/src/git/merge-recursive.c

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/*
 * Recursive Merge algorithm stolen from git-merge-recursive.py by
 * Fredrik Kuivinen.
 * The thieves were Alex Riesen and Johannes Schindelin, in June/July 2006
 */

#define USE_THE_REPOSITORY_VARIABLE

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

#include "alloc.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 "merge-ll.h"
#include "lockfile.h"
#include "match-trees.h"
#include "name-hash.h"
#include "object-file.h"
#include "object-name.h"
#include "object-store-ll.h"
#include "path.h"
#include "repository.h"
#include "revision.h"
#include "sparse-index.h"
#include "string-list.h"
#include "symlinks.h"
#include "tag.h"
#include "tree-walk.h"
#include "unpack-trees.h"
#include "xdiff-interface.h"

struct merge_options_internal {
  int call_depth;
  int needed_rename_limit;
  struct hashmap current_file_dir_set;
  struct string_list df_conflict_file_set;
  struct unpack_trees_options unpack_opts;
  struct index_state orig_index;
};

struct path_hashmap_entry {
  struct hashmap_entry e;
  char path[FLEX_ARRAY];
};

static int path_hashmap_cmp(const void *cmp_data UNUSED,
          const struct hashmap_entry *eptr,
          const struct hashmap_entry *entry_or_key,
          const void *keydata)
{
  const struct path_hashmap_entry *a, *b;
  const char *key = keydata;

  a = container_of(eptr, const struct path_hashmap_entry, e);
  b = container_of(entry_or_key, const struct path_hashmap_entry, e);

  return fspathcmp(a->path, key ? key : b->path);
}

/*
 * For dir_rename_entry, directory names are stored as a full path from the
 * toplevel of the repository and do not include a trailing '/'.  Also:
 *
 *   dir:                original name of directory being renamed
 *   non_unique_new_dir: if true, could not determine new_dir
 *   new_dir:            final name of directory being renamed
 *   possible_new_dirs:  temporary used to help determine new_dir; see comments
 *                       in get_directory_renames() for details
 */
struct dir_rename_entry {
  struct hashmap_entry ent;
  char *dir;
  unsigned non_unique_new_dir:1;
  struct strbuf new_dir;
  struct string_list possible_new_dirs;
};

static struct dir_rename_entry *dir_rename_find_entry(struct hashmap *hashmap,
                  char *dir)
{
  struct dir_rename_entry key;

  if (!dir)
    return NULL;
  hashmap_entry_init(&key.ent, strhash(dir));
  key.dir = dir;
  return hashmap_get_entry(hashmap, &key, ent, NULL);
}

static int dir_rename_cmp(const void *cmp_data UNUSED,
        const struct hashmap_entry *eptr,
        const struct hashmap_entry *entry_or_key,
        const void *keydata UNUSED)
{
  const struct dir_rename_entry *e1, *e2;

  e1 = container_of(eptr, const struct dir_rename_entry, ent);
  e2 = container_of(entry_or_key, const struct dir_rename_entry, ent);

  return strcmp(e1->dir, e2->dir);
}

static void dir_rename_init(struct hashmap *map)
{
  hashmap_init(map, dir_rename_cmp, NULL, 0);
}

static void dir_rename_entry_init(struct dir_rename_entry *entry,
          char *directory)
{
  hashmap_entry_init(&entry->ent, strhash(directory));
  entry->dir = directory;
  entry->non_unique_new_dir = 0;
  strbuf_init(&entry->new_dir, 0);
  string_list_init_nodup(&entry->possible_new_dirs);
}

struct collision_entry {
  struct hashmap_entry ent;
  char *target_file;
  struct string_list source_files;
  unsigned reported_already:1;
};

static struct collision_entry *collision_find_entry(struct hashmap *hashmap,
                char *target_file)
{
  struct collision_entry key;

  hashmap_entry_init(&key.ent, strhash(target_file));
  key.target_file = target_file;
  return hashmap_get_entry(hashmap, &key, ent, NULL);
}

static int collision_cmp(const void *cmp_data UNUSED,
       const struct hashmap_entry *eptr,
       const struct hashmap_entry *entry_or_key,
       const void *keydata UNUSED)
{
  const struct collision_entry *e1, *e2;

  e1 = container_of(eptr, const struct collision_entry, ent);
  e2 = container_of(entry_or_key, const struct collision_entry, ent);

  return strcmp(e1->target_file, e2->target_file);
}

static void collision_init(struct hashmap *map)
{
  hashmap_init(map, collision_cmp, NULL, 0);
}

static void flush_output(struct merge_options *opt)
{
  if (opt->buffer_output < 2 && opt->obuf.len) {
    fputs(opt->obuf.buf, stdout);
    strbuf_reset(&opt->obuf);
  }
}

__attribute__((format (printf, 2, 3)))
static int err(struct merge_options *opt, const char *err, ...)
{
  va_list params;

  if (opt->buffer_output < 2)
    flush_output(opt);
  else {
    strbuf_complete(&opt->obuf, '\n');
    strbuf_addstr(&opt->obuf, "error: ");
  }
  va_start(params, err);
  strbuf_vaddf(&opt->obuf, err, params);
  va_end(params);
  if (opt->buffer_output > 1)
    strbuf_addch(&opt->obuf, '\n');
  else {
    error("%s", opt->obuf.buf);
    strbuf_reset(&opt->obuf);
  }

  return -1;
}

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;
}

static 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;
}

enum rename_type {
  RENAME_NORMAL = 0,
  RENAME_VIA_DIR,
  RENAME_ADD,
  RENAME_DELETE,
  RENAME_ONE_FILE_TO_ONE,
  RENAME_ONE_FILE_TO_TWO,
  RENAME_TWO_FILES_TO_ONE
};

/*
 * Since we want to write the index eventually, we cannot reuse the index
 * for these (temporary) data.
 */
struct stage_data {
  struct diff_filespec stages[4]; /* mostly for oid & mode; maybe path */
  struct rename_conflict_info *rename_conflict_info;
  unsigned processed:1,
     rename_conflict_info_owned:1;
};

struct rename {
  unsigned processed:1;
  struct diff_filepair *pair;
  const char *branch; /* branch that the rename occurred on */
  /*
   * If directory rename detection affected this rename, what was its
   * original type ('A' or 'R') and it's original destination before
   * the directory rename (otherwise, '\0' and NULL for these two vars).
   */
  char dir_rename_original_type;
  char *dir_rename_original_dest;
  /*
   * Purpose of src_entry and dst_entry:
   *
   * If 'before' is renamed to 'after' then src_entry will contain
   * the versions of 'before' from the merge_base, HEAD, and MERGE in
   * stages 1, 2, and 3; dst_entry will contain the respective
   * versions of 'after' in corresponding locations.  Thus, we have a
   * total of six modes and oids, though some will be null.  (Stage 0
   * is ignored; we're interested in handling conflicts.)
   *
   * Since we don't turn on break-rewrites by default, neither
   * src_entry nor dst_entry can have all three of their stages have
   * non-null oids, meaning at most four of the six will be non-null.
   * Also, since this is a rename, both src_entry and dst_entry will
   * have at least one non-null oid, meaning at least two will be
   * non-null.  Of the six oids, a typical rename will have three be
   * non-null.  Only two implies a rename/delete, and four implies a
   * rename/add.
   */
  struct stage_data *src_entry;
  struct stage_data *dst_entry;
};

struct rename_conflict_info {
  enum rename_type rename_type;
  struct rename *ren1;
  struct rename *ren2;
};

static inline void setup_rename_conflict_info(enum rename_type rename_type,
                struct merge_options *opt,
                struct rename *ren1,
                struct rename *ren2)
{
  struct rename_conflict_info *ci;

  /*
   * When we have two renames involved, it's easiest to get the
   * correct things into stage 2 and 3, and to make sure that the
   * content merge puts HEAD before the other branch if we just
   * ensure that branch1 == opt->branch1.  So, simply flip arguments
   * around if we don't have that.
   */
  if (ren2 && ren1->branch != opt->branch1) {
    setup_rename_conflict_info(rename_type, opt, ren2, ren1);
    return;
  }

  CALLOC_ARRAY(ci, 1);
  ci->rename_type = rename_type;
  ci->ren1 = ren1;
  ci->ren2 = ren2;

  ci->ren1->dst_entry->processed = 0;
  ci->ren1->dst_entry->rename_conflict_info = ci;
  ci->ren1->dst_entry->rename_conflict_info_owned = 1;
  if (ren2) {
    ci->ren2->dst_entry->rename_conflict_info = ci;
  }
}

static int show(struct merge_options *opt, int v)
{
  return (!opt->priv->call_depth && opt->verbosity >= v) ||
    opt->verbosity >= 5;
}

__attribute__((format (printf, 3, 4)))
static void output(struct merge_options *opt, int v, const char *fmt, ...)
{
  va_list ap;

  if (!show(opt, v))
    return;

  strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);

  va_start(ap, fmt);
  strbuf_vaddf(&opt->obuf, fmt, ap);
  va_end(ap);

  strbuf_addch(&opt->obuf, '\n');
  if (!opt->buffer_output)
    flush_output(opt);
}

static void repo_output_commit_title(struct merge_options *opt,
             struct repository *repo,
             struct commit *commit)
{
  struct merge_remote_desc *desc;

  strbuf_addchars(&opt->obuf, ' ', opt->priv->call_depth * 2);
  desc = merge_remote_util(commit);
  if (desc)
    strbuf_addf(&opt->obuf, "virtual %s\n", desc->name);
  else {
    strbuf_repo_add_unique_abbrev(&opt->obuf, repo,
                &commit->object.oid,
                DEFAULT_ABBREV);
    strbuf_addch(&opt->obuf, ' ');
    if (repo_parse_commit(repo, commit) != 0)
      strbuf_addstr(&opt->obuf, _("(bad commit)\n"));
    else {
      const char *title;
      const char *msg = repo_get_commit_buffer(repo, commit, NULL);
      int len = find_commit_subject(msg, &title);
      if (len)
        strbuf_addf(&opt->obuf, "%.*s\n", len, title);
      repo_unuse_commit_buffer(repo, commit, msg);
    }
  }
  flush_output(opt);
}

static void output_commit_title(struct merge_options *opt, struct commit *commit)
{
  repo_output_commit_title(opt, the_repository, commit);
}

static int add_cacheinfo(struct merge_options *opt,
       const struct diff_filespec *blob,
       const char *path, int stage, int refresh, int options)
{
  struct index_state *istate = opt->repo->index;
  struct cache_entry *ce;
  int ret;

  ce = make_cache_entry(istate, blob->mode, &blob->oid, path, stage, 0);
  if (!ce)
    return err(opt, _("add_cacheinfo failed for path '%s'; merge aborting."), path);

  ret = add_index_entry(istate, ce, options);
  if (refresh) {
    struct cache_entry *nce;

    nce = refresh_cache_entry(istate, ce,
            CE_MATCH_REFRESH | CE_MATCH_IGNORE_MISSING);
    if (!nce)
      return err(opt, _("add_cacheinfo failed to refresh for path '%s'; merge aborting."), path);
    if (nce != ce)
      ret = add_index_entry(istate, nce, options);
  }
  return ret;
}

static inline int merge_detect_rename(struct merge_options *opt)
{
  return (opt->detect_renames >= 0) ? opt->detect_renames : 1;
}

static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
{
  if (parse_tree(tree) < 0)
    exit(128);
  init_tree_desc(desc, &tree->object.oid, tree->buffer, tree->size);
}

static int unpack_trees_start(struct merge_options *opt,
            struct tree *common,
            struct tree *head,
            struct tree *merge)
{
  int rc;
  struct tree_desc t[3];
  struct index_state tmp_index = INDEX_STATE_INIT(opt->repo);

  memset(&opt->priv->unpack_opts, 0, sizeof(opt->priv->unpack_opts));
  if (opt->priv->call_depth)
    opt->priv->unpack_opts.index_only = 1;
  else {
    opt->priv->unpack_opts.update = 1;
    /* FIXME: should only do this if !overwrite_ignore */
    opt->priv->unpack_opts.preserve_ignored = 0;
  }
  opt->priv->unpack_opts.merge = 1;
  opt->priv->unpack_opts.head_idx = 2;
  opt->priv->unpack_opts.fn = threeway_merge;
  opt->priv->unpack_opts.src_index = opt->repo->index;
  opt->priv->unpack_opts.dst_index = &tmp_index;
  opt->priv->unpack_opts.aggressive = !merge_detect_rename(opt);
  setup_unpack_trees_porcelain(&opt->priv->unpack_opts, "merge");

  init_tree_desc_from_tree(t+0, common);
  init_tree_desc_from_tree(t+1, head);
  init_tree_desc_from_tree(t+2, merge);

  rc = unpack_trees(3, t, &opt->priv->unpack_opts);
  cache_tree_free(&opt->repo->index->cache_tree);

  /*
   * Update opt->repo->index to match the new results, AFTER saving a
   * copy in opt->priv->orig_index.  Update src_index to point to the
   * saved copy.  (verify_uptodate() checks src_index, and the original
   * index is the one that had the necessary modification timestamps.)
   */
  opt->priv->orig_index = *opt->repo->index;
  *opt->repo->index = tmp_index;
  opt->priv->unpack_opts.src_index = &opt->priv->orig_index;

  return rc;
}

static void unpack_trees_finish(struct merge_options *opt)
{
  discard_index(&opt->priv->orig_index);
  clear_unpack_trees_porcelain(&opt->priv->unpack_opts);
}

static int save_files_dirs(const struct object_id *oid UNUSED,
         struct strbuf *base, const char *path,
         unsigned int mode, void *context)
{
  struct path_hashmap_entry *entry;
  int baselen = base->len;
  struct merge_options *opt = context;

  strbuf_addstr(base, path);

  FLEX_ALLOC_MEM(entry, path, base->buf, base->len);
  hashmap_entry_init(&entry->e, fspathhash(entry->path));
  hashmap_add(&opt->priv->current_file_dir_set, &entry->e);

  strbuf_setlen(base, baselen);
  return (S_ISDIR(mode) ? READ_TREE_RECURSIVE : 0);
}

static void get_files_dirs(struct merge_options *opt, struct tree *tree)
{
  struct pathspec match_all;
  memset(&match_all, 0, sizeof(match_all));
  read_tree(opt->repo, tree,
      &match_all, save_files_dirs, opt);
}

static int get_tree_entry_if_blob(struct repository *r,
          const struct object_id *tree,
          const char *path,
          struct diff_filespec *dfs)
{
  int ret;

  ret = get_tree_entry(r, tree, path, &dfs->oid, &dfs->mode);
  if (S_ISDIR(dfs->mode)) {
    oidcpy(&dfs->oid, null_oid());
    dfs->mode = 0;
  }
  return ret;
}

/*
 * Returns an index_entry instance which doesn't have to correspond to
 * a real cache entry in Git's index.
 */
static struct stage_data *insert_stage_data(struct repository *r,
    const char *path,
    struct tree *o, struct tree *a, struct tree *b,
    struct string_list *entries)
{
  struct string_list_item *item;
  struct stage_data *e = xcalloc(1, sizeof(struct stage_data));
  get_tree_entry_if_blob(r, &o->object.oid, path, &e->stages[1]);
  get_tree_entry_if_blob(r, &a->object.oid, path, &e->stages[2]);
  get_tree_entry_if_blob(r, &b->object.oid, path, &e->stages[3]);
  item = string_list_insert(entries, path);
  item->util = e;
  return e;
}

/*
 * Create a dictionary mapping file names to stage_data objects. The
 * dictionary contains one entry for every path with a non-zero stage entry.
 */
static struct string_list *get_unmerged(struct index_state *istate)
{
  struct string_list *unmerged = xmalloc(sizeof(struct string_list));
  int i;

  string_list_init_dup(unmerged);

  /* TODO: audit for interaction with sparse-index. */
  ensure_full_index(istate);
  for (i = 0; i < istate->cache_nr; i++) {
    struct string_list_item *item;
    struct stage_data *e;
    const struct cache_entry *ce = istate->cache[i];
    if (!ce_stage(ce))
      continue;

    item = string_list_lookup(unmerged, ce->name);
    if (!item) {
      item = string_list_insert(unmerged, ce->name);
      item->util = xcalloc(1, sizeof(struct stage_data));
    }
    e = item->util;
    e->stages[ce_stage(ce)].mode = ce->ce_mode;
    oidcpy(&e->stages[ce_stage(ce)].oid, &ce->oid);
  }

  return unmerged;
}

static int string_list_df_name_compare(const char *one, const char *two)
{
  int onelen = strlen(one);
  int twolen = strlen(two);
  /*
   * Here we only care that entries for D/F conflicts are
   * adjacent, in particular with the file of the D/F conflict
   * appearing before files below the corresponding directory.
   * The order of the rest of the list is irrelevant for us.
   *
   * To achieve this, we sort with df_name_compare and provide
   * the mode S_IFDIR so that D/F conflicts will sort correctly.
   * We use the mode S_IFDIR for everything else for simplicity,
   * since in other cases any changes in their order due to
   * sorting cause no problems for us.
   */
  int cmp = df_name_compare(one, onelen, S_IFDIR,
          two, twolen, S_IFDIR);
  /*
   * Now that 'foo' and 'foo/bar' compare equal, we have to make sure
   * that 'foo' comes before 'foo/bar'.
   */
  if (cmp)
    return cmp;
  return onelen - twolen;
}

static void record_df_conflict_files(struct merge_options *opt,
             struct string_list *entries)
{
  /* If there is a D/F conflict and the file for such a conflict
   * currently exists in the working tree, we want to allow it to be
   * removed to make room for the corresponding directory if needed.
   * The files underneath the directories of such D/F conflicts will
   * be processed before the corresponding file involved in the D/F
   * conflict.  If the D/F directory ends up being removed by the
   * merge, then we won't have to touch the D/F file.  If the D/F
   * directory needs to be written to the working copy, then the D/F
   * file will simply be removed (in make_room_for_path()) to make
   * room for the necessary paths.  Note that if both the directory
   * and the file need to be present, then the D/F file will be
   * reinstated with a new unique name at the time it is processed.
   */
  struct string_list df_sorted_entries = STRING_LIST_INIT_NODUP;
  const char *last_file = NULL;
  int last_len = 0;
  int i;

  /*
   * If we're merging merge-bases, we don't want to bother with
   * any working directory changes.
   */
  if (opt->priv->call_depth)
    return;

  /* Ensure D/F conflicts are adjacent in the entries list. */
  for (i = 0; i < entries->nr; i++) {
    struct string_list_item *next = &entries->items[i];
    string_list_append(&df_sorted_entries, next->string)->util =
           next->util;
  }
  df_sorted_entries.cmp = string_list_df_name_compare;
  string_list_sort(&df_sorted_entries);

  string_list_clear(&opt->priv->df_conflict_file_set, 1);
  for (i = 0; i < df_sorted_entries.nr; i++) {
    const char *path = df_sorted_entries.items[i].string;
    int len = strlen(path);
    struct stage_data *e = df_sorted_entries.items[i].util;

    /*
     * Check if last_file & path correspond to a D/F conflict;
     * i.e. whether path is last_file+'/'+<something>.
     * If so, record that it's okay to remove last_file to make
     * room for path and friends if needed.
     */
    if (last_file &&
        len > last_len &&
        memcmp(path, last_file, last_len) == 0 &&
        path[last_len] == '/') {
      string_list_insert(&opt->priv->df_conflict_file_set, last_file);
    }

    /*
     * Determine whether path could exist as a file in the
     * working directory as a possible D/F conflict.  This
     * will only occur when it exists in stage 2 as a
     * file.
     */
    if (S_ISREG(e->stages[2].mode) || S_ISLNK(e->stages[2].mode)) {
      last_file = path;
      last_len = len;
    } else {
      last_file = NULL;
    }
  }
  string_list_clear(&df_sorted_entries, 0);
}

static int update_stages(struct merge_options *opt, const char *path,
       const struct diff_filespec *o,
       const struct diff_filespec *a,
       const struct diff_filespec *b)
{

  /*
   * NOTE: It is usually a bad idea to call update_stages on a path
   * before calling update_file on that same path, since it can
   * sometimes lead to spurious "refusing to lose untracked file..."
   * messages from update_file (via make_room_for path via
   * would_lose_untracked).  Instead, reverse the order of the calls
   * (executing update_file first and then update_stages).
   */
  int clear = 1;
  int options = ADD_CACHE_OK_TO_ADD | ADD_CACHE_SKIP_DFCHECK;
  if (clear)
    if (remove_file_from_index(opt->repo->index, path))
      return -1;
  if (o)
    if (add_cacheinfo(opt, o, path, 1, 0, options))
      return -1;
  if (a)
    if (add_cacheinfo(opt, a, path, 2, 0, options))
      return -1;
  if (b)
    if (add_cacheinfo(opt, b, path, 3, 0, options))
      return -1;
  return 0;
}

static void update_entry(struct stage_data *entry,
       struct diff_filespec *o,
       struct diff_filespec *a,
       struct diff_filespec *b)
{
  entry->processed = 0;
  entry->stages[1].mode = o->mode;
  entry->stages[2].mode = a->mode;
  entry->stages[3].mode = b->mode;
  oidcpy(&entry->stages[1].oid, &o->oid);
  oidcpy(&entry->stages[2].oid, &a->oid);
  oidcpy(&entry->stages[3].oid, &b->oid);
}

static int remove_file(struct merge_options *opt, int clean,
           const char *path, int no_wd)
{
  int update_cache = opt->priv->call_depth || clean;
  int update_working_directory = !opt->priv->call_depth && !no_wd;

  if (update_cache) {
    if (remove_file_from_index(opt->repo->index, path))
      return -1;
  }
  if (update_working_directory) {
    if (ignore_case) {
      struct cache_entry *ce;
      ce = index_file_exists(opt->repo->index, path, strlen(path),
                 ignore_case);
      if (ce && ce_stage(ce) == 0 && strcmp(path, ce->name))
        return 0;
    }
    if (remove_path(path))
      return -1;
  }
  return 0;
}

/* 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)
{
  struct path_hashmap_entry *entry;
  struct strbuf newpath = STRBUF_INIT;
  int suffix = 0;
  size_t base_len;

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

  base_len = newpath.len;
  while (hashmap_get_from_hash(&opt->priv->current_file_dir_set,
             fspathhash(newpath.buf), newpath.buf) ||
         (!opt->priv->call_depth && file_exists(newpath.buf))) {
    strbuf_setlen(&newpath, base_len);
    strbuf_addf(&newpath, "_%d", suffix++);
  }

  FLEX_ALLOC_MEM(entry, path, newpath.buf, newpath.len);
  hashmap_entry_init(&entry->e, fspathhash(entry->path));
  hashmap_add(&opt->priv->current_file_dir_set, &entry->e);
  return strbuf_detach(&newpath, NULL);
}

/**
 * Check whether a directory in the index is in the way of an incoming
 * file.  Return 1 if so.  If check_working_copy is non-zero, also
 * check the working directory.  If empty_ok is non-zero, also return
 * 0 in the case where the working-tree dir exists but is empty.
 */
static int dir_in_way(struct index_state *istate, const char *path,
          int check_working_copy, int empty_ok)
{
  int pos;
  struct strbuf dirpath = STRBUF_INIT;
  struct stat st;

  strbuf_addstr(&dirpath, path);
  strbuf_addch(&dirpath, '/');

  pos = index_name_pos(istate, dirpath.buf, dirpath.len);

  if (pos < 0)
    pos = -1 - pos;
  if (pos < istate->cache_nr &&
      !strncmp(dirpath.buf, istate->cache[pos]->name, dirpath.len)) {
    strbuf_release(&dirpath);
    return 1;
  }

  strbuf_release(&dirpath);
  return check_working_copy && !lstat(path, &st) && S_ISDIR(st.st_mode) &&
    !(empty_ok && is_empty_dir(path)) &&
    !has_symlink_leading_path(path, strlen(path));
}

/*
 * Returns whether path was tracked in the index before the merge started,
 * and its oid and mode match the specified values
 */
static int was_tracked_and_matches(struct merge_options *opt, const char *path,
           const struct diff_filespec *blob)
{
  int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
  struct cache_entry *ce;

  if (0 > pos)
    /* we were not tracking this path before the merge */
    return 0;

  /* See if the file we were tracking before matches */
  ce = opt->priv->orig_index.cache[pos];
  return (oideq(&ce->oid, &blob->oid) && ce->ce_mode == blob->mode);
}

/*
 * Returns whether path was tracked in the index before the merge started
 */
static int was_tracked(struct merge_options *opt, const char *path)
{
  int pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));

  if (0 <= pos)
    /* we were tracking this path before the merge */
    return 1;

  return 0;
}

static int would_lose_untracked(struct merge_options *opt, const char *path)
{
  struct index_state *istate = opt->repo->index;

  /*
   * This may look like it can be simplified to:
   *   return !was_tracked(opt, path) && file_exists(path)
   * but it can't.  This function needs to know whether path was in
   * the working tree due to EITHER having been tracked in the index
   * before the merge OR having been put into the working copy and
   * index by unpack_trees().  Due to that either-or requirement, we
   * check the current index instead of the original one.
   *
   * Note that we do not need to worry about merge-recursive itself
   * updating the index after unpack_trees() and before calling this
   * function, because we strictly require all code paths in
   * merge-recursive to update the working tree first and the index
   * second.  Doing otherwise would break
   * update_file()/would_lose_untracked(); see every comment in this
   * file which mentions "update_stages".
   */
  int pos = index_name_pos(istate, path, strlen(path));

  if (pos < 0)
    pos = -1 - pos;
  while (pos < istate->cache_nr &&
         !strcmp(path, istate->cache[pos]->name)) {
    /*
     * If stage #0, it is definitely tracked.
     * If it has stage #2 then it was tracked
     * before this merge started.  All other
     * cases the path was not tracked.
     */
    switch (ce_stage(istate->cache[pos])) {
    case 0:
    case 2:
      return 0;
    }
    pos++;
  }
  return file_exists(path);
}

static int was_dirty(struct merge_options *opt, const char *path)
{
  struct cache_entry *ce;
  int dirty = 1;

  if (opt->priv->call_depth || !was_tracked(opt, path))
    return !dirty;

  ce = index_file_exists(opt->priv->unpack_opts.src_index,
             path, strlen(path), ignore_case);
  dirty = verify_uptodate(ce, &opt->priv->unpack_opts) != 0;
  return dirty;
}

static int make_room_for_path(struct merge_options *opt, const char *path)
{
  int status, i;
  const char *msg = _("failed to create path '%s'%s");

  /* Unlink any D/F conflict files that are in the way */
  for (i = 0; i < opt->priv->df_conflict_file_set.nr; i++) {
    const char *df_path = opt->priv->df_conflict_file_set.items[i].string;
    size_t pathlen = strlen(path);
    size_t df_pathlen = strlen(df_path);
    if (df_pathlen < pathlen &&
        path[df_pathlen] == '/' &&
        strncmp(path, df_path, df_pathlen) == 0) {
      output(opt, 3,
             _("Removing %s to make room for subdirectory\n"),
             df_path);
      unlink(df_path);
      unsorted_string_list_delete_item(&opt->priv->df_conflict_file_set,
               i, 0);
      break;
    }
  }

  /* Make sure leading directories are created */
  status = safe_create_leading_directories_const(path);
  if (status) {
    if (status == SCLD_EXISTS)
      /* something else exists */
      return err(opt, msg, path, _(": perhaps a D/F conflict?"));
    return err(opt, msg, path, "");
  }

  /*
   * Do not unlink a file in the work tree if we are not
   * tracking it.
   */
  if (would_lose_untracked(opt, path))
    return err(opt, _("refusing to lose untracked file at '%s'"),
         path);

  /* Successful unlink is good.. */
  if (!unlink(path))
    return 0;
  /* .. and so is no existing file */
  if (errno == ENOENT)
    return 0;
  /* .. but not some other error (who really cares what?) */
  return err(opt, msg, path, _(": perhaps a D/F conflict?"));
}

static int update_file_flags(struct merge_options *opt,
           const struct diff_filespec *contents,
           const char *path,
           int update_cache,
           int update_wd)
{
  int ret = 0;

  if (opt->priv->call_depth)
    update_wd = 0;

  if (update_wd) {
    enum object_type type;
    void *buf;
    unsigned long size;

    if (S_ISGITLINK(contents->mode)) {
      /*
       * We may later decide to recursively descend into
       * the submodule directory and update its index
       * and/or work tree, but we do not do that now.
       */
      update_wd = 0;
      goto update_index;
    }

    buf = repo_read_object_file(the_repository, &contents->oid,
              &type, &size);
    if (!buf) {
      ret = err(opt, _("cannot read object %s '%s'"),
          oid_to_hex(&contents->oid), path);
      goto free_buf;
    }
    if (type != OBJ_BLOB) {
      ret = err(opt, _("blob expected for %s '%s'"),
          oid_to_hex(&contents->oid), path);
      goto free_buf;
    }
    if (S_ISREG(contents->mode)) {
      struct strbuf strbuf = STRBUF_INIT;
      if (convert_to_working_tree(opt->repo->index,
                path, buf, size, &strbuf, NULL)) {
        free(buf);
        size = strbuf.len;
        buf = strbuf_detach(&strbuf, NULL);
      }
    }

    if (make_room_for_path(opt, path) < 0) {
      update_wd = 0;
      goto free_buf;
    }
    if (S_ISREG(contents->mode) ||
        (!has_symlinks && S_ISLNK(contents->mode))) {
      int fd;
      int mode = (contents->mode & 0100 ? 0777 : 0666);

      fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, mode);
      if (fd < 0) {
        ret = err(opt, _("failed to open '%s': %s"),
            path, strerror(errno));
        goto free_buf;
      }
      write_in_full(fd, buf, size);
      close(fd);
    } else if (S_ISLNK(contents->mode)) {
      char *lnk = xmemdupz(buf, size);
      safe_create_leading_directories_const(path);
      unlink(path);
      if (symlink(lnk, path))
        ret = err(opt, _("failed to symlink '%s': %s"),
            path, strerror(errno));
      free(lnk);
    } else
      ret = err(opt,
          _("do not know what to do with %06o %s '%s'"),
          contents->mode, oid_to_hex(&contents->oid), path);
  free_buf:
    free(buf);
  }
update_index:
  if (!ret && update_cache) {
    int refresh = (!opt->priv->call_depth &&
             contents->mode != S_IFGITLINK);
    if (add_cacheinfo(opt, contents, path, 0, refresh,
          ADD_CACHE_OK_TO_ADD))
      return -1;
  }
  return ret;
}

static int update_file(struct merge_options *opt,
           int clean,
           const struct diff_filespec *contents,
           const char *path)
{
  return update_file_flags(opt, contents, path,
         opt->priv->call_depth || clean, !opt->priv->call_depth);
}

/* Low level file merging, update and removal */

struct merge_file_info {
  struct diff_filespec blob; /* mostly use oid & mode; sometimes path */
  unsigned clean:1,
     merge:1;
};

static int merge_3way(struct merge_options *opt,
          mmbuffer_t *result_buf,
          const struct diff_filespec *o,
          const struct diff_filespec *a,
          const struct diff_filespec *b,
          const char *branch1,
          const char *branch2,
          const int extra_marker_size)
{
  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;

  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(a->path && b->path && o->path && opt->ancestor);
  if (strcmp(a->path, b->path) || strcmp(a->path, o->path) != 0) {
    base  = mkpathdup("%s:%s", opt->ancestor, o->path);
    name1 = mkpathdup("%s:%s", branch1, a->path);
    name2 = mkpathdup("%s:%s", branch2, b->path);
  } else {
    base  = mkpathdup("%s", opt->ancestor);
    name1 = mkpathdup("%s", branch1);
    name2 = mkpathdup("%s", branch2);
  }

  read_mmblob(&orig, &o->oid);
  read_mmblob(&src1, &a->oid);
  read_mmblob(&src2, &b->oid);

  /*
   * FIXME: Using a->path for normalization rules in ll_merge could be
   * wrong if we renamed from a->path to b->path.  We should use the
   * target path for where the file will be written.
   */
  merge_status = ll_merge(result_buf, a->path, &orig, base,
        &src1, name1, &src2, name2,
        opt->repo->index, &ll_opts);
  if (merge_status == LL_MERGE_BINARY_CONFLICT)
    warning("Cannot merge binary files: %s (%s vs. %s)",
      a->path, name1, name2);

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

static int find_first_merges(struct repository *repo,
           struct object_array *result, const char *path,
           struct commit *a, struct commit *b)
{
  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)
      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 void print_commit(struct repository *repo, struct commit *commit)
{
  struct strbuf sb = STRBUF_INIT;
  struct pretty_print_context ctx = {0};
  ctx.date_mode.type = DATE_NORMAL;
  /* FIXME: Merge this with output_commit_title() */
  assert(!merge_remote_util(commit));
  repo_format_commit_message(repo, commit, " %h: %m %s", &sb, &ctx);
  fprintf(stderr, "%s\n", sb.buf);
  strbuf_release(&sb);
}

static int is_valid(const struct diff_filespec *dfs)
{
  return dfs->mode != 0 && !is_null_oid(&dfs->oid);
}

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

  int i;
  int search = !opt->priv->call_depth;

  /* store a in result in case we fail */
  /* FIXME: This is the WRONG resolution for the recursive case when
   * we need to be careful to avoid accidentally matching either side.
   * Should probably use o instead there, much like we do for merging
   * binaries.
   */
  oidcpy(result, a);

  /* we can not handle deletion conflicts */
  if (is_null_oid(base))
    return 0;
  if (is_null_oid(a))
    return 0;
  if (is_null_oid(b))
    return 0;

  if (repo_submodule_init(&subrepo, opt->repo, path, null_oid())) {
    output(opt, 1, _("Failed to merge submodule %s (not checked out)"), path);
    return 0;
  }

  if (!(commit_base = lookup_commit_reference(&subrepo, base)) ||
      !(commit_a = lookup_commit_reference(&subrepo, a)) ||
      !(commit_b = lookup_commit_reference(&subrepo, b))) {
    output(opt, 1, _("Failed to merge submodule %s (commits not present)"), path);
    goto cleanup;
  }

  /* check whether both changes are forward */
  ret2 = repo_in_merge_bases(&subrepo, commit_base, commit_a);
  if (ret2 < 0) {
    output(opt, 1, _("Failed to merge submodule %s (repository corrupt)"), path);
    ret = -1;
    goto cleanup;
  }
  if (ret2 > 0)
    ret2 = repo_in_merge_bases(&subrepo, commit_base, commit_b);
  if (ret2 < 0) {
    output(opt, 1, _("Failed to merge submodule %s (repository corrupt)"), path);
    ret = -1;
    goto cleanup;
  }
  if (!ret2) {
    output(opt, 1, _("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) {
    output(opt, 1, _("Failed to merge submodule %s (repository corrupt)"), path);
    ret = -1;
    goto cleanup;
  }
  if (ret2) {
    oidcpy(result, b);
    if (show(opt, 3)) {
      output(opt, 3, _("Fast-forwarding submodule %s to the following commit:"), path);
      repo_output_commit_title(opt, &subrepo, commit_b);
    } else if (show(opt, 2))
      output(opt, 2, _("Fast-forwarding submodule %s"), path);
    else
      ; /* no output */

    ret = 1;
    goto cleanup;
  }
  ret2 = repo_in_merge_bases(&subrepo, commit_b, commit_a);
  if (ret2 < 0) {
    output(opt, 1, _("Failed to merge submodule %s (repository corrupt)"), path);
    ret = -1;
    goto cleanup;
  }
  if (ret2) {
    oidcpy(result, a);
    if (show(opt, 3)) {
      output(opt, 3, _("Fast-forwarding submodule %s to the following commit:"), path);
      repo_output_commit_title(opt, &subrepo, commit_a);
    } else if (show(opt, 2))
      output(opt, 2, _("Fast-forwarding submodule %s"), path);
    else
      ; /* no output */

    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, &merges, path,
           commit_a, commit_b);
  switch (parent_count) {
  case -1:
    output(opt, 1,_("Failed to merge submodule %s (repository corrupt)"), path);
    ret = -1;
    break;
  case 0:
    output(opt, 1, _("Failed to merge submodule %s (merge following commits not found)"), path);
    break;

  case 1:
    output(opt, 1, _("Failed to merge submodule %s (not fast-forward)"), path);
    output(opt, 2, _("Found a possible merge resolution for the submodule:\n"));
    print_commit(&subrepo, (struct commit *) merges.objects[0].item);
    output(opt, 2, _(
           "If this is correct simply add it to the index "
           "for example\n"
           "by using:\n\n"
           "  git update-index --cacheinfo 160000 %s \"%s\"\n\n"
           "which will accept this suggestion.\n"),
           oid_to_hex(&merges.objects[0].item->oid), path);
    break;

  default:
    output(opt, 1, _("Failed to merge submodule %s (multiple merges found)"), path);
    for (i = 0; i < merges.nr; i++)
      print_commit(&subrepo, (struct commit *) merges.objects[i].item);
  }

  object_array_clear(&merges);
cleanup:
  repo_clear(&subrepo);
  return ret;
}

static int merge_mode_and_contents(struct merge_options *opt,
           const struct diff_filespec *o,
           const struct diff_filespec *a,
           const struct diff_filespec *b,
           const char *filename,
           const char *branch1,
           const char *branch2,
           const int extra_marker_size,
           struct merge_file_info *result)
{
  if (opt->branch1 != branch1) {
    /*
     * It's weird getting a reverse merge with HEAD on the bottom
     * side of the conflict markers and the other branch on the
     * top.  Fix that.
     */
    return merge_mode_and_contents(opt, o, b, a,
                 filename,
                 branch2, branch1,
                 extra_marker_size, result);
  }

  result->merge = 0;
  result->clean = 1;

  if ((S_IFMT & a->mode) != (S_IFMT & b->mode)) {
    result->clean = 0;
    /*
     * FIXME: This is a bad resolution for recursive case; for
     * the recursive case we want something that is unlikely to
     * accidentally match either side.  Also, while it makes
     * sense to prefer regular files over symlinks, it doesn't
     * make sense to prefer regular files over submodules.
     */
    if (S_ISREG(a->mode)) {
      result->blob.mode = a->mode;
      oidcpy(&result->blob.oid, &a->oid);
    } else {
      result->blob.mode = b->mode;
      oidcpy(&result->blob.oid, &b->oid);
    }
  } else {
    if (!oideq(&a->oid, &o->oid) && !oideq(&b->oid, &o->oid))
      result->merge = 1;

    /*
     * Merge modes
     */
    if (a->mode == b->mode || a->mode == o->mode)
      result->blob.mode = b->mode;
    else {
      result->blob.mode = a->mode;
      if (b->mode != o->mode) {
        result->clean = 0;
        result->merge = 1;
      }
    }

    if (oideq(&a->oid, &b->oid) || oideq(&a->oid, &o->oid))
      oidcpy(&result->blob.oid, &b->oid);
    else if (oideq(&b->oid, &o->oid))
      oidcpy(&result->blob.oid, &a->oid);
    else if (S_ISREG(a->mode)) {
      mmbuffer_t result_buf;
      int ret = 0, merge_status;

      merge_status = merge_3way(opt, &result_buf, o, a, b,
              branch1, branch2,
              extra_marker_size);

      if ((merge_status < 0) || !result_buf.ptr)
        ret = err(opt, _("failed to execute internal merge"));

      if (!ret &&
          write_object_file(result_buf.ptr, result_buf.size,
                OBJ_BLOB, &result->blob.oid))
        ret = err(opt, _("unable to add %s to database"),
            a->path);

      free(result_buf.ptr);
      if (ret)
        return ret;
      /* FIXME: bug, what if modes didn't match? */
      result->clean = (merge_status == 0);
    } else if (S_ISGITLINK(a->mode)) {
      int clean = merge_submodule(opt, &result->blob.oid,
                o->path,
                &o->oid,
                &a->oid,
                &b->oid);
      if (clean < 0)
        return -1;
      result->clean = clean;
    } else if (S_ISLNK(a->mode)) {
      switch (opt->recursive_variant) {
      case MERGE_VARIANT_NORMAL:
        oidcpy(&result->blob.oid, &a->oid);
        if (!oideq(&a->oid, &b->oid))
          result->clean = 0;
        break;
      case MERGE_VARIANT_OURS:
        oidcpy(&result->blob.oid, &a->oid);
        break;
      case MERGE_VARIANT_THEIRS:
        oidcpy(&result->blob.oid, &b->oid);
        break;
      }
    } else
      BUG("unsupported object type in the tree");
  }

  if (result->merge)
    output(opt, 2, _("Auto-merging %s"), filename);

  return 0;
}

static int handle_rename_via_dir(struct merge_options *opt,
         struct rename_conflict_info *ci)
{
  /*
   * Handle file adds that need to be renamed due to directory rename
   * detection.  This differs from handle_rename_normal, because
   * there is no content merge to do; just move the file into the
   * desired final location.
   */
  const struct rename *ren = ci->ren1;
  const struct diff_filespec *dest = ren->pair->two;
  char *file_path = dest->path;
  int mark_conflicted = (opt->detect_directory_renames ==
             MERGE_DIRECTORY_RENAMES_CONFLICT);
  assert(ren->dir_rename_original_dest);

  if (!opt->priv->call_depth && would_lose_untracked(opt, dest->path)) {
    mark_conflicted = 1;
    file_path = unique_path(opt, dest->path, ren->branch);
    output(opt, 1, _("Error: Refusing to lose untracked file at %s; "
         "writing to %s instead."),
           dest->path, file_path);
  }

  if (mark_conflicted) {
    /*
     * Write the file in worktree at file_path.  In the index,
     * only record the file at dest->path in the appropriate
     * higher stage.
     */
    if (update_file(opt, 0, dest, file_path))
      return -1;
    if (file_path != dest->path)
      free(file_path);
    if (update_stages(opt, dest->path, NULL,
          ren->branch == opt->branch1 ? dest : NULL,
          ren->branch == opt->branch1 ? NULL : dest))
      return -1;
    return 0; /* not clean, but conflicted */
  } else {
    /* Update dest->path both in index and in worktree */
    if (update_file(opt, 1, dest, dest->path))
      return -1;
    return 1; /* clean */
  }
}

static int handle_change_delete(struct merge_options *opt,
        const char *path, const char *old_path,
        const struct diff_filespec *o,
        const struct diff_filespec *changed,
        const char *change_branch,
        const char *delete_branch,
        const char *change, const char *change_past)
{
  char *alt_path = NULL;
  const char *update_path = path;
  int ret = 0;

  if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0) ||
      (!opt->priv->call_depth && would_lose_untracked(opt, path))) {
    update_path = alt_path = unique_path(opt, path, change_branch);
  }

  if (opt->priv->call_depth) {
    /*
     * We cannot arbitrarily accept either a_sha or b_sha as
     * correct; since there is no true "middle point" between
     * them, simply reuse the base version for virtual merge base.
     */
    ret = remove_file_from_index(opt->repo->index, path);
    if (!ret)
      ret = update_file(opt, 0, o, update_path);
  } else {
    /*
     * Despite the four nearly duplicate messages and argument
     * lists below and the ugliness of the nested if-statements,
     * having complete messages makes the job easier for
     * translators.
     *
     * The slight variance among the cases is due to the fact
     * that:
     *   1) directory/file conflicts (in effect if
     *      !alt_path) could cause us to need to write the
     *      file to a different path.
     *   2) renames (in effect if !old_path) could mean that
     *      there are two names for the path that the user
     *      may know the file by.
     */
    if (!alt_path) {
      if (!old_path) {
        output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
               "and %s in %s. Version %s of %s left in tree."),
               change, path, delete_branch, change_past,
               change_branch, change_branch, path);
      } else {
        output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
               "and %s to %s in %s. Version %s of %s left in tree."),
               change, old_path, delete_branch, change_past, path,
               change_branch, change_branch, path);
      }
    } else {
      if (!old_path) {
        output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
               "and %s in %s. Version %s of %s left in tree at %s."),
               change, path, delete_branch, change_past,
               change_branch, change_branch, path, alt_path);
      } else {
        output(opt, 1, _("CONFLICT (%s/delete): %s deleted in %s "
               "and %s to %s in %s. Version %s of %s left in tree at %s."),
               change, old_path, delete_branch, change_past, path,
               change_branch, change_branch, path, alt_path);
      }
    }
    /*
     * No need to call update_file() on path when change_branch ==
     * opt->branch1 && !alt_path, since that would needlessly touch
     * path.  We could call update_file_flags() with update_cache=0
     * and update_wd=0, but that's a no-op.
     */
    if (change_branch != opt->branch1 || alt_path)
      ret = update_file(opt, 0, changed, update_path);
  }
  free(alt_path);

  return ret;
}

static int handle_rename_delete(struct merge_options *opt,
        struct rename_conflict_info *ci)
{
  const struct rename *ren = ci->ren1;
  const struct diff_filespec *orig = ren->pair->one;
  const struct diff_filespec *dest = ren->pair->two;
  const char *rename_branch = ren->branch;
  const char *delete_branch = (opt->branch1 == ren->branch ?
             opt->branch2 : opt->branch1);

  if (handle_change_delete(opt,
         opt->priv->call_depth ? orig->path : dest->path,
         opt->priv->call_depth ? NULL : orig->path,
         orig, dest,
         rename_branch, delete_branch,
         _("rename"), _("renamed")))
    return -1;

  if (opt->priv->call_depth)
    return remove_file_from_index(opt->repo->index, dest->path);
  else
    return update_stages(opt, dest->path, NULL,
             rename_branch == opt->branch1 ? dest : NULL,
             rename_branch == opt->branch1 ? NULL : dest);
}

static int handle_file_collision(struct merge_options *opt,
         const char *collide_path,
         const char *prev_path1,
         const char *prev_path2,
         const char *branch1, const char *branch2,
         struct diff_filespec *a,
         struct diff_filespec *b)
{
  struct merge_file_info mfi;
  struct diff_filespec null;
  char *alt_path = NULL;
  const char *update_path = collide_path;

  /*
   * It's easiest to get the correct things into stage 2 and 3, and
   * to make sure that the content merge puts HEAD before the other
   * branch if we just ensure that branch1 == opt->branch1.  So, simply
   * flip arguments around if we don't have that.
   */
  if (branch1 != opt->branch1) {
    return handle_file_collision(opt, collide_path,
               prev_path2, prev_path1,
               branch2, branch1,
               b, a);
  }

  /* Remove rename sources if rename/add or rename/rename(2to1) */
  if (prev_path1)
    remove_file(opt, 1, prev_path1,
          opt->priv->call_depth || would_lose_untracked(opt, prev_path1));
  if (prev_path2)
    remove_file(opt, 1, prev_path2,
          opt->priv->call_depth || would_lose_untracked(opt, prev_path2));

  /*
   * Remove the collision path, if it wouldn't cause dirty contents
   * or an untracked file to get lost.  We'll either overwrite with
   * merged contents, or just write out to differently named files.
   */
  if (was_dirty(opt, collide_path)) {
    output(opt, 1, _("Refusing to lose dirty file at %s"),
           collide_path);
    update_path = alt_path = unique_path(opt, collide_path, "merged");
  } else if (would_lose_untracked(opt, collide_path)) {
    /*
     * Only way we get here is if both renames were from
     * a directory rename AND user had an untracked file
     * at the location where both files end up after the
     * two directory renames.  See testcase 10d of t6043.
     */
    output(opt, 1, _("Refusing to lose untracked file at "
             "%s, even though it's in the way."),
           collide_path);
    update_path = alt_path = unique_path(opt, collide_path, "merged");
  } else {
    /*
     * FIXME: It's possible that the two files are identical
     * and that the current working copy happens to match, in
     * which case we are unnecessarily touching the working
     * tree file.  It's not a likely enough scenario that I
     * want to code up the checks for it and a better fix is
     * available if we restructure how unpack_trees() and
     * merge-recursive interoperate anyway, so punting for
     * now...
     */
    remove_file(opt, 0, collide_path, 0);
  }

  /* Store things in diff_filespecs for functions that need it */
  null.path = (char *)collide_path;
  oidcpy(&null.oid, null_oid());
  null.mode = 0;

  if (merge_mode_and_contents(opt, &null, a, b, collide_path,
            branch1, branch2, opt->priv->call_depth * 2, &mfi))
    return -1;
  mfi.clean &= !alt_path;
  if (update_file(opt, mfi.clean, &mfi.blob, update_path))
    return -1;
  if (!mfi.clean && !opt->priv->call_depth &&
      update_stages(opt, collide_path, NULL, a, b))
    return -1;
  free(alt_path);
  /*
   * FIXME: If both a & b both started with conflicts (only possible
   * if they came from a rename/rename(2to1)), but had IDENTICAL
   * contents including those conflicts, then in the next line we claim
   * it was clean.  If someone cares about this case, we should have the
   * caller notify us if we started with conflicts.
   */
  return mfi.clean;
}

static int handle_rename_add(struct merge_options *opt,
           struct rename_conflict_info *ci)
{
  /* a was renamed to c, and a separate c was added. */
  struct diff_filespec *a = ci->ren1->pair->one;
  struct diff_filespec *c = ci->ren1->pair->two;
  char *path = c->path;
  char *prev_path_desc;
  struct merge_file_info mfi;

  const char *rename_branch = ci->ren1->branch;
  const char *add_branch = (opt->branch1 == rename_branch ?
          opt->branch2 : opt->branch1);
  int other_stage = (ci->ren1->branch == opt->branch1 ? 3 : 2);

  output(opt, 1, _("CONFLICT (rename/add): "
         "Rename %s->%s in %s.  Added %s in %s"),
         a->path, c->path, rename_branch,
         c->path, add_branch);

  prev_path_desc = xstrfmt("version of %s from %s", path, a->path);
  ci->ren1->src_entry->stages[other_stage].path = a->path;
  if (merge_mode_and_contents(opt, a, c,
            &ci->ren1->src_entry->stages[other_stage],
            prev_path_desc,
            opt->branch1, opt->branch2,
            1 + opt->priv->call_depth * 2, &mfi))
    return -1;
  free(prev_path_desc);

  ci->ren1->dst_entry->stages[other_stage].path = mfi.blob.path = c->path;
  return handle_file_collision(opt,
             c->path, a->path, NULL,
             rename_branch, add_branch,
             &mfi.blob,
             &ci->ren1->dst_entry->stages[other_stage]);
}

static char *find_path_for_conflict(struct merge_options *opt,
            const char *path,
            const char *branch1,
            const char *branch2)
{
  char *new_path = NULL;
  if (dir_in_way(opt->repo->index, path, !opt->priv->call_depth, 0)) {
    new_path = unique_path(opt, path, branch1);
    output(opt, 1, _("%s is a directory in %s adding "
             "as %s instead"),
           path, branch2, new_path);
  } else if (would_lose_untracked(opt, path)) {
    new_path = unique_path(opt, path, branch1);
    output(opt, 1, _("Refusing to lose untracked file"
             " at %s; adding as %s instead"),
           path, new_path);
  }

  return new_path;
}

/*
 * Toggle the stage number between "ours" and "theirs" (2 and 3).
 */
static inline int flip_stage(int stage)
{
  return (2 + 3) - stage;
}

static int handle_rename_rename_1to2(struct merge_options *opt,
             struct rename_conflict_info *ci)
{
  /* One file was renamed in both branches, but to different names. */
  struct merge_file_info mfi;
  struct diff_filespec *add;
  struct diff_filespec *o = ci->ren1->pair->one;
  struct diff_filespec *a = ci->ren1->pair->two;
  struct diff_filespec *b = ci->ren2->pair->two;
  char *path_desc;

  output(opt, 1, _("CONFLICT (rename/rename): "
         "Rename \"%s\"->\"%s\" in branch \"%s\" "
         "rename \"%s\"->\"%s\" in \"%s\"%s"),
         o->path, a->path, ci->ren1->branch,
         o->path, b->path, ci->ren2->branch,
         opt->priv->call_depth ? _(" (left unresolved)") : "");

  path_desc = xstrfmt("%s and %s, both renamed from %s",
          a->path, b->path, o->path);
  if (merge_mode_and_contents(opt, o, a, b, path_desc,
            ci->ren1->branch, ci->ren2->branch,
            opt->priv->call_depth * 2, &mfi))
    return -1;
  free(path_desc);

  if (opt->priv->call_depth)
    remove_file_from_index(opt->repo->index, o->path);

  /*
   * For each destination path, we need to see if there is a
   * rename/add collision.  If not, we can write the file out
   * to the specified location.
   */
  add = &ci->ren1->dst_entry->stages[flip_stage(2)];
  if (is_valid(add)) {
    add->path = mfi.blob.path = a->path;
    if (handle_file_collision(opt, a->path,
            NULL, NULL,
            ci->ren1->branch,
            ci->ren2->branch,
            &mfi.blob, add) < 0)
      return -1;
  } else {
    char *new_path = find_path_for_conflict(opt, a->path,
              ci->ren1->branch,
              ci->ren2->branch);
    if (update_file(opt, 0, &mfi.blob,
        new_path ? new_path : a->path))
      return -1;
    free(new_path);
    if (!opt->priv->call_depth &&
        update_stages(opt, a->path, NULL, a, NULL))
      return -1;
  }

  if (!mfi.clean && mfi.blob.mode == a->mode &&
      oideq(&mfi.blob.oid, &a->oid)) {
    /*
     * Getting here means we were attempting to merge a binary
     * blob.  Since we can't merge binaries, the merge algorithm
     * just takes one side.  But we don't want to copy the
     * contents of one side to both paths; we'd rather use the
     * original content at the given path for each path.
     */
    oidcpy(&mfi.blob.oid, &b->oid);
    mfi.blob.mode = b->mode;
  }
  add = &ci->ren2->dst_entry->stages[flip_stage(3)];
  if (is_valid(add)) {
    add->path = mfi.blob.path = b->path;
    if (handle_file_collision(opt, b->path,
            NULL, NULL,
            ci->ren1->branch,
            ci->ren2->branch,
            add, &mfi.blob) < 0)
      return -1;
  } else {
    char *new_path = find_path_for_conflict(opt, b->path,
              ci->ren2->branch,
              ci->ren1->branch);
    if (update_file(opt, 0, &mfi.blob,
        new_path ? new_path : b->path))
      return -1;
    free(new_path);
    if (!opt->priv->call_depth &&
        update_stages(opt, b->path, NULL, NULL, b))
      return -1;
  }

  return 0;
}

static int handle_rename_rename_2to1(struct merge_options *opt,
             struct rename_conflict_info *ci)
{
  /* Two files, a & b, were renamed to the same thing, c. */
  struct diff_filespec *a = ci->ren1->pair->one;
  struct diff_filespec *b = ci->ren2->pair->one;
  struct diff_filespec *c1 = ci->ren1->pair->two;
  struct diff_filespec *c2 = ci->ren2->pair->two;
  char *path = c1->path; /* == c2->path */
  char *path_side_1_desc;
  char *path_side_2_desc;
  struct merge_file_info mfi_c1;
  struct merge_file_info mfi_c2;
  int ostage1, ostage2;

  output(opt, 1, _("CONFLICT (rename/rename): "
         "Rename %s->%s in %s. "
         "Rename %s->%s in %s"),
         a->path, c1->path, ci->ren1->branch,
         b->path, c2->path, ci->ren2->branch);

  path_side_1_desc = xstrfmt("version of %s from %s", path, a->path);
  path_side_2_desc = xstrfmt("version of %s from %s", path, b->path);
  ostage1 = ci->ren1->branch == opt->branch1 ? 3 : 2;
  ostage2 = flip_stage(ostage1);
  ci->ren1->src_entry->stages[ostage1].path = a->path;
  ci->ren2->src_entry->stages[ostage2].path = b->path;
  if (merge_mode_and_contents(opt, a, c1,
            &ci->ren1->src_entry->stages[ostage1],
            path_side_1_desc,
            opt->branch1, opt->branch2,
            1 + opt->priv->call_depth * 2, &mfi_c1) ||
      merge_mode_and_contents(opt, b,
            &ci->ren2->src_entry->stages[ostage2],
            c2, path_side_2_desc,
            opt->branch1, opt->branch2,
            1 + opt->priv->call_depth * 2, &mfi_c2))
    return -1;
  free(path_side_1_desc);
  free(path_side_2_desc);
  mfi_c1.blob.path = path;
  mfi_c2.blob.path = path;

  return handle_file_collision(opt, path, a->path, b->path,
             ci->ren1->branch, ci->ren2->branch,
             &mfi_c1.blob, &mfi_c2.blob);
}

/*
 * Get the diff_filepairs changed between o_tree and tree.
 */
static struct diff_queue_struct *get_diffpairs(struct merge_options *opt,
                 struct tree *o_tree,
                 struct tree *tree)
{
  struct diff_queue_struct *ret;
  struct diff_options opts;

  repo_diff_setup(opt->repo, &opts);
  opts.flags.recursive = 1;
  opts.flags.rename_empty = 0;
  opts.detect_rename = merge_detect_rename(opt);
  /*
   * We do not have logic to handle the detection of copies.  In
   * fact, it may not even make sense to add such logic: would we
   * really want a change to a base file to be propagated through
   * multiple other files by a merge?
   */
  if (opts.detect_rename > DIFF_DETECT_RENAME)
    opts.detect_rename = DIFF_DETECT_RENAME;
  opts.rename_limit = (opt->rename_limit >= 0) ? opt->rename_limit : 7000;
  opts.rename_score = opt->rename_score;
  opts.show_rename_progress = opt->show_rename_progress;
  opts.output_format = DIFF_FORMAT_NO_OUTPUT;
  diff_setup_done(&opts);
  diff_tree_oid(&o_tree->object.oid, &tree->object.oid, "", &opts);
  diffcore_std(&opts);
  if (opts.needed_rename_limit > opt->priv->needed_rename_limit)
    opt->priv->needed_rename_limit = opts.needed_rename_limit;

  ret = xmalloc(sizeof(*ret));
  *ret = diff_queued_diff;

  opts.output_format = DIFF_FORMAT_NO_OUTPUT;
  diff_queued_diff.nr = 0;
  diff_queued_diff.queue = NULL;
  diff_flush(&opts);
  return ret;
}

static int tree_has_path(struct repository *r, struct tree *tree,
       const char *path)
{
  struct object_id hashy;
  unsigned short mode_o;

  return !get_tree_entry(r,
             &tree->object.oid, path,
             &hashy, &mode_o);
}

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

  if (entry->non_unique_new_dir)
    return NULL;

  oldlen = strlen(entry->dir);
  if (entry->new_dir.len == 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++;
  newlen = entry->new_dir.len + (strlen(old_path) - oldlen) + 1;
  strbuf_grow(&new_path, newlen);
  strbuf_addbuf(&new_path, &entry->new_dir);
  strbuf_addstr(&new_path, &old_path[oldlen]);

  return strbuf_detach(&new_path, NULL);
}

static void get_renamed_dir_portion(const char *old_path, const char *new_path,
            char **old_dir, char **new_dir)
{
  char *end_of_old, *end_of_new;

  /* Default return values: NULL, meaning no rename */
  *old_dir = NULL;
  *new_dir = NULL;

  /*
   * For
   *    "a/b/c/d/e/foo.c" -> "a/b/some/thing/else/e/foo.c"
   * the "e/foo.c" part is the same, we just want to know that
   *    "a/b/c/d" was renamed to "a/b/some/thing/else"
   * so, for this example, this function returns "a/b/c/d" in
   * *old_dir and "a/b/some/thing/else" in *new_dir.
   */

  /*
   * If the basename of the file changed, we don't care.  We want
   * to know which portion of the directory, if any, changed.
   */
  end_of_old = strrchr(old_path, '/');
  end_of_new = strrchr(new_path, '/');

  /*
   * If end_of_old is NULL, old_path wasn't in a directory, so there
   * could not be a directory rename (our rule elsewhere that a
   * directory which still exists is not considered to have been
   * renamed means the root directory can never be renamed -- because
   * the root directory always exists).
   */
  if (!end_of_old)
    return; /* Note: *old_dir and *new_dir are still NULL */

  /*
   * If new_path contains no directory (end_of_new is NULL), then we
   * have a rename of old_path's directory to the root directory.
   */
  if (!end_of_new) {
    *old_dir = xstrndup(old_path, end_of_old - old_path);
    *new_dir = xstrdup("");
    return;
  }

  /* Find the first non-matching character traversing backwards */
  while (*--end_of_new == *--end_of_old &&
         end_of_old != old_path &&
         end_of_new != new_path)
    ; /* Do nothing; all in the while loop */

  /*
   * If both got back to the beginning of their strings, then the
   * directory didn't change at all, only the basename did.
   */
  if (end_of_old == old_path && end_of_new == new_path &&
      *end_of_old == *end_of_new)
    return; /* Note: *old_dir and *new_dir are still NULL */

  /*
   * If end_of_new got back to the beginning of its string, and
   * end_of_old got back to the beginning of some subdirectory, then
   * we have a rename/merge of a subdirectory into the root, which
   * needs slightly special handling.
   *
   * Note: There is no need to consider the opposite case, with a
   * rename/merge of the root directory into some subdirectory
   * because as noted above the root directory always exists so it
   * cannot be considered to be renamed.
   */
  if (end_of_new == new_path &&
      end_of_old != old_path && end_of_old[-1] == '/') {
    *old_dir = xstrndup(old_path, --end_of_old - old_path);
    *new_dir = xstrdup("");
    return;
  }

  /*
   * We've found the first non-matching character in the directory
   * paths.  That means the current characters we were looking at
   * were part of the first non-matching subdir name going back from
   * the end of the strings.  Get the whole name by advancing both
   * end_of_old and end_of_new to the NEXT '/' character.  That will
   * represent the entire directory rename.
   *
   * The reason for the increment is cases like
   *    a/b/star/foo/whatever.c -> a/b/tar/foo/random.c
   * After dropping the basename and going back to the first
   * non-matching character, we're now comparing:
   *    a/b/s          and         a/b/
   * and we want to be comparing:
   *    a/b/star/      and         a/b/tar/
   * but without the pre-increment, the one on the right would stay
   * a/b/.
   */
  end_of_old = strchr(++end_of_old, '/');
  end_of_new = strchr(++end_of_new, '/');

  /* Copy the old and new directories into *old_dir and *new_dir. */
  *old_dir = xstrndup(old_path, end_of_old - old_path);
  *new_dir = xstrndup(new_path, end_of_new - new_path);
}

static void remove_hashmap_entries(struct hashmap *dir_renames,
           struct string_list *items_to_remove)
{
  int i;
  struct dir_rename_entry *entry;

  for (i = 0; i < items_to_remove->nr; i++) {
    entry = items_to_remove->items[i].util;
    hashmap_remove(dir_renames, &entry->ent, NULL);
  }
  string_list_clear(items_to_remove, 0);
}

/*
 * See if there is a directory rename for path, and if there are any file
 * level conflicts 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,
           struct dir_rename_entry *entry,
           struct hashmap *collisions,
           struct tree *tree)
{
  char *new_path = NULL;
  struct collision_entry *collision_ent;
  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(entry, path);

  if (!new_path) {
    /* This should only happen when entry->non_unique_new_dir set */
    if (!entry->non_unique_new_dir)
      BUG("entry->non_unique_new_dir not set and !new_path");
    output(opt, 1, _("CONFLICT (directory rename split): "
             "Unclear where to place %s because directory "
             "%s was renamed to multiple other directories, "
             "with no destination getting a majority of the "
             "files."),
           path, entry->dir);
    clean = 0;
    return NULL;
  }

  /*
   * 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.
   */
  collision_ent = collision_find_entry(collisions, new_path);
  if (!collision_ent)
    BUG("collision_ent 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 (collision_ent->reported_already) {
    clean = 0;
  } else if (tree_has_path(opt->repo, tree, new_path)) {
    collision_ent->reported_already = 1;
    strbuf_add_separated_string_list(&collision_paths, ", ",
             &collision_ent->source_files);
    output(opt, 1, _("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 (collision_ent->source_files.nr > 1) {
    collision_ent->reported_already = 1;
    strbuf_add_separated_string_list(&collision_paths, ", ",
             &collision_ent->source_files);
    output(opt, 1, _("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;
}

/*
 * There are a couple things we want to do at the directory level:
 *   1. Check for both sides renaming to the same thing, in order to avoid
 *      implicit renaming of files that should be left in place.  (See
 *      testcase 6b in t6043 for details.)
 *   2. Prune directory renames if there are still files left in the
 *      original directory.  These represent a partial directory rename,
 *      i.e. a rename where only some of the files within the directory
 *      were renamed elsewhere.  (Technically, this could be done earlier
 *      in get_directory_renames(), except that would prevent us from
 *      doing the previous check and thus failing testcase 6b.)
 *   3. Check for rename/rename(1to2) conflicts (at the directory level).
 *      In the future, we could potentially record this info as well and
 *      omit reporting rename/rename(1to2) conflicts for each path within
 *      the affected directories, thus cleaning up the merge output.
 *   NOTE: We do NOT check for rename/rename(2to1) conflicts at the
 *         directory level, because merging directories is fine.  If it
 *         causes conflicts for files within those merged directories, then
 *         that should be detected at the individual path level.
 */
static void handle_directory_level_conflicts(struct merge_options *opt,
               struct hashmap *dir_re_head,
               struct tree *head,
               struct hashmap *dir_re_merge,
               struct tree *merge)
{
  struct hashmap_iter iter;
  struct dir_rename_entry *head_ent;
  struct dir_rename_entry *merge_ent;

  struct string_list remove_from_head = STRING_LIST_INIT_NODUP;
  struct string_list remove_from_merge = STRING_LIST_INIT_NODUP;

  hashmap_for_each_entry(dir_re_head, &iter, head_ent,
        ent /* member name */) {
    merge_ent = dir_rename_find_entry(dir_re_merge, head_ent->dir);
    if (merge_ent &&
        !head_ent->non_unique_new_dir &&
        !merge_ent->non_unique_new_dir &&
        !strbuf_cmp(&head_ent->new_dir, &merge_ent->new_dir)) {
      /* 1. Renamed identically; remove it from both sides */
      string_list_append(&remove_from_head,
             head_ent->dir)->util = head_ent;
      strbuf_release(&head_ent->new_dir);
      string_list_append(&remove_from_merge,
             merge_ent->dir)->util = merge_ent;
      strbuf_release(&merge_ent->new_dir);
    } else if (tree_has_path(opt->repo, head, head_ent->dir)) {
      /* 2. This wasn't a directory rename after all */
      string_list_append(&remove_from_head,
             head_ent->dir)->util = head_ent;
      strbuf_release(&head_ent->new_dir);
    }
  }

  remove_hashmap_entries(dir_re_head, &remove_from_head);
  remove_hashmap_entries(dir_re_merge, &remove_from_merge);

  hashmap_for_each_entry(dir_re_merge, &iter, merge_ent,
        ent /* member name */) {
    head_ent = dir_rename_find_entry(dir_re_head, merge_ent->dir);
    if (tree_has_path(opt->repo, merge, merge_ent->dir)) {
      /* 2. This wasn't a directory rename after all */
      string_list_append(&remove_from_merge,
             merge_ent->dir)->util = merge_ent;
    } else if (head_ent &&
         !head_ent->non_unique_new_dir &&
         !merge_ent->non_unique_new_dir) {
      /* 3. rename/rename(1to2) */
      /*
       * We can assume it's not rename/rename(1to1) because
       * that was case (1), already checked above.  So we
       * know that head_ent->new_dir and merge_ent->new_dir
       * are different strings.
       */
      output(opt, 1, _("CONFLICT (rename/rename): "
               "Rename directory %s->%s in %s. "
               "Rename directory %s->%s in %s"),
             head_ent->dir, head_ent->new_dir.buf, opt->branch1,
             head_ent->dir, merge_ent->new_dir.buf, opt->branch2);
      string_list_append(&remove_from_head,
             head_ent->dir)->util = head_ent;
      strbuf_release(&head_ent->new_dir);
      string_list_append(&remove_from_merge,
             merge_ent->dir)->util = merge_ent;
      strbuf_release(&merge_ent->new_dir);
    }
  }

  remove_hashmap_entries(dir_re_head, &remove_from_head);
  remove_hashmap_entries(dir_re_merge, &remove_from_merge);
}

static struct hashmap *get_directory_renames(struct diff_queue_struct *pairs)
{
  struct hashmap *dir_renames;
  struct hashmap_iter iter;
  struct dir_rename_entry *entry;
  int i;

  /*
   * Typically, we think of a directory rename as all files from a
   * certain directory being moved to a target directory.  However,
   * what if someone first moved two files from the original
   * directory in one commit, and then renamed the directory
   * somewhere else in a later commit?  At merge time, we just know
   * that files from the original directory went to two different
   * places, and that the bulk of them ended up in the same place.
   * We want each directory rename to represent where the bulk of the
   * files from that directory end up; this function exists to find
   * where the bulk of the files went.
   *
   * The first loop below simply iterates through the list of file
   * renames, finding out how often each directory rename pair
   * possibility occurs.
   */
  dir_renames = xmalloc(sizeof(*dir_renames));
  dir_rename_init(dir_renames);
  for (i = 0; i < pairs->nr; ++i) {
    struct string_list_item *item;
    int *count;
    struct diff_filepair *pair = pairs->queue[i];
    char *old_dir, *new_dir;

    /* File not part of directory rename if it wasn't renamed */
    if (pair->status != 'R')
      continue;

    get_renamed_dir_portion(pair->one->path, pair->two->path,
          &old_dir,        &new_dir);
    if (!old_dir)
      /* Directory didn't change at all; ignore this one. */
      continue;

    entry = dir_rename_find_entry(dir_renames, old_dir);
    if (!entry) {
      entry = xmalloc(sizeof(*entry));
      dir_rename_entry_init(entry, old_dir);
      hashmap_put(dir_renames, &entry->ent);
    } else {
      free(old_dir);
    }
    item = string_list_lookup(&entry->possible_new_dirs, new_dir);
    if (!item) {
      item = string_list_insert(&entry->possible_new_dirs,
              new_dir);
      item->util = xcalloc(1, sizeof(int));
    } else {
      free(new_dir);
    }
    count = item->util;
    *count += 1;
  }

  /*
   * For each directory with files moved out of it, we find out which
   * target directory received the most files so we can declare it to
   * be the "winning" target location for the directory rename.  This
   * winner gets recorded in new_dir.  If there is no winner
   * (multiple target directories received the same number of files),
   * we set non_unique_new_dir.  Once we've determined the winner (or
   * that there is no winner), we no longer need possible_new_dirs.
   */
  hashmap_for_each_entry(dir_renames, &iter, entry,
        ent /* member name */) {
    int max = 0;
    int bad_max = 0;
    char *best = NULL;

    for (i = 0; i < entry->possible_new_dirs.nr; i++) {
      int *count = entry->possible_new_dirs.items[i].util;

      if (*count == max)
        bad_max = max;
      else if (*count > max) {
        max = *count;
        best = entry->possible_new_dirs.items[i].string;
      }
    }
    if (bad_max == max)
      entry->non_unique_new_dir = 1;
    else {
      assert(entry->new_dir.len == 0);
      strbuf_addstr(&entry->new_dir, best);
    }
    /*
     * The relevant directory sub-portion of the original full
     * filepaths were xstrndup'ed before inserting into
     * possible_new_dirs, and instead of manually iterating the
     * list and free'ing each, just lie and tell
     * possible_new_dirs that it did the strdup'ing so that it
     * will free them for us.
     */
    entry->possible_new_dirs.strdup_strings = 1;
    string_list_clear(&entry->possible_new_dirs, 1);
  }

  return dir_renames;
}

static struct dir_rename_entry *check_dir_renamed(const char *path,
              struct hashmap *dir_renames)
{
  char *temp = xstrdup(path);
  char *end;
  struct dir_rename_entry *entry = NULL;

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

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

  /*
   * 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 t6043 for examples.
   */
  collision_init(collisions);

  for (i = 0; i < pairs->nr; ++i) {
    struct dir_rename_entry *dir_rename_ent;
    struct collision_entry *collision_ent;
    char *new_path;
    struct diff_filepair *pair = pairs->queue[i];

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

    new_path = apply_dir_rename(dir_rename_ent, pair->two->path);
    if (!new_path)
      /*
       * dir_rename_ent->non_unique_new_path is true, which
       * means there is no directory rename for us to use,
       * which means it won't cause us any additional
       * collisions.
       */
      continue;
    collision_ent = collision_find_entry(collisions, new_path);
    if (!collision_ent) {
      CALLOC_ARRAY(collision_ent, 1);
      hashmap_entry_init(&collision_ent->ent,
            strhash(new_path));
      hashmap_put(collisions, &collision_ent->ent);
      collision_ent->target_file = new_path;
    } else {
      free(new_path);
    }
    string_list_insert(&collision_ent->source_files,
           pair->two->path);
  }
}

static char *check_for_directory_rename(struct merge_options *opt,
          const char *path,
          struct tree *tree,
          struct hashmap *dir_renames,
          struct hashmap *dir_rename_exclusions,
          struct hashmap *collisions,
          int *clean_merge)
{
  char *new_path = NULL;
  struct dir_rename_entry *entry = check_dir_renamed(path, dir_renames);
  struct dir_rename_entry *oentry = NULL;

  if (!entry)
    return new_path;

  /*
   * 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 oentry and dir_rename_exclusions is here.
   *
   * As it turns out, this also prevents N-way transient rename
   * confusion; See testcases 9c and 9d of t6043.
   */
  oentry = dir_rename_find_entry(dir_rename_exclusions, entry->new_dir.buf);
  if (oentry) {
    output(opt, 1, _("WARNING: Avoiding applying %s -> %s rename "
             "to %s, because %s itself was renamed."),
           entry->dir, entry->new_dir.buf, path, entry->new_dir.buf);
  } else {
    new_path = handle_path_level_conflicts(opt, path, entry,
                   collisions, tree);
    *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,
             struct rename *re,
             struct tree *tree,
             struct tree *o_tree,
             struct tree *a_tree,
             struct tree *b_tree,
             struct string_list *entries)
{
  struct string_list_item *item;
  int stage = (tree == a_tree ? 2 : 3);
  int update_wd;

  /*
   * In all cases where we can do directory rename detection,
   * unpack_trees() will have read pair->two->path into the
   * index and the working copy.  We need to remove it so that
   * we can instead place it at new_path.  It is guaranteed to
   * not be untracked (unpack_trees() would have errored out
   * saying the file would have been overwritten), but it might
   * be dirty, though.
   */
  update_wd = !was_dirty(opt, pair->two->path);
  if (!update_wd)
    output(opt, 1, _("Refusing to lose dirty file at %s"),
           pair->two->path);
  remove_file(opt, 1, pair->two->path, !update_wd);

  /* Find or create a new re->dst_entry */
  item = string_list_lookup(entries, new_path);
  if (item) {
    /*
     * Since we're renaming on this side of history, and it's
     * due to a directory rename on the other side of history
     * (which we only allow when the directory in question no
     * longer exists on the other side of history), the
     * original entry for re->dst_entry is no longer
     * necessary...
     */
    re->dst_entry->processed = 1;

    /*
     * ...because we'll be using this new one.
     */
    re->dst_entry = item->util;
  } else {
    /*
     * re->dst_entry is for the before-dir-rename path, and we
     * need it to hold information for the after-dir-rename
     * path.  Before creating a new entry, we need to mark the
     * old one as unnecessary (...unless it is shared by
     * src_entry, i.e. this didn't use to be a rename, in which
     * case we can just allow the normal processing to happen
     * for it).
     */
    if (pair->status == 'R')
      re->dst_entry->processed = 1;

    re->dst_entry = insert_stage_data(opt->repo, new_path,
              o_tree, a_tree, b_tree,
              entries);
    item = string_list_insert(entries, new_path);
    item->util = re->dst_entry;
  }

  /*
   * Update the stage_data with the information about the path we are
   * moving into place.  That slot will be empty and available for us
   * to write to because of the collision checks in
   * handle_path_level_conflicts().  In other words,
   * re->dst_entry->stages[stage].oid will be the null_oid, so it's
   * open for us to write to.
   *
   * It may be tempting to actually update the index at this point as
   * well, using update_stages_for_stage_data(), but as per the big
   * "NOTE" in update_stages(), doing so will modify the current
   * in-memory index which will break calls to would_lose_untracked()
   * that we need to make.  Instead, we need to just make sure that
   * the various handle_rename_*() functions update the index
   * explicitly rather than relying on unpack_trees() to have done it.
   */
  get_tree_entry(opt->repo,
           &tree->object.oid,
           pair->two->path,
           &re->dst_entry->stages[stage].oid,
           &re->dst_entry->stages[stage].mode);

  /*
   * Record the original change status (or 'type' of change).  If it
   * was originally an add ('A'), this lets us differentiate later
   * between a RENAME_DELETE conflict and RENAME_VIA_DIR (they
   * otherwise look the same).  If it was originally a rename ('R'),
   * this lets us remember and report accurately about the transitive
   * renaming that occurred via the directory rename detection.  Also,
   * record the original destination name.
   */
  re->dir_rename_original_type = pair->status;
  re->dir_rename_original_dest = pair->two->path;

  /*
   * We don't actually look at pair->status again, but it seems
   * pedagogically correct to adjust it.
   */
  pair->status = 'R';

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

/*
 * Get information of all renames which occurred in 'pairs', making use of
 * any implicit directory renames inferred from the other side of history.
 * We need the three trees in the merge ('o_tree', 'a_tree' and 'b_tree')
 * to be able to associate the correct cache entries with the rename
 * information; tree is always equal to either a_tree or b_tree.
 */
static struct string_list *get_renames(struct merge_options *opt,
               const char *branch,
               struct diff_queue_struct *pairs,
               struct hashmap *dir_renames,
               struct hashmap *dir_rename_exclusions,
               struct tree *tree,
               struct tree *o_tree,
               struct tree *a_tree,
               struct tree *b_tree,
               struct string_list *entries,
               int *clean_merge)
{
  int i;
  struct hashmap collisions;
  struct hashmap_iter iter;
  struct collision_entry *e;
  struct string_list *renames;

  compute_collisions(&collisions, dir_renames, pairs);
  CALLOC_ARRAY(renames, 1);

  for (i = 0; i < pairs->nr; ++i) {
    struct string_list_item *item;
    struct rename *re;
    struct diff_filepair *pair = pairs->queue[i];
    char *new_path; /* non-NULL only with directory renames */

    if (pair->status != 'A' && pair->status != 'R') {
      diff_free_filepair(pair);
      continue;
    }
    new_path = check_for_directory_rename(opt, pair->two->path, tree,
                  dir_renames,
                  dir_rename_exclusions,
                  &collisions,
                  clean_merge);
    if (pair->status != 'R' && !new_path) {
      diff_free_filepair(pair);
      continue;
    }

    re = xmalloc(sizeof(*re));
    re->processed = 0;
    re->pair = pair;
    re->branch = branch;
    re->dir_rename_original_type = '\0';
    re->dir_rename_original_dest = NULL;
    item = string_list_lookup(entries, re->pair->one->path);
    if (!item)
      re->src_entry = insert_stage_data(opt->repo,
          re->pair->one->path,
          o_tree, a_tree, b_tree, entries);
    else
      re->src_entry = item->util;

    item = string_list_lookup(entries, re->pair->two->path);
    if (!item)
      re->dst_entry = insert_stage_data(opt->repo,
          re->pair->two->path,
          o_tree, a_tree, b_tree, entries);
    else
      re->dst_entry = item->util;
    item = string_list_insert(renames, pair->one->path);
    item->util = re;
    if (new_path)
      apply_directory_rename_modifications(opt, pair, new_path,
                   re, tree, o_tree,
                   a_tree, b_tree,
                   entries);
  }

  hashmap_for_each_entry(&collisions, &iter, e,
        ent /* member name */) {
    free(e->target_file);
    string_list_clear(&e->source_files, 0);
  }
  hashmap_clear_and_free(&collisions, struct collision_entry, ent);
  return renames;
}

static int process_renames(struct merge_options *opt,
         struct string_list *a_renames,
         struct string_list *b_renames)
{
  int clean_merge = 1, i, j;
  struct string_list a_by_dst = STRING_LIST_INIT_NODUP;
  struct string_list b_by_dst = STRING_LIST_INIT_NODUP;
  const struct rename *sre;

  /*
   * FIXME: As string-list.h notes, it's O(n^2) to build a sorted
   * string_list one-by-one, but O(n log n) to build it unsorted and
   * then sort it.  Note that as we build the list, we do not need to
   * check if the existing destination path is already in the list,
   * because the structure of diffcore_rename guarantees we won't
   * have duplicates.
   */
  for (i = 0; i < a_renames->nr; i++) {
    sre = a_renames->items[i].util;
    string_list_insert(&a_by_dst, sre->pair->two->path)->util
      = (void *)sre;
  }
  for (i = 0; i < b_renames->nr; i++) {
    sre = b_renames->items[i].util;
    string_list_insert(&b_by_dst, sre->pair->two->path)->util
      = (void *)sre;
  }

  for (i = 0, j = 0; i < a_renames->nr || j < b_renames->nr;) {
    struct string_list *renames1, *renames2Dst;
    struct rename *ren1 = NULL, *ren2 = NULL;
    const char *ren1_src, *ren1_dst;
    struct string_list_item *lookup;

    if (i >= a_renames->nr) {
      ren2 = b_renames->items[j++].util;
    } else if (j >= b_renames->nr) {
      ren1 = a_renames->items[i++].util;
    } else {
      int compare = strcmp(a_renames->items[i].string,
               b_renames->items[j].string);
      if (compare <= 0)
        ren1 = a_renames->items[i++].util;
      if (compare >= 0)
        ren2 = b_renames->items[j++].util;
    }

    /* TODO: refactor, so that 1/2 are not needed */
    if (ren1) {
      renames1 = a_renames;
      renames2Dst = &b_by_dst;
    } else {
      renames1 = b_renames;
      renames2Dst = &a_by_dst;
      SWAP(ren2, ren1);
    }

    if (ren1->processed)
      continue;
    ren1->processed = 1;
    ren1->dst_entry->processed = 1;
    /* BUG: We should only mark src_entry as processed if we
     * are not dealing with a rename + add-source case.
     */
    ren1->src_entry->processed = 1;

    ren1_src = ren1->pair->one->path;
    ren1_dst = ren1->pair->two->path;

    if (ren2) {
      /* One file renamed on both sides */
      const char *ren2_src = ren2->pair->one->path;
      const char *ren2_dst = ren2->pair->two->path;
      enum rename_type rename_type;
      if (strcmp(ren1_src, ren2_src) != 0)
        BUG("ren1_src != ren2_src");
      ren2->dst_entry->processed = 1;
      ren2->processed = 1;
      if (strcmp(ren1_dst, ren2_dst) != 0) {
        rename_type = RENAME_ONE_FILE_TO_TWO;
        clean_merge = 0;
      } else {
        rename_type = RENAME_ONE_FILE_TO_ONE;
        /* BUG: We should only remove ren1_src in
         * the base stage (think of rename +
         * add-source cases).
         */
        remove_file(opt, 1, ren1_src, 1);
        update_entry(ren1->dst_entry,
               ren1->pair->one,
               ren1->pair->two,
               ren2->pair->two);
      }
      setup_rename_conflict_info(rename_type, opt, ren1, ren2);
    } else if ((lookup = string_list_lookup(renames2Dst, ren1_dst))) {
      /* Two different files renamed to the same thing */
      char *ren2_dst;
      ren2 = lookup->util;
      ren2_dst = ren2->pair->two->path;
      if (strcmp(ren1_dst, ren2_dst) != 0)
        BUG("ren1_dst != ren2_dst");

      clean_merge = 0;
      ren2->processed = 1;
      /*
       * BUG: We should only mark src_entry as processed
       * if we are not dealing with a rename + add-source
       * case.
       */
      ren2->src_entry->processed = 1;

      setup_rename_conflict_info(RENAME_TWO_FILES_TO_ONE,
               opt, ren1, ren2);
    } else {
      /* Renamed in 1, maybe changed in 2 */
      /* we only use sha1 and mode of these */
      struct diff_filespec src_other, dst_other;
      int try_merge;

      /*
       * unpack_trees loads entries from common-commit
       * into stage 1, from head-commit into stage 2, and
       * from merge-commit into stage 3.  We keep track
       * of which side corresponds to the rename.
       */
      int renamed_stage = a_renames == renames1 ? 2 : 3;
      int other_stage =   a_renames == renames1 ? 3 : 2;

      /*
       * Directory renames have a funny corner case...
       */
      int renamed_to_self = !strcmp(ren1_src, ren1_dst);

      /* BUG: We should only remove ren1_src in the base
       * stage and in other_stage (think of rename +
       * add-source case).
       */
      if (!renamed_to_self)
        remove_file(opt, 1, ren1_src,
              renamed_stage == 2 ||
              !was_tracked(opt, ren1_src));

      oidcpy(&src_other.oid,
             &ren1->src_entry->stages[other_stage].oid);
      src_other.mode = ren1->src_entry->stages[other_stage].mode;
      oidcpy(&dst_other.oid,
             &ren1->dst_entry->stages[other_stage].oid);
      dst_other.mode = ren1->dst_entry->stages[other_stage].mode;
      try_merge = 0;

      if (oideq(&src_other.oid, null_oid()) &&
          ren1->dir_rename_original_type == 'A') {
        setup_rename_conflict_info(RENAME_VIA_DIR,
                 opt, ren1, NULL);
      } else if (renamed_to_self) {
        setup_rename_conflict_info(RENAME_NORMAL,
                 opt, ren1, NULL);
      } else if (oideq(&src_other.oid, null_oid())) {
        setup_rename_conflict_info(RENAME_DELETE,
                 opt, ren1, NULL);
      } else if ((dst_other.mode == ren1->pair->two->mode) &&
           oideq(&dst_other.oid, &ren1->pair->two->oid)) {
        /*
         * Added file on the other side identical to
         * the file being renamed: clean merge.
         * Also, there is no need to overwrite the
         * file already in the working copy, so call
         * update_file_flags() instead of
         * update_file().
         */
        if (update_file_flags(opt,
                  ren1->pair->two,
                  ren1_dst,
                  1, /* update_cache */
                  0  /* update_wd    */))
          clean_merge = -1;
      } else if (!oideq(&dst_other.oid, null_oid())) {
        /*
         * Probably not a clean merge, but it's
         * premature to set clean_merge to 0 here,
         * because if the rename merges cleanly and
         * the merge exactly matches the newly added
         * file, then the merge will be clean.
         */
        setup_rename_conflict_info(RENAME_ADD,
                 opt, ren1, NULL);
      } else
        try_merge = 1;

      if (clean_merge < 0)
        goto cleanup_and_return;
      if (try_merge) {
        struct diff_filespec *o, *a, *b;
        src_other.path = (char *)ren1_src;

        o = ren1->pair->one;
        if (a_renames == renames1) {
          a = ren1->pair->two;
          b = &src_other;
        } else {
          b = ren1->pair->two;
          a = &src_other;
        }
        update_entry(ren1->dst_entry, o, a, b);
        setup_rename_conflict_info(RENAME_NORMAL,
                 opt, ren1, NULL);
      }
    }
  }
cleanup_and_return:
  string_list_clear(&a_by_dst, 0);
  string_list_clear(&b_by_dst, 0);

  return clean_merge;
}

struct rename_info {
  struct string_list *head_renames;
  struct string_list *merge_renames;
};

static void initial_cleanup_rename(struct diff_queue_struct *pairs,
           struct hashmap *dir_renames)
{
  struct hashmap_iter iter;
  struct dir_rename_entry *e;

  hashmap_for_each_entry(dir_renames, &iter, e,
        ent /* member name */) {
    free(e->dir);
    strbuf_release(&e->new_dir);
    /* possible_new_dirs already cleared in get_directory_renames */
  }
  hashmap_clear_and_free(dir_renames, struct dir_rename_entry, ent);
  free(dir_renames);

  free(pairs->queue);
  free(pairs);
}

static int detect_and_process_renames(struct merge_options *opt,
              struct tree *common,
              struct tree *head,
              struct tree *merge,
              struct string_list *entries,
              struct rename_info *ri)
{
  struct diff_queue_struct *head_pairs, *merge_pairs;
  struct hashmap *dir_re_head, *dir_re_merge;
  int clean = 1;

  ri->head_renames = NULL;
  ri->merge_renames = NULL;

  if (!merge_detect_rename(opt))
    return 1;

  head_pairs = get_diffpairs(opt, common, head);
  merge_pairs = get_diffpairs(opt, common, merge);

  if ((opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE) ||
      (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT &&
       !opt->priv->call_depth)) {
    dir_re_head = get_directory_renames(head_pairs);
    dir_re_merge = get_directory_renames(merge_pairs);

    handle_directory_level_conflicts(opt,
             dir_re_head, head,
             dir_re_merge, merge);
  } else {
    dir_re_head  = xmalloc(sizeof(*dir_re_head));
    dir_re_merge = xmalloc(sizeof(*dir_re_merge));
    dir_rename_init(dir_re_head);
    dir_rename_init(dir_re_merge);
  }

  ri->head_renames  = get_renames(opt, opt->branch1, head_pairs,
          dir_re_merge, dir_re_head, head,
          common, head, merge, entries,
          &clean);
  if (clean < 0)
    goto cleanup;
  ri->merge_renames = get_renames(opt, opt->branch2, merge_pairs,
          dir_re_head, dir_re_merge, merge,
          common, head, merge, entries,
          &clean);
  if (clean < 0)
    goto cleanup;
  clean &= process_renames(opt, ri->head_renames, ri->merge_renames);

cleanup:
  /*
   * Some cleanup is deferred until cleanup_renames() because the
   * data structures are still needed and referenced in
   * process_entry().  But there are a few things we can free now.
   */
  initial_cleanup_rename(head_pairs, dir_re_head);
  initial_cleanup_rename(merge_pairs, dir_re_merge);

  return clean;
}

static void final_cleanup_rename(struct string_list *rename)
{
  const struct rename *re;
  int i;

  if (!rename)
    return;

  for (i = 0; i < rename->nr; i++) {
    re = rename->items[i].util;
    diff_free_filepair(re->pair);
    if (re->src_entry->rename_conflict_info_owned)
      FREE_AND_NULL(re->src_entry->rename_conflict_info);
    if (re->dst_entry->rename_conflict_info_owned)
      FREE_AND_NULL(re->dst_entry->rename_conflict_info);
  }
  string_list_clear(rename, 1);
  free(rename);
}

static void final_cleanup_renames(struct rename_info *re_info)
{
  final_cleanup_rename(re_info->head_renames);
  final_cleanup_rename(re_info->merge_renames);
}

static int read_oid_strbuf(struct merge_options *opt,
         const struct object_id *oid,
         struct strbuf *dst)
{
  void *buf;
  enum object_type type;
  unsigned long size;
  buf = repo_read_object_file(the_repository, oid, &type, &size);
  if (!buf)
    return err(opt, _("cannot read object %s"), oid_to_hex(oid));
  if (type != OBJ_BLOB) {
    free(buf);
    return err(opt, _("object %s is not a blob"), oid_to_hex(oid));
  }
  strbuf_attach(dst, buf, size, size + 1);
  return 0;
}

static int blob_unchanged(struct merge_options *opt,
        const struct diff_filespec *o,
        const struct diff_filespec *a,
        int renormalize, const char *path)
{
  struct strbuf obuf = STRBUF_INIT;
  struct strbuf abuf = STRBUF_INIT;
  int ret = 0; /* assume changed for safety */
  struct index_state *idx = opt->repo->index;

  if (a->mode != o->mode)
    return 0;
  if (oideq(&o->oid, &a->oid))
    return 1;
  if (!renormalize)
    return 0;

  if (read_oid_strbuf(opt, &o->oid, &obuf) ||
      read_oid_strbuf(opt, &a->oid, &abuf))
    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, obuf.buf, obuf.len, &obuf) |
      renormalize_buffer(idx, path, abuf.buf, abuf.len, &abuf))
    ret = (obuf.len == abuf.len && !memcmp(obuf.buf, abuf.buf, obuf.len));

error_return:
  strbuf_release(&obuf);
  strbuf_release(&abuf);
  return ret;
}

static int handle_modify_delete(struct merge_options *opt,
        const char *path,
        const struct diff_filespec *o,
        const struct diff_filespec *a,
        const struct diff_filespec *b)
{
  const char *modify_branch, *delete_branch;
  const struct diff_filespec *changed;

  if (is_valid(a)) {
    modify_branch = opt->branch1;
    delete_branch = opt->branch2;
    changed = a;
  } else {
    modify_branch = opt->branch2;
    delete_branch = opt->branch1;
    changed = b;
  }

  return handle_change_delete(opt,
            path, NULL,
            o, changed,
            modify_branch, delete_branch,
            _("modify"), _("modified"));
}

static int handle_content_merge(struct merge_file_info *mfi,
        struct merge_options *opt,
        const char *path,
        int is_dirty,
        const struct diff_filespec *o,
        const struct diff_filespec *a,
        const struct diff_filespec *b,
        struct rename_conflict_info *ci)
{
  const char *reason = _("content");
  unsigned df_conflict_remains = 0;

  if (!is_valid(o))
    reason = _("add/add");

  assert(o->path && a->path && b->path);
  if (ci && dir_in_way(opt->repo->index, path, !opt->priv->call_depth,
           S_ISGITLINK(ci->ren1->pair->two->mode)))
    df_conflict_remains = 1;

  if (merge_mode_and_contents(opt, o, a, b, path,
            opt->branch1, opt->branch2,
            opt->priv->call_depth * 2, mfi))
    return -1;

  /*
   * We can skip updating the working tree file iff:
   *   a) The merge is clean
   *   b) The merge matches what was in HEAD (content, mode, pathname)
   *   c) The target path is usable (i.e. not involved in D/F conflict)
   */
  if (mfi->clean && was_tracked_and_matches(opt, path, &mfi->blob) &&
      !df_conflict_remains) {
    int pos;
    struct cache_entry *ce;

    output(opt, 3, _("Skipped %s (merged same as existing)"), path);
    if (add_cacheinfo(opt, &mfi->blob, path,
          0, (!opt->priv->call_depth && !is_dirty), 0))
      return -1;
    /*
     * However, add_cacheinfo() will delete the old cache entry
     * and add a new one.  We need to copy over any skip_worktree
     * flag to avoid making the file appear as if it were
     * deleted by the user.
     */
    pos = index_name_pos(&opt->priv->orig_index, path, strlen(path));
    ce = opt->priv->orig_index.cache[pos];
    if (ce_skip_worktree(ce)) {
      pos = index_name_pos(opt->repo->index, path, strlen(path));
      ce = opt->repo->index->cache[pos];
      ce->ce_flags |= CE_SKIP_WORKTREE;
    }
    return mfi->clean;
  }

  if (!mfi->clean) {
    if (S_ISGITLINK(mfi->blob.mode))
      reason = _("submodule");
    output(opt, 1, _("CONFLICT (%s): Merge conflict in %s"),
        reason, path);
    if (ci && !df_conflict_remains)
      if (update_stages(opt, path, o, a, b))
        return -1;
  }

  if (df_conflict_remains || is_dirty) {
    char *new_path;
    if (opt->priv->call_depth) {
      remove_file_from_index(opt->repo->index, path);
    } else {
      if (!mfi->clean) {
        if (update_stages(opt, path, o, a, b))
          return -1;
      } else {
        int file_from_stage2 = was_tracked(opt, path);

        if (update_stages(opt, path, NULL,
              file_from_stage2 ? &mfi->blob : NULL,
              file_from_stage2 ? NULL : &mfi->blob))
          return -1;
      }

    }
    new_path = unique_path(opt, path, ci->ren1->branch);
    if (is_dirty) {
      output(opt, 1, _("Refusing to lose dirty file at %s"),
             path);
    }
    output(opt, 1, _("Adding as %s instead"), new_path);
    if (update_file(opt, 0, &mfi->blob, new_path)) {
      free(new_path);
      return -1;
    }
    free(new_path);
    mfi->clean = 0;
  } else if (update_file(opt, mfi->clean, &mfi->blob, path))
    return -1;
  return !is_dirty && mfi->clean;
}

static int handle_rename_normal(struct merge_options *opt,
        const char *path,
        const struct diff_filespec *o,
        const struct diff_filespec *a,
        const struct diff_filespec *b,
        struct rename_conflict_info *ci)
{
  struct rename *ren = ci->ren1;
  struct merge_file_info mfi;
  int clean;

  /* Merge the content and write it out */
  clean = handle_content_merge(&mfi, opt, path, was_dirty(opt, path),
             o, a, b, ci);

  if (clean &&
      opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_CONFLICT &&
      ren->dir_rename_original_dest) {
    if (update_stages(opt, path,
          &mfi.blob, &mfi.blob, &mfi.blob))
      return -1;
    clean = 0; /* not clean, but conflicted */
  }
  return clean;
}

static void dir_rename_warning(const char *msg,
             int is_add,
             int clean,
             struct merge_options *opt,
             struct rename *ren)
{
  const char *other_branch;
  other_branch = (ren->branch == opt->branch1 ?
      opt->branch2 : opt->branch1);
  if (is_add) {
    output(opt, clean ? 2 : 1, msg,
           ren->pair->one->path, ren->branch,
           other_branch, ren->pair->two->path);
    return;
  }
  output(opt, clean ? 2 : 1, msg,
         ren->pair->one->path, ren->dir_rename_original_dest, ren->branch,
         other_branch, ren->pair->two->path);
}
static int warn_about_dir_renamed_entries(struct merge_options *opt,
            struct rename *ren)
{
  const char *msg;
  int clean = 1, is_add;

  if (!ren)
    return clean;

  /* Return early if ren was not affected/created by a directory rename */
  if (!ren->dir_rename_original_dest)
    return clean;

  /* Sanity checks */
  assert(opt->detect_directory_renames > MERGE_DIRECTORY_RENAMES_NONE);
  assert(ren->dir_rename_original_type == 'A' ||
         ren->dir_rename_original_type == 'R');

  /* Check whether to treat directory renames as a conflict */
  clean = (opt->detect_directory_renames == MERGE_DIRECTORY_RENAMES_TRUE);

  is_add = (ren->dir_rename_original_type == 'A');
  if (ren->dir_rename_original_type == 'A' && clean) {
    msg = _("Path updated: %s added in %s inside a "
      "directory that was renamed in %s; moving it to %s.");
  } else if (ren->dir_rename_original_type == 'A' && !clean) {
    msg = _("CONFLICT (file location): %s added in %s "
      "inside a directory that was renamed in %s, "
      "suggesting it should perhaps be moved to %s.");
  } else if (ren->dir_rename_original_type == 'R' && clean) {
    msg = _("Path updated: %s renamed to %s in %s, inside a "
      "directory that was renamed in %s; moving it to %s.");
  } else if (ren->dir_rename_original_type == 'R' && !clean) {
    msg = _("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.");
  } else {
    BUG("Impossible dir_rename_original_type/clean combination");
  }
  dir_rename_warning(msg, is_add, clean, opt, ren);

  return clean;
}

/* Per entry merge function */
static int process_entry(struct merge_options *opt,
       const char *path, struct stage_data *entry)
{
  int clean_merge = 1;
  int normalize = opt->renormalize;

  struct diff_filespec *o = &entry->stages[1];
  struct diff_filespec *a = &entry->stages[2];
  struct diff_filespec *b = &entry->stages[3];
  int o_valid = is_valid(o);
  int a_valid = is_valid(a);
  int b_valid = is_valid(b);
  o->path = a->path = b->path = (char*)path;

  entry->processed = 1;
  if (entry->rename_conflict_info) {
    struct rename_conflict_info *ci = entry->rename_conflict_info;
    struct diff_filespec *temp;
    int path_clean;

    path_clean = warn_about_dir_renamed_entries(opt, ci->ren1);
    path_clean &= warn_about_dir_renamed_entries(opt, ci->ren2);

    /*
     * For cases with a single rename, {o,a,b}->path have all been
     * set to the rename target path; we need to set two of these
     * back to the rename source.
     * For rename/rename conflicts, we'll manually fix paths below.
     */
    temp = (opt->branch1 == ci->ren1->branch) ? b : a;
    o->path = temp->path = ci->ren1->pair->one->path;
    if (ci->ren2) {
      assert(opt->branch1 == ci->ren1->branch);
    }

    switch (ci->rename_type) {
    case RENAME_NORMAL:
    case RENAME_ONE_FILE_TO_ONE:
      clean_merge = handle_rename_normal(opt, path, o, a, b,
                 ci);
      break;
    case RENAME_VIA_DIR:
      clean_merge = handle_rename_via_dir(opt, ci);
      break;
    case RENAME_ADD:
      /*
       * Probably unclean merge, but if the renamed file
       * merges cleanly and the result can then be
       * two-way merged cleanly with the added file, I
       * guess it's a clean merge?
       */
      clean_merge = handle_rename_add(opt, ci);
      break;
    case RENAME_DELETE:
      clean_merge = 0;
      if (handle_rename_delete(opt, ci))
        clean_merge = -1;
      break;
    case RENAME_ONE_FILE_TO_TWO:
      /*
       * Manually fix up paths; note:
       * ren[12]->pair->one->path are equal.
       */
      o->path = ci->ren1->pair->one->path;
      a->path = ci->ren1->pair->two->path;
      b->path = ci->ren2->pair->two->path;

      clean_merge = 0;
      if (handle_rename_rename_1to2(opt, ci))
        clean_merge = -1;
      break;
    case RENAME_TWO_FILES_TO_ONE:
      /*
       * Manually fix up paths; note,
       * ren[12]->pair->two->path are actually equal.
       */
      o->path = NULL;
      a->path = ci->ren1->pair->two->path;
      b->path = ci->ren2->pair->two->path;

      /*
       * Probably unclean merge, but if the two renamed
       * files merge cleanly and the two resulting files
       * can then be two-way merged cleanly, I guess it's
       * a clean merge?
       */
      clean_merge = handle_rename_rename_2to1(opt, ci);
      break;
    default:
      entry->processed = 0;
      break;
    }
    if (path_clean < clean_merge)
      clean_merge = path_clean;
  } else if (o_valid && (!a_valid || !b_valid)) {
    /* Case A: Deleted in one */
    if ((!a_valid && !b_valid) ||
        (!b_valid && blob_unchanged(opt, o, a, normalize, path)) ||
        (!a_valid && blob_unchanged(opt, o, b, normalize, path))) {
      /* Deleted in both or deleted in one and
       * unchanged in the other */
      if (a_valid)
        output(opt, 2, _("Removing %s"), path);
      /* do not touch working file if it did not exist */
      remove_file(opt, 1, path, !a_valid);
    } else {
      /* Modify/delete; deleted side may have put a directory in the way */
      clean_merge = 0;
      if (handle_modify_delete(opt, path, o, a, b))
        clean_merge = -1;
    }
  } else if ((!o_valid && a_valid && !b_valid) ||
       (!o_valid && !a_valid && b_valid)) {
    /* Case B: Added in one. */
    /* [nothing|directory] -> ([nothing|directory], file) */

    const char *add_branch;
    const char *other_branch;
    const char *conf;
    const struct diff_filespec *contents;

    if (a_valid) {
      add_branch = opt->branch1;
      other_branch = opt->branch2;
      contents = a;
      conf = _("file/directory");
    } else {
      add_branch = opt->branch2;
      other_branch = opt->branch1;
      contents = b;
      conf = _("directory/file");
    }
    if (dir_in_way(opt->repo->index, path,
             !opt->priv->call_depth && !S_ISGITLINK(a->mode),
             0)) {
      char *new_path = unique_path(opt, path, add_branch);
      clean_merge = 0;
      output(opt, 1, _("CONFLICT (%s): There is a directory with name %s in %s. "
             "Adding %s as %s"),
             conf, path, other_branch, path, new_path);
      if (update_file(opt, 0, contents, new_path))
        clean_merge = -1;
      else if (opt->priv->call_depth)
        remove_file_from_index(opt->repo->index, path);
      free(new_path);
    } else {
      output(opt, 2, _("Adding %s"), path);
      /* do not overwrite file if already present */
      if (update_file_flags(opt, contents, path, 1, !a_valid))
        clean_merge = -1;
    }
  } else if (a_valid && b_valid) {
    if (!o_valid) {
      /* Case C: Added in both (check for same permissions) */
      output(opt, 1,
             _("CONFLICT (add/add): Merge conflict in %s"),
             path);
      clean_merge = handle_file_collision(opt,
                  path, NULL, NULL,
                  opt->branch1,
                  opt->branch2,
                  a, b);
    } else {
      /* case D: Modified in both, but differently. */
      struct merge_file_info mfi;
      int is_dirty = 0; /* unpack_trees would have bailed if dirty */
      clean_merge = handle_content_merge(&mfi, opt, path,
                 is_dirty,
                 o, a, b, NULL);
    }
  } else if (!o_valid && !a_valid && !b_valid) {
    /*
     * this entry was deleted altogether. a_mode == 0 means
     * we had that path and want to actively remove it.
     */
    remove_file(opt, 1, path, !a->mode);
  } else
    BUG("fatal merge failure, shouldn't happen.");

  return clean_merge;
}

static int merge_trees_internal(struct merge_options *opt,
        struct tree *head,
        struct tree *merge,
        struct tree *merge_base,
        struct tree **result)
{
  struct index_state *istate = opt->repo->index;
  int code, clean;

  if (opt->subtree_shift) {
    merge = shift_tree_object(opt->repo, head, merge,
            opt->subtree_shift);
    merge_base = shift_tree_object(opt->repo, head, merge_base,
                 opt->subtree_shift);
  }

  if (oideq(&merge_base->object.oid, &merge->object.oid)) {
    output(opt, 0, _("Already up to date."));
    *result = head;
    return 1;
  }

  code = unpack_trees_start(opt, merge_base, head, merge);

  if (code != 0) {
    if (show(opt, 4) || opt->priv->call_depth)
      err(opt, _("merging of trees %s and %s failed"),
          oid_to_hex(&head->object.oid),
          oid_to_hex(&merge->object.oid));
    unpack_trees_finish(opt);
    return -1;
  }

  if (unmerged_index(istate)) {
    struct string_list *entries;
    struct rename_info re_info;
    int i;
    /*
     * Only need the hashmap while processing entries, so
     * initialize it here and free it when we are done running
     * through the entries. Keeping it in the merge_options as
     * opposed to decaring a local hashmap is for convenience
     * so that we don't have to pass it to around.
     */
    hashmap_init(&opt->priv->current_file_dir_set, path_hashmap_cmp,
           NULL, 512);
    get_files_dirs(opt, head);
    get_files_dirs(opt, merge);

    entries = get_unmerged(opt->repo->index);
    clean = detect_and_process_renames(opt, merge_base, head, merge,
               entries, &re_info);
    record_df_conflict_files(opt, entries);
    if (clean < 0)
      goto cleanup;
    for (i = entries->nr-1; 0 <= i; i--) {
      const char *path = entries->items[i].string;
      struct stage_data *e = entries->items[i].util;
      if (!e->processed) {
        int ret = process_entry(opt, path, e);
        if (!ret)
          clean = 0;
        else if (ret < 0) {
          clean = ret;
          goto cleanup;
        }
      }
    }
    for (i = 0; i < entries->nr; i++) {
      struct stage_data *e = entries->items[i].util;
      if (!e->processed)
        BUG("unprocessed path??? %s",
            entries->items[i].string);
    }

  cleanup:
    final_cleanup_renames(&re_info);

    string_list_clear(entries, 1);
    free(entries);

    hashmap_clear_and_free(&opt->priv->current_file_dir_set,
          struct path_hashmap_entry, e);

    if (clean < 0) {
      unpack_trees_finish(opt);
      return clean;
    }
  }
  else
    clean = 1;

  unpack_trees_finish(opt);

  if (opt->priv->call_depth &&
      !(*result = write_in_core_index_as_tree(opt->repo)))
    return -1;

  return clean;
}

/*
 * Merge the commits h1 and h2, returning a flag (int) indicating the
 * cleanness of the merge.  Also, if opt->priv->call_depth, create a
 * virtual commit and write its location to *result.
 */
static int merge_recursive_internal(struct merge_options *opt,
            struct commit *h1,
            struct commit *h2,
            const struct commit_list *_merge_bases,
            struct commit **result)
{
  struct commit_list *merge_bases = copy_commit_list(_merge_bases);
  struct commit_list *iter;
  struct commit *merged_merge_bases;
  struct tree *result_tree;
  const char *ancestor_name;
  struct strbuf merge_base_abbrev = STRBUF_INIT;
  int ret;

  if (show(opt, 4)) {
    output(opt, 4, _("Merging:"));
    output_commit_title(opt, h1);
    output_commit_title(opt, h2);
  }

  if (!merge_bases) {
    if (repo_get_merge_bases(the_repository, h1, h2,
           &merge_bases) < 0) {
      ret = -1;
      goto out;
    }
    merge_bases = reverse_commit_list(merge_bases);
  }

  if (show(opt, 5)) {
    unsigned cnt = commit_list_count(merge_bases);

    output(opt, 5, Q_("found %u common ancestor:",
        "found %u common ancestors:", cnt), cnt);
    for (iter = merge_bases; iter; iter = iter->next)
      output_commit_title(opt, iter->item);
  }

  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 (opt->ancestor && !opt->priv->call_depth) {
    ancestor_name = opt->ancestor;
  } else if (merge_bases) {
    ancestor_name = "merged common ancestors";
  } else {
    strbuf_add_unique_abbrev(&merge_base_abbrev,
           &merged_merge_bases->object.oid,
           DEFAULT_ABBREV);
    ancestor_name = merge_base_abbrev.buf;
  }

  for (iter = merge_bases; iter; iter = iter->next) {
    const char *saved_b1, *saved_b2;
    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.
     */
    discard_index(opt->repo->index);
    saved_b1 = opt->branch1;
    saved_b2 = opt->branch2;
    opt->branch1 = "Temporary merge branch 1";
    opt->branch2 = "Temporary merge branch 2";
    if (merge_recursive_internal(opt, merged_merge_bases, iter->item,
               NULL, &merged_merge_bases) < 0) {
      ret = -1;
      goto out;
    }
    opt->branch1 = saved_b1;
    opt->branch2 = saved_b2;
    opt->priv->call_depth--;

    if (!merged_merge_bases) {
      ret = err(opt, _("merge returned no commit"));
      goto out;
    }
  }

  /*
   * FIXME: Since merge_recursive_internal() is only ever called by
   * places that ensure the index is loaded first
   * (e.g. builtin/merge.c, rebase/sequencer, etc.), in the common
   * case where the merge base was unique that means when we get here
   * we immediately discard the index and re-read it, which is a
   * complete waste of time.  We should only be discarding and
   * re-reading if we were forced to recurse.
   */
  discard_index(opt->repo->index);
  if (!opt->priv->call_depth)
    repo_read_index(opt->repo);

  opt->ancestor = ancestor_name;
  ret = merge_trees_internal(opt,
           repo_get_commit_tree(opt->repo, h1),
           repo_get_commit_tree(opt->repo, h2),
           repo_get_commit_tree(opt->repo,
              merged_merge_bases),
           &result_tree);
  opt->ancestor = NULL;  /* avoid accidental re-use of opt->ancestor */
  if (ret < 0) {
    flush_output(opt);
    goto out;
  }

  if (opt->priv->call_depth) {
    *result = make_virtual_commit(opt->repo, result_tree,
                "merged tree");
    commit_list_insert(h1, &(*result)->parents);
    commit_list_insert(h2, &(*result)->parents->next);
  }

out:
  strbuf_release(&merge_base_abbrev);
  free_commit_list(merge_bases);
  return ret;
}

static int merge_start(struct merge_options *opt, struct tree *head)
{
  struct strbuf sb = STRBUF_INIT;

  /* Sanity checks on opt */
  assert(opt->repo);

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

  assert(opt->detect_renames >= -1 &&
         opt->detect_renames <= DIFF_DETECT_COPY);
  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);

  assert(opt->verbosity >= 0 && opt->verbosity <= 5);
  assert(opt->buffer_output <= 2);
  assert(opt->obuf.len == 0);

  assert(opt->priv == NULL);

  /* Not supported; option specific to merge-ort */
  assert(!opt->record_conflict_msgs_as_headers);
  assert(!opt->msg_header_prefix);

  /* Sanity check on repo state; index must match head */
  if (repo_index_has_changes(opt->repo, head, &sb)) {
    err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
        sb.buf);
    strbuf_release(&sb);
    return -1;
  }

  CALLOC_ARRAY(opt->priv, 1);
  string_list_init_dup(&opt->priv->df_conflict_file_set);
  return 0;
}

static void merge_finalize(struct merge_options *opt)
{
  flush_output(opt);
  if (!opt->priv->call_depth && opt->buffer_output < 2)
    strbuf_release(&opt->obuf);
  if (show(opt, 2))
    diff_warn_rename_limit("merge.renamelimit",
               opt->priv->needed_rename_limit, 0);
  hashmap_clear_and_free(&opt->priv->current_file_dir_set,
             struct path_hashmap_entry, e);
  string_list_clear(&opt->priv->df_conflict_file_set, 0);
  FREE_AND_NULL(opt->priv);
}

int merge_trees(struct merge_options *opt,
    struct tree *head,
    struct tree *merge,
    struct tree *merge_base)
{
  int clean;
  struct tree *ignored;

  assert(opt->ancestor != NULL);

  if (merge_start(opt, head))
    return -1;
  clean = merge_trees_internal(opt, head, merge, merge_base, &ignored);
  merge_finalize(opt);

  return clean;
}

int merge_recursive(struct merge_options *opt,
        struct commit *h1,
        struct commit *h2,
        const struct commit_list *merge_bases,
        struct commit **result)
{
  int clean;

  assert(opt->ancestor == NULL ||
         !strcmp(opt->ancestor, "constructed merge base"));

  prepare_repo_settings(opt->repo);
  opt->repo->settings.command_requires_full_index = 1;

  if (merge_start(opt, repo_get_commit_tree(opt->repo, h1)))
    return -1;
  clean = merge_recursive_internal(opt, h1, h2, merge_bases, result);
  merge_finalize(opt);

  return clean;
}

static struct commit *get_ref(struct repository *repo,
            const struct object_id *oid,
            const char *name)
{
  struct object *object;

  object = deref_tag(repo, parse_object(repo, oid),
         name, strlen(name));
  if (!object)
    return NULL;
  if (object->type == OBJ_TREE)
    return make_virtual_commit(repo, (struct tree*)object, name);
  if (object->type != OBJ_COMMIT)
    return NULL;
  if (repo_parse_commit(repo, (struct commit *)object))
    return NULL;
  return (struct commit *)object;
}

int merge_recursive_generic(struct merge_options *opt,
          const struct object_id *head,
          const struct object_id *merge,
          int num_merge_bases,
          const struct object_id *merge_bases,
          struct commit **result)
{
  int clean;
  struct lock_file lock = LOCK_INIT;
  struct commit *head_commit = get_ref(opt->repo, head, opt->branch1);
  struct commit *next_commit = get_ref(opt->repo, merge, opt->branch2);
  struct commit_list *ca = NULL;

  if (merge_bases) {
    int i;
    for (i = 0; i < num_merge_bases; ++i) {
      struct commit *base;
      if (!(base = get_ref(opt->repo, &merge_bases[i],
               oid_to_hex(&merge_bases[i]))))
        return err(opt, _("Could not parse object '%s'"),
             oid_to_hex(&merge_bases[i]));
      commit_list_insert(base, &ca);
    }
    if (num_merge_bases == 1)
      opt->ancestor = "constructed merge base";
  }

  repo_hold_locked_index(opt->repo, &lock, LOCK_DIE_ON_ERROR);
  clean = merge_recursive(opt, head_commit, next_commit, ca,
        result);
  free_commit_list(ca);
  if (clean < 0) {
    rollback_lock_file(&lock);
    return clean;
  }

  if (write_locked_index(opt->repo->index, &lock,
             COMMIT_LOCK | SKIP_IF_UNCHANGED))
    return err(opt, _("Unable to write index."));

  return clean ? 0 : 1;
}

static void merge_recursive_config(struct merge_options *opt, int ui)
{
  char *value = NULL;
  int renormalize = 0;
  git_config_get_int("merge.verbosity", &opt->verbosity);
  git_config_get_int("diff.renamelimit", &opt->rename_limit);
  git_config_get_int("merge.renamelimit", &opt->rename_limit);
  git_config_get_bool("merge.renormalize", &renormalize);
  opt->renormalize = renormalize;
  if (!git_config_get_string("diff.renames", &value)) {
    opt->detect_renames = git_config_rename("diff.renames", value);
    free(value);
  }
  if (!git_config_get_string("merge.renames", &value)) {
    opt->detect_renames = git_config_rename("merge.renames", value);
    free(value);
  }
  if (!git_config_get_string("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 (!git_config_get_string("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);
    }
  }
  git_config(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;

  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 */
    DIFF_XDL_CLR(opt, NEED_MINIMAL);
    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: 2024-09-16 06:12