);

      if (!rename_b)
        b_path = path;
      strmap_put(&opt->priv->paths, b_path, new_ci);

      if (rename_a && rename_b)
        strmap_remove(&opt->priv->paths, path, 0);

      /*
       * Do special handling for b_path since process_entry()
       * won't be called on it specially.
       */
      strmap_put(&opt->priv->conflicted, b_path, new_ci);
      record_entry_for_tree(dir_metadata, b_path,
                &new_ci->merged);

      /*
       * Remaining code for processing this entry should
       * think in terms of processing a_path.
       */
      if (a_path)
        path = a_path;
    }
  } else if (ci->filemask >= 6) {
    /* Need a two-way or three-way content merge */
    struct version_info merged_file;
    int clean_merge;
    struct version_info *o = &ci->stages[0];
    struct version_info *a = &ci->stages[1];
    struct version_info *b = &ci->stages[2];
    int record_object = (!opt->mergeability_only ||
             opt->priv->call_depth);

    clean_merge = handle_content_merge(opt, path, o, a, b,
               ci->pathnames,
               opt->priv->call_depth * 2,
               record_object,
               &merged_file);
    if (clean_merge < 0)
      return -1;
    ci->merged.clean = clean_merge &&
           !ci->df_conflict && !ci->path_conflict;
    ci->merged.result.mode = merged_file.mode;
    ci->merged.is_null = (merged_file.mode == 0);
    oidcpy(&ci->merged.result.oid, &merged_file.oid);
    if (clean_merge && ci->df_conflict) {
      assert(df_file_index == 1 || df_file_index == 2);
      ci->filemask = 1 << df_file_index;
      ci->stages[df_file_index].mode = merged_file.mode;
      oidcpy(&ci->stages[df_file_index].oid, &merged_file.oid);
    }
    if (!clean_merge) {
      const char *reason = _("content");
      if (ci->filemask == 6)
        reason = _("add/add");
      if (S_ISGITLINK(merged_file.mode))
        reason = _("submodule");
      path_msg(opt, CONFLICT_CONTENTS, 0,
         path, NULL, NULL, NULL,
         _("CONFLICT (%s): Merge conflict in %s"),
         reason, path);
    }
  } else if (ci->filemask == 3 || ci->filemask == 5) {
    /* Modify/delete */
    const char *modify_branch, *delete_branch;
    int side = (ci->filemask == 5) ? 2 : 1;
    int index = opt->priv->call_depth ? 0 : side;

    ci->merged.result.mode = ci->stages[index].mode;
    oidcpy(&ci->merged.result.oid, &ci->stages[index].oid);
    ci->merged.clean = 0;

    modify_branch = (side == 1) ? opt->branch1 : opt->branch2;
    delete_branch = (side == 1) ? opt->branch2 : opt->branch1;

    if (opt->renormalize &&
        blob_unchanged(opt, &ci->stages[0], &ci->stages[side],
           path)) {
      if (!ci->path_conflict) {
        /*
         * Blob unchanged after renormalization, so
         * there's no modify/delete conflict after all;
         * we can just remove the file.
         */
        ci->merged.is_null = 1;
        ci->merged.clean = 1;
         /*
          * file goes away => even if there was a
          * directory/file conflict there isn't one now.
          */
        ci->df_conflict = 0;
      } else {
        /* rename/delete, so conflict remains */
      }
    } else if (ci->path_conflict &&
         oideq(&ci->stages[0].oid, &ci->stages[side].oid)) {
      /*
       * This came from a rename/delete; no action to take,
       * but avoid printing "modify/delete" conflict notice
       * since the contents were not modified.
       */
    } else {
      path_msg(opt, CONFLICT_MODIFY_DELETE, 0,
         path, NULL, NULL, NULL,
         _("CONFLICT (modify/delete): %s deleted in %s "
           "and modified in %s.  Version %s of %s left "
           "in tree."),
         path, delete_branch, modify_branch,
         modify_branch, path);
    }
  } else if (ci->filemask == 2 || ci->filemask == 4) {
    /* Added on one side */
    int side = (ci->filemask == 4) ? 2 : 1;
    ci->merged.result.mode = ci->stages[side].mode;
    oidcpy(&ci->merged.result.oid, &ci->stages[side].oid);
    ci->merged.clean = !ci->df_conflict && !ci->path_conflict;
  } else if (ci->filemask == 1) {
    /* Deleted on both sides */
    ci->merged.is_null = 1;
    ci->merged.result.mode = 0;
    oidcpy(&ci->merged.result.oid, null_oid(opt->repo->hash_algo));
    assert(!ci->df_conflict);
    ci->merged.clean = !ci->path_conflict;
  }

  /*
   * If still conflicted, record it separately.  This allows us to later
   * iterate over just conflicted entries when updating the index instead
   * of iterating over all entries.
   */
  if (!ci->merged.clean)
    strmap_put(&opt->priv->conflicted, path, ci);

  /* Record metadata for ci->merged in dir_metadata */
  record_entry_for_tree(dir_metadata, path, &ci->merged);
  return 0;
}

static void prefetch_for_content_merges(struct merge_options *opt,
          struct string_list *plist)
{
  struct string_list_item *e;
  struct oid_array to_fetch = OID_ARRAY_INIT;

  if (!repo_has_promisor_remote(opt->repo))
    return;

  for (e = &plist->items[plist->nr-1]; e >= plist->items; --e) {
    /* char *path = e->string; */
    struct conflict_info *ci = e->util;
    int i;

    /* Ignore clean entries */
    if (ci->merged.clean)
      continue;

    /* Ignore entries that don't need a content merge */
    if (ci->match_mask || ci->filemask < 6 ||
        !S_ISREG(ci->stages[1].mode) ||
        !S_ISREG(ci->stages[2].mode) ||
        oideq(&ci->stages[1].oid, &ci->stages[2].oid))
      continue;

    /* Also don't need content merge if base matches either side */
    if (ci->filemask == 7 &&
        S_ISREG(ci->stages[0].mode) &&
        (oideq(&ci->stages[0].oid, &ci->stages[1].oid) ||
         oideq(&ci->stages[0].oid, &ci->stages[2].oid)))
      continue;

    for (i = 0; i < 3; i++) {
      unsigned side_mask = (1 << i);
      struct version_info *vi = &ci->stages[i];

      if ((ci->filemask & side_mask) &&
          S_ISREG(vi->mode) &&
          odb_read_object_info_extended(opt->repo->objects, &vi->oid, NULL,
                OBJECT_INFO_FOR_PREFETCH))
        oid_array_append(&to_fetch, &vi->oid);
    }
  }

  promisor_remote_get_direct(opt->repo, to_fetch.oid, to_fetch.nr);
  oid_array_clear(&to_fetch);
}

static int process_entries(struct merge_options *opt,
         struct object_id *result_oid)
{
  struct hashmap_iter iter;
  struct strmap_entry *e;
  struct string_list plist = STRING_LIST_INIT_NODUP;
  struct string_list_item *entry;
  struct directory_versions dir_metadata = { STRING_LIST_INIT_NODUP,
               STRING_LIST_INIT_NODUP,
               NULL, 0 };
  int ret = 0;
  const int record_tree = (!opt->mergeability_only ||
         opt->priv->call_depth);

  trace2_region_enter("merge", "process_entries setup", opt->repo);
  if (strmap_empty(&opt->priv->paths)) {
    oidcpy(result_oid, opt->repo->hash_algo->empty_tree);
    return 0;
  }

  /* Hack to pre-allocate plist to the desired size */
  trace2_region_enter("merge", "plist grow", opt->repo);
  ALLOC_GROW(plist.items, strmap_get_size(&opt->priv->paths), plist.alloc);
  trace2_region_leave("merge", "plist grow", opt->repo);

  /* Put every entry from paths into plist, then sort */
  trace2_region_enter("merge", "plist copy", opt->repo);
  strmap_for_each_entry(&opt->priv->paths, &iter, e) {
    string_list_append(&plist, e->key)->util = e->value;
  }
  trace2_region_leave("merge", "plist copy", opt->repo);

  trace2_region_enter("merge", "plist special sort", opt->repo);
  plist.cmp = sort_dirs_next_to_their_children;
  string_list_sort(&plist);
  trace2_region_leave("merge", "plist special sort", opt->repo);

  trace2_region_leave("merge", "process_entries setup", opt->repo);

  /*
   * Iterate over the items in reverse order, so we can handle paths
   * below a directory before needing to handle the directory itself.
   *
   * This allows us to write subtrees before we need to write trees,
   * and it also enables sane handling of directory/file conflicts
   * (because it allows us to know whether the directory is still in
   * the way when it is time to process the file at the same path).
   */
  trace2_region_enter("merge", "processing", opt->repo);
  prefetch_for_content_merges(opt, &plist);
  for (entry = &plist.items[plist.nr-1]; entry >= plist.items; --entry) {
    char *path = entry->string;
    /*
     * NOTE: mi may actually be a pointer to a conflict_info, but
     * we have to check mi->clean first to see if it's safe to
     * reassign to such a pointer type.
     */
    struct merged_info *mi = entry->util;

    if (write_completed_directory(opt, mi->directory_name,
                &dir_metadata) < 0) {
      ret = -1;
      goto cleanup;
    }
    if (mi->clean)
      record_entry_for_tree(&dir_metadata, path, mi);
    else {
      struct conflict_info *ci = (struct conflict_info *)mi;
      if (process_entry(opt, path, ci, &dir_metadata) < 0) {
        ret = -1;
        goto cleanup;
      };
      if (!ci->merged.clean && opt->mergeability_only &&
          !opt->priv->call_depth) {
        ret = 0;
        goto cleanup;
      }

    }
  }
  trace2_region_leave("merge", "processing", opt->repo);

  trace2_region_enter("merge", "process_entries cleanup", opt->repo);
  if (dir_metadata.offsets.nr != 1 ||
      (uintptr_t)dir_metadata.offsets.items[0].util != 0) {
    printf("dir_metadata.offsets.nr = %"PRIuMAX" (should be 1)\n",
           (uintmax_t)dir_metadata.offsets.nr);
    printf("dir_metadata.offsets.items[0].util = %u (should be 0)\n",
           (unsigned)(uintptr_t)dir_metadata.offsets.items[0].util);
    fflush(stdout);
    BUG("dir_metadata accounting completely off; shouldn't happen");
  }
  if (record_tree &&
      write_tree(opt->repo, result_oid, &dir_metadata.versions, 0) < 0)
    ret = -1;
cleanup:
  string_list_clear(&plist, 0);
  string_list_clear(&dir_metadata.versions, 0);
  string_list_clear(&dir_metadata.offsets, 0);
  trace2_region_leave("merge", "process_entries cleanup", opt->repo);

  return ret;
}

/*** Function Grouping: functions related to merge_switch_to_result() ***/

static int checkout(struct merge_options *opt,
        struct tree *prev,
        struct tree *next)
{
  /* Switch the index/working copy from old to new */
  int ret;
  struct tree_desc trees[2];
  struct unpack_trees_options unpack_opts;

  memset(&unpack_opts, 0, sizeof(unpack_opts));
  unpack_opts.head_idx = -1;
  unpack_opts.src_index = opt->repo->index;
  unpack_opts.dst_index = opt->repo->index;

  setup_unpack_trees_porcelain(&unpack_opts, "merge");

  /*
   * NOTE: if this were just "git checkout" code, we would probably
   * read or refresh the cache and check for a conflicted index, but
   * builtin/merge.c or sequencer.c really needs to read the index
   * and check for conflicted entries before starting merging for a
   * good user experience (no sense waiting for merges/rebases before
   * erroring out), so there's no reason to duplicate that work here.
   */

  /* 2-way merge to the new branch */
  unpack_opts.update = 1;
  unpack_opts.merge = 1;
  unpack_opts.quiet = 0; /* FIXME: sequencer might want quiet? */
  unpack_opts.verbose_update = (opt->verbosity > 2);
  unpack_opts.fn = twoway_merge;
  unpack_opts.preserve_ignored = 0; /* FIXME: !opts->overwrite_ignore */
  if (repo_parse_tree(opt->repo, prev) < 0)
    return -1;
  init_tree_desc(&trees[0], &prev->object.oid, prev->buffer, prev->size);
  if (repo_parse_tree(opt->repo, next) < 0)
    return -1;
  init_tree_desc(&trees[1], &next->object.oid, next->buffer, next->size);

  ret = unpack_trees(2, trees, &unpack_opts);
  clear_unpack_trees_porcelain(&unpack_opts);
  return ret;
}

static int record_conflicted_index_entries(struct merge_options *opt)
{
  struct hashmap_iter iter;
  struct strmap_entry *e;
  struct index_state *index = opt->repo->index;
  struct checkout state = CHECKOUT_INIT;
  int errs = 0;
  int original_cache_nr;

  if (strmap_empty(&opt->priv->conflicted))
    return 0;

  /*
   * We are in a conflicted state. These conflicts might be inside
   * sparse-directory entries, so check if any entries are outside
   * of the sparse-checkout cone preemptively.
   *
   * We set original_cache_nr below, but that might change if
   * index_name_pos() calls ask for paths within sparse directories.
   */
  strmap_for_each_entry(&opt->priv->conflicted, &iter, e) {
    if (!path_in_sparse_checkout(e->key, index)) {
      ensure_full_index(index);
      break;
    }
  }

  /* If any entries have skip_worktree set, we'll have to check 'em out */
  state.force = 1;
  state.quiet = 1;
  state.refresh_cache = 1;
  state.istate = index;
  original_cache_nr = index->cache_nr;

  /* Append every entry from conflicted into index, then sort */
  strmap_for_each_entry(&opt->priv->conflicted, &iter, e) {
    const char *path = e->key;
    struct conflict_info *ci = e->value;
    int pos;
    struct cache_entry *ce;
    int i;

    VERIFY_CI(ci);

    /*
     * The index will already have a stage=0 entry for this path,
     * because we created an as-merged-as-possible version of the
     * file and checkout() moved the working copy and index over
     * to that version.
     *
     * However, previous iterations through this loop will have
     * added unstaged entries to the end of the cache which
     * ignore the standard alphabetical ordering of cache
     * entries and break invariants needed for index_name_pos()
     * to work.  However, we know the entry we want is before
     * those appended cache entries, so do a temporary swap on
     * cache_nr to only look through entries of interest.
     */
    SWAP(index->cache_nr, original_cache_nr);
    pos = index_name_pos(index, path, strlen(path));
    SWAP(index->cache_nr, original_cache_nr);
    if (pos < 0) {
      if (ci->filemask != 1)
        BUG("Conflicted %s but nothing in basic working tree or index; this shouldn't happen", path);
      cache_tree_invalidate_path(index, path);
    } else {
      ce = index->cache[pos];

      /*
       * Clean paths with CE_SKIP_WORKTREE set will not be
       * written to the working tree by the unpack_trees()
       * call in checkout().  Our conflicted entries would
       * have appeared clean to that code since we ignored
       * the higher order stages.  Thus, we need override
       * the CE_SKIP_WORKTREE bit and manually write those
       * files to the working disk here.
       */
      if (ce_skip_worktree(ce))
        errs |= checkout_entry(ce, &state, NULL, NULL);

      /*
       * Mark this cache entry for removal and instead add
       * new stage>0 entries corresponding to the
       * conflicts.  If there are many conflicted entries, we
       * want to avoid memmove'ing O(NM) entries by
       * inserting the new entries one at a time.  So,
       * instead, we just add the new cache entries to the
       * end (ignoring normal index requirements on sort
       * order) and sort the index once we're all done.
       */
      ce->ce_flags |= CE_REMOVE;
    }

    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
      struct version_info *vi;
      if (!(ci->filemask & (1ul << i)))
        continue;
      vi = &ci->stages[i];
      ce = make_cache_entry(index, vi->mode, &vi->oid,
                path, i+1, 0);
      add_index_entry(index, ce, ADD_CACHE_JUST_APPEND);
    }
  }

  /*
   * Remove the unused cache entries (and invalidate the relevant
   * cache-trees), then sort the index entries to get the conflicted
   * entries we added to the end into their right locations.
   */
  remove_marked_cache_entries(index, 1);
  /*
   * No need for STABLE_QSORT -- cmp_cache_name_compare sorts primarily
   * on filename and secondarily on stage, and (name, stage #) are a
   * unique tuple.
   */
  QSORT(index->cache, index->cache_nr, cmp_cache_name_compare);

  return errs;
}

static void print_submodule_conflict_suggestion(struct string_list *csub) {
  struct string_list_item *item;
  struct strbuf msg = STRBUF_INIT;
  struct strbuf tmp = STRBUF_INIT;
  struct strbuf subs = STRBUF_INIT;

  if (!csub->nr)
    return;

  strbuf_add_separated_string_list(&subs, " ", csub);
  for_each_string_list_item(item, csub) {
    struct conflicted_submodule_item *util = item->util;

    /*
     * NEEDSWORK: The steps to resolve these errors deserve a more
     * detailed explanation than what is currently printed below.
     */
    if (util->flag == CONFLICT_SUBMODULE_NOT_INITIALIZED ||
        util->flag == CONFLICT_SUBMODULE_HISTORY_NOT_AVAILABLE)
      continue;

    /*
     * TRANSLATORS: This is a line of advice to resolve a merge
     * conflict in a submodule. The first argument is the submodule
     * name, and the second argument is the abbreviated id of the
     * commit that needs to be merged.  For example:
     *  - go to submodule (mysubmodule), and either merge commit abc1234"
     */
    strbuf_addf(&tmp, _(" - go to submodule (%s), and either merge commit %s\n"
            "   or update to an existing commit which has merged those changes\n"),
          item->string, util->abbrev);
  }

  /*
   * TRANSLATORS: This is a detailed message for resolving submodule
   * conflicts.  The first argument is string containing one step per
   * submodule.  The second is a space-separated list of submodule names.
   */
  strbuf_addf(&msg,
        _("Recursive merging with submodules currently only supports trivial cases.\n"
          "Please manually handle the merging of each conflicted submodule.\n"
          "This can be accomplished with the following steps:\n"
          "%s"
          " - come back to superproject and run:\n\n"
          "      git add %s\n\n"
          "   to record the above merge or update\n"
          " - resolve any other conflicts in the superproject\n"
          " - commit the resulting index in the superproject\n"),
        tmp.buf, subs.buf);

  advise_if_enabled(ADVICE_SUBMODULE_MERGE_CONFLICT, "%s", msg.buf);

  strbuf_release(&subs);
  strbuf_release(&tmp);
  strbuf_release(&msg);
}

void merge_display_update_messages(struct merge_options *opt,
           int detailed,
           struct merge_result *result)
{
  struct merge_options_internal *opti = result->priv;
  struct hashmap_iter iter;
  struct strmap_entry *e;
  struct string_list olist = STRING_LIST_INIT_NODUP;
  FILE *o = stdout;

  if (opt->record_conflict_msgs_as_headers)
    BUG("Either display conflict messages or record them as headers, not both");
  if (opt->mergeability_only)
    BUG("Displaying conflict messages incompatible with mergeability-only checks");

  trace2_region_enter("merge", "display messages", opt->repo);

  /* Hack to pre-allocate olist to the desired size */
  ALLOC_GROW(olist.items, strmap_get_size(&opti->conflicts),
       olist.alloc);

  /* Put every entry from output into olist, then sort */
  strmap_for_each_entry(&opti->conflicts, &iter, e) {
    string_list_append(&olist, e->key)->util = e->value;
  }
  string_list_sort(&olist);

  /* Print to stderr if we hit errors rather than just conflicts */
  if (result->clean < 0)
    o = stderr;

  /* Iterate over the items, printing them */
  for (int path_nr = 0; path_nr < olist.nr; ++path_nr) {
    struct string_list *conflicts = olist.items[path_nr].util;
    for (int i = 0; i < conflicts->nr; i++) {
      struct logical_conflict_info *info =
        conflicts->items[i].util;

      /* On failure, ignore regular conflict types */
      if (result->clean < 0 &&
          info->type < NB_REGULAR_CONFLICT_TYPES)
        continue;

      if (detailed) {
        fprintf(o, "%lu", (unsigned long)info->paths.nr);
        fputc('\0', o);
        for (int n = 0; n < info->paths.nr; n++) {
          fputs(info->paths.v[n], o);
          fputc('\0', o);
        }
        fputs(type_short_descriptions[info->type], o);
        fputc('\0', o);
      }
      fputs(conflicts->items[i].string, o);
      fputc('\n', o);
      if (detailed)
        fputc('\0', o);
    }
  }
  string_list_clear(&olist, 0);

  if (result->clean >= 0)
    print_submodule_conflict_suggestion(&opti->conflicted_submodules);

  /* Also include needed rename limit adjustment now */
  diff_warn_rename_limit("merge.renamelimit",
             opti->renames.needed_limit, 0);

  trace2_region_leave("merge", "display messages", opt->repo);
}

void merge_get_conflicted_files(struct merge_result *result,
        struct string_list *conflicted_files)
{
  struct hashmap_iter iter;
  struct strmap_entry *e;
  struct merge_options_internal *opti = result->priv;

  strmap_for_each_entry(&opti->conflicted, &iter, e) {
    const char *path = e->key;
    struct conflict_info *ci = e->value;
    int i;

    VERIFY_CI(ci);

    for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
      struct stage_info *si;

      if (!(ci->filemask & (1ul << i)))
        continue;

      si = xmalloc(sizeof(*si));
      si->stage = i+1;
      si->mode = ci->stages[i].mode;
      oidcpy(&si->oid, &ci->stages[i].oid);
      string_list_append(conflicted_files, path)->util = si;
    }
  }
  /* string_list_sort() uses a stable sort, so we're good */
  string_list_sort(conflicted_files);
}

void merge_switch_to_result(struct merge_options *opt,
          struct tree *head,
          struct merge_result *result,
          int update_worktree_and_index,
          int display_update_msgs)
{
  assert(opt->priv == NULL);
  if (result->clean >= 0 && update_worktree_and_index) {
    trace2_region_enter("merge", "checkout", opt->repo);
    if (checkout(opt, head, result->tree)) {
      /* failure to function */
      result->clean = -1;
      merge_finalize(opt, result);
      trace2_region_leave("merge", "checkout", opt->repo);
      return;
    }
    trace2_region_leave("merge", "checkout", opt->repo);

    trace2_region_enter("merge", "record_conflicted", opt->repo);
    opt->priv = result->priv;
    if (record_conflicted_index_entries(opt)) {
      /* failure to function */
      opt->priv = NULL;
      result->clean = -1;
      merge_finalize(opt, result);
      trace2_region_leave("merge", "record_conflicted",
              opt->repo);
      return;
    }
    opt->priv = NULL;
    trace2_region_leave("merge", "record_conflicted", opt->repo);

    trace2_region_enter("merge", "write_auto_merge", opt->repo);
    if (refs_update_ref(get_main_ref_store(opt->repo), "", "AUTO_MERGE",
            &result->tree->object.oid, NULL, REF_NO_DEREF,
            UPDATE_REFS_MSG_ON_ERR)) {
      /* failure to function */
      opt->priv = NULL;
      result->clean = -1;
      merge_finalize(opt, result);
      trace2_region_leave("merge", "write_auto_merge",
              opt->repo);
      return;
    }
    trace2_region_leave("merge", "write_auto_merge", opt->repo);
  }
  if (display_update_msgs)
    merge_display_update_messages(opt, /* detailed */ 0, result);

  merge_finalize(opt, result);
}

void merge_finalize(struct merge_options *opt,
        struct merge_result *result)
{
  if (opt->renormalize)
    git_attr_set_direction(GIT_ATTR_CHECKIN);
  assert(opt->priv == NULL);

  if (result->priv) {
    clear_or_reinit_internal_opts(result->priv, 0);
    FREE_AND_NULL(result->priv);
  }
}

/*** Function Grouping: helper functions for merge_incore_*() ***/

static struct tree *shift_tree_object(struct repository *repo,
              struct tree *one, struct tree *two,
              const char *subtree_shift)
{
  struct object_id shifted;

  if (!*subtree_shift) {
    shift_tree(repo, &one->object.oid, &two->object.oid, &shifted, 0);
  } else {
    shift_tree_by(repo, &one->object.oid, &two->object.oid, &shifted,
            subtree_shift);
  }
  if (oideq(&two->object.oid, &shifted))
    return two;
  return lookup_tree(repo, &shifted);
}

static inline void set_commit_tree(struct commit *c, struct tree *t)
{
  c->maybe_tree = t;
}

struct commit *make_virtual_commit(struct repository *repo,
           struct tree *tree,
           const char *comment)
{
  struct commit *commit = alloc_commit_node(repo);

  set_merge_remote_desc(commit, comment, (struct object *)commit);
  set_commit_tree(commit, tree);
  commit->object.parsed = 1;
  return commit;
}

static void merge_start(struct merge_options *opt, struct merge_result *result)
{
  struct rename_info *renames;
  int i;
  struct mem_pool *pool = NULL;

  /* Sanity checks on opt */
  trace2_region_enter("merge", "sanity checks", opt->repo);
  assert(opt->repo);

  assert(opt->branch1 && opt->branch2);

  assert(opt->detect_directory_renames >= MERGE_DIRECTORY_RENAMES_NONE &&
         opt->detect_directory_renames <= MERGE_DIRECTORY_RENAMES_TRUE);
  assert(opt->rename_limit >= -1);
  assert(opt->rename_score >= 0 && opt->rename_score <= MAX_SCORE);
  assert(opt->show_rename_progress >= 0 && opt->show_rename_progress <= 1);

  assert(opt->xdl_opts >= 0);
  assert(opt->recursive_variant >= MERGE_VARIANT_NORMAL &&
         opt->recursive_variant <= MERGE_VARIANT_THEIRS);

  if (opt->msg_header_prefix)
    assert(opt->record_conflict_msgs_as_headers);

  /*
   * detect_renames, verbosity, buffer_output, and obuf are ignored
   * fields that were used by "recursive" rather than "ort" -- but
   * sanity check them anyway.
   */
  assert(opt->detect_renames >= -1 &&
         opt->detect_renames <= DIFF_DETECT_COPY);
  assert(opt->verbosity >= 0 && opt->verbosity <= 5);
  assert(opt->buffer_output <= 2);
  assert(opt->obuf.len == 0);

  assert(opt->priv == NULL);
  if (result->_properly_initialized != 0 &&
      result->_properly_initialized != RESULT_INITIALIZED)
    BUG("struct merge_result passed to merge_incore_*recursive() must be zeroed or filled with values from a previous run");
  assert(!!result->priv == !!result->_properly_initialized);
  if (result->priv) {
    opt->priv = result->priv;
    result->priv = NULL;
    /*
     * opt->priv non-NULL means we had results from a previous
     * run; do a few sanity checks that user didn't mess with
     * it in an obvious fashion.
     */
    assert(opt->priv->call_depth == 0);
    assert(!opt->priv->toplevel_dir ||
           0 == strlen(opt->priv->toplevel_dir));
  }
  trace2_region_leave("merge", "sanity checks", opt->repo);

  /* Handle attr direction stuff for renormalization */
  if (opt->renormalize)
    git_attr_set_direction(GIT_ATTR_CHECKOUT);

  /* Initialization of opt->priv, our internal merge data */
  trace2_region_enter("merge", "allocate/init", opt->repo);
  if (opt->priv) {
    clear_or_reinit_internal_opts(opt->priv, 1);
    string_list_init_nodup(&opt->priv->conflicted_submodules);
    trace2_region_leave("merge", "allocate/init", opt->repo);
    return;
  }
  opt->priv = xcalloc(1, sizeof(*opt->priv));

  /* Initialization of various renames fields */
  renames = &opt->priv->renames;
  mem_pool_init(&opt->priv->pool, 0);
  pool = &opt->priv->pool;
  for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++) {
    strintmap_init_with_options(&renames->dirs_removed[i],
              NOT_RELEVANT, pool, 0);
    strmap_init_with_options(&renames->dir_rename_count[i],
           NULL, 1);
    strmap_init_with_options(&renames->dir_renames[i],
           NULL, 0);
    /*
     * relevant_sources uses -1 for the default, because we need
     * to be able to distinguish not-in-strintmap from valid
     * relevant_source values from enum file_rename_relevance.
     * In particular, possibly_cache_new_pair() expects a negative
     * value for not-found entries.
     */
    strintmap_init_with_options(&renames->relevant_sources[i],
              -1 /* explicitly invalid */,
              pool, 0);
    strmap_init_with_options(&renames->cached_pairs[i],
           NULL, 1);
    strset_init_with_options(&renames->cached_irrelevant[i],
           NULL, 1);
    strset_init_with_options(&renames->cached_target_names[i],
           NULL, 0);
  }
  for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++) {
    strintmap_init_with_options(&renames->deferred[i].possible_trivial_merges,
              0, pool, 0);
    strset_init_with_options(&renames->deferred[i].target_dirs,
           pool, 1);
    renames->deferred[i].trivial_merges_okay = 1; /* 1 == maybe */
  }

  /*
   * Although we initialize opt->priv->paths with strdup_strings=0,
   * that's just to avoid making yet another copy of an allocated
   * string.  Putting the entry into paths means we are taking
   * ownership, so we will later free it.
   *
   * In contrast, conflicted just has a subset of keys from paths, so
   * we don't want to free those (it'd be a duplicate free).
   */
  strmap_init_with_options(&opt->priv->paths, pool, 0);
  strmap_init_with_options(&opt->priv->conflicted, pool, 0);

  /*
   * keys & string_lists in conflicts will sometimes need to outlive
   * "paths", so it will have a copy of relevant keys.  It's probably
   * a small subset of the overall paths that have special output.
   */
  strmap_init(&opt->priv->conflicts);

  trace2_region_leave("merge", "allocate/init", opt->repo);
}

static void merge_check_renames_reusable(struct merge_options *opt,
           struct merge_result *result,
           struct tree *merge_base,
           struct tree *side1,
           struct tree *side2)
{
  struct rename_info *renames;
  struct tree **merge_trees;
  struct merge_options_internal *opti = result->priv;

  if (!opti)
    return;

  renames = &opti->renames;
  merge_trees = renames->merge_trees;

  /*
   * Handle case where previous merge operation did not want cache to
   * take effect, e.g. because rename/rename(1to1) makes it invalid.
   */
  if (!merge_trees[0]) {
    assert(!merge_trees[0] && !merge_trees[1] && !merge_trees[2]);
    renames->cached_pairs_valid_side = 0; /* neither side valid */
    return;
  }

  /*
   * Avoid using cached renames when directory rename detection is
   * turned off.  Cached renames are far less important in that case,
   * and they lead to testcases with an interesting intersection of
   * effects from relevant renames optimization, trivial directory
   * resolution optimization, and cached renames all converging when
   * the target of a cached rename is in a directory that
   * collect_merge_info() does not recurse into.  To avoid such
   * problems, simply disable cached renames for this case (similar
   * to the rename/rename(1to1) case; see the "disabling the
   * optimization" comment near that case).
   *
   * This could be revisited in the future; see the commit message
   * where this comment was added for some possible pointers, or the
   * later commit where this comment was added.
   */
  if (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_NONE) {
    renames->cached_pairs_valid_side = 0; /* neither side valid */
    return;
  }

  /*
   * Handle other cases; note that merge_trees[0..2] will only
   * be NULL if opti is, or if all three were manually set to
   * NULL by e.g. rename/rename(1to1) handling.
   */
  assert(merge_trees[0] && merge_trees[1] && merge_trees[2]);

  /* Check if we meet a condition for re-using cached_pairs */
  if (oideq(&merge_base->object.oid, &merge_trees[2]->object.oid) &&
      oideq(&side1->object.oid, &result->tree->object.oid))
    renames->cached_pairs_valid_side = MERGE_SIDE1;
  else if (oideq(&merge_base->object.oid, &merge_trees[1]->object.oid) &&
     oideq(&side2->object.oid, &result->tree->object.oid))
    renames->cached_pairs_valid_side = MERGE_SIDE2;
  else
    renames->cached_pairs_valid_side = 0; /* neither side valid */
}

/*** Function Grouping: merge_incore_*() and their internal variants ***/

static void move_opt_priv_to_result_priv(struct merge_options *opt,
           struct merge_result *result)
{
  /*
   * opt->priv and result->priv are a bit weird.  opt->priv contains
   * information that we can re-use in subsequent merge operations to
   * enable our cached renames optimization.  The best way to provide
   * that to subsequent merges is putting it in result->priv.
   * However, putting it directly there would mean retrofitting lots
   * of functions in this file to also take a merge_result pointer,
   * which is ugly and annoying.  So, we just make sure at the end of
   * the merge (the outer merge if there are internal recursive ones)
   * to move it.
   */
  assert(opt->priv && !result->priv);
  result->priv = opt->priv;
  result->_properly_initialized = RESULT_INITIALIZED;
  opt->priv = NULL;
}

/*
 * Originally from merge_trees_internal(); heavily adapted, though.
 */
static void merge_ort_nonrecursive_internal(struct merge_options *opt,
              struct tree *merge_base,
              struct tree *side1,
              struct tree *side2,
              struct merge_result *result)
{
  struct object_id working_tree_oid;

  if (opt->subtree_shift) {
    side2 = shift_tree_object(opt->repo, side1, side2,
            opt->subtree_shift);
    merge_base = shift_tree_object(opt->repo, side1, merge_base,
                 opt->subtree_shift);
  }

redo:
  trace2_region_enter("merge", "collect_merge_info", opt->repo);
  if (collect_merge_info(opt, merge_base, side1, side2) != 0) {
    /*
     * TRANSLATORS: The %s arguments are: 1) tree hash of a merge
     * base, and 2-3) the trees for the two trees we're merging.
     */
    error(_("collecting merge info failed for trees %s, %s, %s"),
        oid_to_hex(&merge_base->object.oid),
        oid_to_hex(&side1->object.oid),
        oid_to_hex(&side2->object.oid));
    result->clean = -1;
    move_opt_priv_to_result_priv(opt, result);
    return;
  }
  trace2_region_leave("merge", "collect_merge_info", opt->repo);

  trace2_region_enter("merge", "renames", opt->repo);
  result->clean = detect_and_process_renames(opt);
  trace2_region_leave("merge", "renames", opt->repo);
  if (opt->priv->renames.redo_after_renames == 2) {
    trace2_region_enter("merge", "reset_maps", opt->repo);
    clear_or_reinit_internal_opts(opt->priv, 1);
    trace2_region_leave("merge", "reset_maps", opt->repo);
    goto redo;
  }

  trace2_region_enter("merge", "process_entries", opt->repo);
  if (process_entries(opt, &working_tree_oid) < 0)
    result->clean = -1;
  trace2_region_leave("merge", "process_entries", opt->repo);

  /* Set return values */
  result->path_messages = &opt->priv->conflicts;

  if (result->clean >= 0) {
    if (!opt->mergeability_only) {
      result->tree = repo_parse_tree_indirect(opt->repo,
                &working_tree_oid);
      if (!result->tree)
        die(_("unable to read tree (%s)"),
            oid_to_hex(&working_tree_oid));
    }
    /* existence of conflicted entries implies unclean */
    result->clean &= strmap_empty(&opt->priv->conflicted);
  }
  if (!opt->priv->call_depth || result->clean < 0)
    move_opt_priv_to_result_priv(opt, result);
}

/*
 * Originally from merge_recursive_internal(); somewhat adapted, though.
 */
static void merge_ort_internal(struct merge_options *opt,
             const struct commit_list *_merge_bases,
             struct commit *h1,
             struct commit *h2,
             struct merge_result *result)
{
  struct commit_list *merge_bases = commit_list_copy(_merge_bases);
  struct commit *next;
  struct commit *merged_merge_bases;
  const char *ancestor_name;
  struct strbuf merge_base_abbrev = STRBUF_INIT;

  if (!merge_bases) {
    if (repo_get_merge_bases(opt->repo, h1, h2,
           &merge_bases) < 0) {
      result->clean = -1;
      goto out;
    }
    /* See merge-ort.h:merge_incore_recursive() declaration NOTE */
    merge_bases = commit_list_reverse(merge_bases);
  }

  merged_merge_bases = pop_commit(&merge_bases);
  if (!merged_merge_bases) {
    /* if there is no common ancestor, use an empty tree */
    struct tree *tree;

    tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
    merged_merge_bases = make_virtual_commit(opt->repo, tree,
               "ancestor");
    ancestor_name = "empty tree";
  } else if (merge_bases) {
    ancestor_name = "merged common ancestors";
  } else if (opt->ancestor) {
    ancestor_name = opt->ancestor;
  } else {
    strbuf_add_unique_abbrev(&merge_base_abbrev,
           &merged_merge_bases->object.oid,
           DEFAULT_ABBREV);
    ancestor_name = merge_base_abbrev.buf;
  }

  for (next = pop_commit(&merge_bases); next;
       next = pop_commit(&merge_bases)) {
    const char *saved_b1, *saved_b2;
    struct commit *prev = merged_merge_bases;

    opt->priv->call_depth++;
    /*
     * When the merge fails, the result contains files
     * with conflict markers. The cleanness flag is
     * ignored (unless indicating an error), it was never
     * actually used, as result of merge_trees has always
     * overwritten it: the committed "conflicts" were
     * already resolved.
     */
    saved_b1 = opt->branch1;
    saved_b2 = opt->branch2;
    opt->branch1 = "Temporary merge branch 1";
    opt->branch2 = "Temporary merge branch 2";
    merge_ort_internal(opt, NULL, prev, next, result);
    if (result->clean < 0)
      goto out;
    opt->branch1 = saved_b1;
    opt->branch2 = saved_b2;
    opt->priv->call_depth--;

    merged_merge_bases = make_virtual_commit(opt->repo,
               result->tree,
               "merged tree");
    commit_list_insert(prev, &merged_merge_bases->parents);
    commit_list_insert(next, &merged_merge_bases->parents->next);

    clear_or_reinit_internal_opts(opt->priv, 1);
  }

  opt->ancestor = ancestor_name;
  merge_ort_nonrecursive_internal(opt,
          repo_get_commit_tree(opt->repo,
                   merged_merge_bases),
          repo_get_commit_tree(opt->repo, h1),
          repo_get_commit_tree(opt->repo, h2),
          result);
  strbuf_release(&merge_base_abbrev);
  opt->ancestor = NULL;  /* avoid accidental re-use of opt->ancestor */

out:
  commit_list_free(merge_bases);
}

void merge_incore_nonrecursive(struct merge_options *opt,
             struct tree *merge_base,
             struct tree *side1,
             struct tree *side2,
             struct merge_result *result)
{
  trace2_region_enter("merge", "incore_nonrecursive", opt->repo);

  trace2_region_enter("merge", "merge_start", opt->repo);
  assert(opt->ancestor != NULL);
  merge_check_renames_reusable(opt, result, merge_base, side1, side2);
  merge_start(opt, result);
  /*
   * Record the trees used in this merge, so if there's a next merge in
   * a cherry-pick or rebase sequence it might be able to take advantage
   * of the cached_pairs in that next merge.
   */
  opt->priv->renames.merge_trees[0] = merge_base;
  opt->priv->renames.merge_trees[1] = side1;
  opt->priv->renames.merge_trees[2] = side2;
  trace2_region_leave("merge", "merge_start", opt->repo);

  merge_ort_nonrecursive_internal(opt, merge_base, side1, side2, result);
  trace2_region_leave("merge", "incore_nonrecursive", opt->repo);
}

void merge_incore_recursive(struct merge_options *opt,
          const struct commit_list *merge_bases,
          struct commit *side1,
          struct commit *side2,
          struct merge_result *result)
{
  trace2_region_enter("merge", "incore_recursive", opt->repo);

  /*
   * We set the ancestor label based on the merge_bases...but we
   * allow one exception through so that builtin/am can override
   * with its constructed fake ancestor.
   */
  assert(opt->ancestor == NULL ||
         (merge_bases && !merge_bases->next));

  trace2_region_enter("merge", "merge_start", opt->repo);
  merge_start(opt, result);
  trace2_region_leave("merge", "merge_start", opt->repo);

  merge_ort_internal(opt, merge_bases, side1, side2, result);
  trace2_region_leave("merge", "incore_recursive", opt->repo);
}

static void merge_recursive_config(struct merge_options *opt, int ui)
{
  char *value = NULL;
  int renormalize = 0;
  repo_config_get_int(opt->repo, "merge.verbosity", &opt->verbosity);
  repo_config_get_int(opt->repo, "diff.renamelimit", &opt->rename_limit);
  repo_config_get_int(opt->repo, "merge.renamelimit", &opt->rename_limit);
  repo_config_get_bool(opt->repo, "merge.renormalize", &renormalize);
  opt->renormalize = renormalize;
  if (!repo_config_get_string(opt->repo, "diff.renames", &value)) {
    opt->detect_renames = git_config_rename("diff.renames", value);
    free(value);
  }
  if (!repo_config_get_string(opt->repo, "merge.renames", &value)) {
    opt->detect_renames = git_config_rename("merge.renames", value);
    free(value);
  }
  if (!repo_config_get_string(opt->repo, "merge.directoryrenames", &value)) {
    int boolval = git_parse_maybe_bool(value);
    if (0 <= boolval) {
      opt->detect_directory_renames = boolval ?
        MERGE_DIRECTORY_RENAMES_TRUE :
        MERGE_DIRECTORY_RENAMES_NONE;
    } else if (!strcasecmp(value, "conflict")) {
      opt->detect_directory_renames =
        MERGE_DIRECTORY_RENAMES_CONFLICT;
    } /* avoid erroring on values from future versions of git */
    free(value);
  }
  if (ui) {
    if (!repo_config_get_string(opt->repo, "diff.algorithm", &value)) {
      long diff_algorithm = parse_algorithm_value(value);
      if (diff_algorithm < 0)
        die(_("unknown value for config '%s': %s"), "diff.algorithm", value);
      opt->xdl_opts = (opt->xdl_opts & ~XDF_DIFF_ALGORITHM_MASK) | diff_algorithm;
      free(value);
    }
  }
  repo_config(opt->repo, git_xmerge_config, NULL);
}

static void init_merge_options(struct merge_options *opt,
      struct repository *repo, int ui)
{
  const char *merge_verbosity;
  memset(opt, 0, sizeof(struct merge_options));

  opt->repo = repo;

  opt->detect_renames = -1;
  opt->detect_directory_renames = MERGE_DIRECTORY_RENAMES_CONFLICT;
  opt->rename_limit = -1;

  opt->verbosity = 2;
  opt->buffer_output = 1;
  strbuf_init(&opt->obuf, 0);

  opt->renormalize = 0;

  opt->conflict_style = -1;
  opt->xdl_opts = DIFF_WITH_ALG(opt, HISTOGRAM_DIFF);

  merge_recursive_config(opt, ui);
  merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
  if (merge_verbosity)
    opt->verbosity = strtol(merge_verbosity, NULL, 10);
  if (opt->verbosity >= 5)
    opt->buffer_output = 0;
}

void init_ui_merge_options(struct merge_options *opt,
      struct repository *repo)
{
  init_merge_options(opt, repo, 1);
}

void init_basic_merge_options(struct merge_options *opt,
      struct repository *repo)
{
  init_merge_options(opt, repo, 0);
}

/*
 * For now, members of merge_options do not need deep copying, but
 * it may change in the future, in which case we would need to update
 * this, and also make a matching change to clear_merge_options() to
 * release the resources held by a copied instance.
 */
void copy_merge_options(struct merge_options *dst, struct merge_options *src)
{
  *dst = *src;
}

void clear_merge_options(struct merge_options *opt UNUSED)
{
  ; /* no-op as our copy is shallow right now */
}

int parse_merge_opt(struct merge_options *opt, const char *s)
{
  const char *arg;

  if (!s || !*s)
    return -1;
  if (!strcmp(s, "ours"))
    opt->recursive_variant = MERGE_VARIANT_OURS;
  else if (!strcmp(s, "theirs"))
    opt->recursive_variant = MERGE_VARIANT_THEIRS;
  else if (!strcmp(s, "subtree"))
    opt->subtree_shift = "";
  else if (skip_prefix(s, "subtree=", &arg))
    opt->subtree_shift = arg;
  else if (!strcmp(s, "patience"))
    opt->xdl_opts = DIFF_WITH_ALG(opt, PATIENCE_DIFF);
  else if (!strcmp(s, "histogram"))
    opt->xdl_opts = DIFF_WITH_ALG(opt, HISTOGRAM_DIFF);
  else if (skip_prefix(s, "diff-algorithm=", &arg)) {
    long value = parse_algorithm_value(arg);
    if (value < 0)
      return -1;
    /* clear out previous settings */
    opt->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
    opt->xdl_opts |= value;
  }
  else if (!strcmp(s, "ignore-space-change"))
    DIFF_XDL_SET(opt, IGNORE_WHITESPACE_CHANGE);
  else if (!strcmp(s, "ignore-all-space"))
    DIFF_XDL_SET(opt, IGNORE_WHITESPACE);
  else if (!strcmp(s, "ignore-space-at-eol"))
    DIFF_XDL_SET(opt, IGNORE_WHITESPACE_AT_EOL);
  else if (!strcmp(s, "ignore-cr-at-eol"))
    DIFF_XDL_SET(opt, IGNORE_CR_AT_EOL);
  else if (!strcmp(s, "renormalize"))
    opt->renormalize = 1;
  else if (!strcmp(s, "no-renormalize"))
    opt->renormalize = 0;
  else if (!strcmp(s, "no-renames"))
    opt->detect_renames = 0;
  else if (!strcmp(s, "find-renames")) {
    opt->detect_renames = 1;
    opt->rename_score = 0;
  }
  else if (skip_prefix(s, "find-renames=", &arg) ||
     skip_prefix(s, "rename-threshold=", &arg)) {
    if ((opt->rename_score = parse_rename_score(&arg)) == -1 || *arg != 0)
      return -1;
    opt->detect_renames = 1;
  }
  /*
   * Please update $__git_merge_strategy_options in
   * git-completion.bash when you add new options
   */
  else
    return -1;
  return 0;
}

Coverage Report

Created: 2026-05-10 06:11