/src/git/diffcore-rename.c

Source
/*
 *
 * Copyright (C) 2005 Junio C Hamano
 */

#include "git-compat-util.h"
#include "diff.h"
#include "diffcore.h"
#include "object-file.h"
#include "hashmap.h"
#include "mem-pool.h"
#include "oid-array.h"
#include "progress.h"
#include "promisor-remote.h"
#include "string-list.h"
#include "strmap.h"
#include "trace2.h"

/* Table of rename/copy destinations */

static struct diff_rename_dst {
  struct diff_filepair *p;
  struct diff_filespec *filespec_to_free;
  int is_rename; /* false -> just a create; true -> rename or copy */
} *rename_dst;
static int rename_dst_nr, rename_dst_alloc;
/* Mapping from break source pathname to break destination index */
static struct strintmap *break_idx = NULL;

static struct diff_rename_dst *locate_rename_dst(struct diff_filepair *p)
{
  /* Lookup by p->ONE->path */
  int idx = break_idx ? strintmap_get(break_idx, p->one->path) : -1;
  return (idx == -1 || idx == rename_dst_nr) ? NULL : &rename_dst[idx];
}

/*
 * Returns 0 on success, -1 if we found a duplicate.
 */
static int add_rename_dst(struct diff_filepair *p)
{
  ALLOC_GROW(rename_dst, rename_dst_nr + 1, rename_dst_alloc);
  rename_dst[rename_dst_nr].p = p;
  rename_dst[rename_dst_nr].filespec_to_free = NULL;
  rename_dst[rename_dst_nr].is_rename = 0;
  rename_dst_nr++;
  return 0;
}

/* Table of rename/copy src files */
static struct diff_rename_src {
  struct diff_filepair *p;
  unsigned short score; /* to remember the break score */
} *rename_src;
static int rename_src_nr, rename_src_alloc;

static void register_rename_src(struct diff_filepair *p)
{
  if (p->broken_pair) {
    if (!break_idx) {
      break_idx = xmalloc(sizeof(*break_idx));
      strintmap_init_with_options(break_idx, -1, NULL, 0);
    }
    strintmap_set(break_idx, p->one->path, rename_dst_nr);
  }

  ALLOC_GROW(rename_src, rename_src_nr + 1, rename_src_alloc);
  rename_src[rename_src_nr].p = p;
  rename_src[rename_src_nr].score = p->score;
  rename_src_nr++;
}

static int basename_same(struct diff_filespec *src, struct diff_filespec *dst)
{
  int src_len = strlen(src->path), dst_len = strlen(dst->path);
  while (src_len && dst_len) {
    char c1 = src->path[--src_len];
    char c2 = dst->path[--dst_len];
    if (c1 != c2)
      return 0;
    if (c1 == '/')
      return 1;
  }
  return (!src_len || src->path[src_len - 1] == '/') &&
    (!dst_len || dst->path[dst_len - 1] == '/');
}

struct diff_score {
  int src; /* index in rename_src */
  int dst; /* index in rename_dst */
  unsigned short score;
  short name_score;
};

struct inexact_prefetch_options {
  struct repository *repo;
  int skip_unmodified;
};
static void inexact_prefetch(void *prefetch_options)
{
  struct inexact_prefetch_options *options = prefetch_options;
  int i;
  struct oid_array to_fetch = OID_ARRAY_INIT;

  for (i = 0; i < rename_dst_nr; i++) {
    if (rename_dst[i].p->renamed_pair)
      /*
       * The loop in diffcore_rename() will not need these
       * blobs, so skip prefetching.
       */
      continue; /* already found exact match */
    diff_add_if_missing(options->repo, &to_fetch,
            rename_dst[i].p->two);
  }
  for (i = 0; i < rename_src_nr; i++) {
    if (options->skip_unmodified &&
        diff_unmodified_pair(rename_src[i].p))
      /*
       * The loop in diffcore_rename() will not need these
       * blobs, so skip prefetching.
       */
      continue;
    diff_add_if_missing(options->repo, &to_fetch,
            rename_src[i].p->one);
  }
  promisor_remote_get_direct(options->repo, to_fetch.oid, to_fetch.nr);
  oid_array_clear(&to_fetch);
}

static int estimate_similarity(struct repository *r,
             struct diff_filespec *src,
             struct diff_filespec *dst,
             int minimum_score,
             struct diff_populate_filespec_options *dpf_opt)
{
  /* src points at a file that existed in the original tree (or
   * optionally a file in the destination tree) and dst points
   * at a newly created file.  They may be quite similar, in which
   * case we want to say src is renamed to dst or src is copied into
   * dst, and then some edit has been applied to dst.
   *
   * Compare them and return how similar they are, representing
   * the score as an integer between 0 and MAX_SCORE.
   *
   * When there is an exact match, it is considered a better
   * match than anything else; the destination does not even
   * call into this function in that case.
   */
  unsigned long max_size, delta_size, base_size, src_copied, literal_added;
  int score;

  /* We deal only with regular files.  Symlink renames are handled
   * only when they are exact matches --- in other words, no edits
   * after renaming.
   */
  if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
    return 0;

  /*
   * Need to check that source and destination sizes are
   * filled in before comparing them.
   *
   * If we already have "cnt_data" filled in, we know it's
   * all good (avoid checking the size for zero, as that
   * is a possible size - we really should have a flag to
   * say whether the size is valid or not!)
   */
  dpf_opt->check_size_only = 1;

  if (!src->cnt_data &&
      diff_populate_filespec(r, src, dpf_opt))
    return 0;
  if (!dst->cnt_data &&
      diff_populate_filespec(r, dst, dpf_opt))
    return 0;

  max_size = ((src->size > dst->size) ? src->size : dst->size);
  base_size = ((src->size < dst->size) ? src->size : dst->size);
  delta_size = max_size - base_size;

  /* We would not consider edits that change the file size so
   * drastically.  delta_size must be smaller than
   * (MAX_SCORE-minimum_score)/MAX_SCORE * min(src->size, dst->size).
   *
   * Note that base_size == 0 case is handled here already
   * and the final score computation below would not have a
   * divide-by-zero issue.
   */
  if (max_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
    return 0;

  dpf_opt->check_size_only = 0;

  if (!src->cnt_data && diff_populate_filespec(r, src, dpf_opt))
    return 0;
  if (!dst->cnt_data && diff_populate_filespec(r, dst, dpf_opt))
    return 0;

  if (diffcore_count_changes(r, src, dst,
           &src->cnt_data, &dst->cnt_data,
           &src_copied, &literal_added))
    return 0;

  /* How similar are they?
   * what percentage of material in dst are from source?
   */
  if (!dst->size)
    score = 0; /* should not happen */
  else
    score = (int)(src_copied * MAX_SCORE / max_size);
  return score;
}

static void record_rename_pair(int dst_index, int src_index, int score)
{
  struct diff_filepair *src = rename_src[src_index].p;
  struct diff_filepair *dst = rename_dst[dst_index].p;

  if (dst->renamed_pair)
    die("internal error: dst already matched.");

  src->one->rename_used++;
  src->one->count++;

  rename_dst[dst_index].filespec_to_free = dst->one;
  rename_dst[dst_index].is_rename = 1;

  dst->one = src->one;
  dst->renamed_pair = 1;
  if (!strcmp(dst->one->path, dst->two->path))
    dst->score = rename_src[src_index].score;
  else
    dst->score = score;
}

/*
 * We sort the rename similarity matrix with the score, in descending
 * order (the most similar first).
 */
static int score_compare(const void *a_, const void *b_)
{
  const struct diff_score *a = a_, *b = b_;

  /* sink the unused ones to the bottom */
  if (a->dst < 0)
    return (0 <= b->dst);
  else if (b->dst < 0)
    return -1;

  if (a->score == b->score)
    return b->name_score - a->name_score;

  return b->score - a->score;
}

struct file_similarity {
  struct hashmap_entry entry;
  int index;
  struct diff_filespec *filespec;
};

static unsigned int hash_filespec(struct repository *r,
          struct diff_filespec *filespec)
{
  if (!filespec->oid_valid) {
    if (diff_populate_filespec(r, filespec, NULL))
      return 0;
    hash_object_file(r->hash_algo, filespec->data, filespec->size,
         OBJ_BLOB, &filespec->oid);
  }
  return oidhash(&filespec->oid);
}

static int find_identical_files(struct hashmap *srcs,
        int dst_index,
        struct diff_options *options)
{
  int renames = 0;
  struct diff_filespec *target = rename_dst[dst_index].p->two;
  struct file_similarity *p, *best = NULL;
  int i = 100, best_score = -1;
  unsigned int hash = hash_filespec(options->repo, target);

  /*
   * Find the best source match for specified destination.
   */
  p = hashmap_get_entry_from_hash(srcs, hash, NULL,
          struct file_similarity, entry);
  hashmap_for_each_entry_from(srcs, p, entry) {
    int score;
    struct diff_filespec *source = p->filespec;

    /* False hash collision? */
    if (!oideq(&source->oid, &target->oid))
      continue;
    /* Non-regular files? If so, the modes must match! */
    if (!S_ISREG(source->mode) || !S_ISREG(target->mode)) {
      if (source->mode != target->mode)
        continue;
    }
    /* Give higher scores to sources that haven't been used already */
    score = !source->rename_used;
    if (source->rename_used && options->detect_rename != DIFF_DETECT_COPY)
      continue;
    score += basename_same(source, target);
    if (score > best_score) {
      best = p;
      best_score = score;
      if (score == 2)
        break;
    }

    /* Too many identical alternatives? Pick one */
    if (!--i)
      break;
  }
  if (best) {
    record_rename_pair(dst_index, best->index, MAX_SCORE);
    renames++;
  }
  return renames;
}

static void insert_file_table(struct repository *r,
            struct mem_pool *pool,
            struct hashmap *table, int index,
            struct diff_filespec *filespec)
{
  struct file_similarity *entry = mem_pool_alloc(pool, sizeof(*entry));

  entry->index = index;
  entry->filespec = filespec;

  hashmap_entry_init(&entry->entry, hash_filespec(r, filespec));
  hashmap_add(table, &entry->entry);
}

/*
 * Find exact renames first.
 *
 * The first round matches up the up-to-date entries,
 * and then during the second round we try to match
 * cache-dirty entries as well.
 */
static int find_exact_renames(struct diff_options *options,
            struct mem_pool *pool)
{
  int i, renames = 0;
  struct hashmap file_table;

  /* Add all sources to the hash table in reverse order, because
   * later on they will be retrieved in LIFO order.
   */
  hashmap_init(&file_table, NULL, NULL, rename_src_nr);
  for (i = rename_src_nr-1; i >= 0; i--)
    insert_file_table(options->repo, pool,
          &file_table, i,
          rename_src[i].p->one);

  /* Walk the destinations and find best source match */
  for (i = 0; i < rename_dst_nr; i++)
    renames += find_identical_files(&file_table, i, options);

  /* Free the hash data structure (entries will be freed with the pool) */
  hashmap_clear(&file_table);

  return renames;
}

struct dir_rename_info {
  struct strintmap idx_map;
  struct strmap dir_rename_guess;
  struct strmap *dir_rename_count;
  struct strintmap *relevant_source_dirs;
  unsigned setup;
};

static char *get_dirname(const char *filename)
{
  const char *slash = strrchr(filename, '/');
  return slash ? xstrndup(filename, slash - filename) : xstrdup("");
}

static void dirname_munge(char *filename)
{
  char *slash = strrchr(filename, '/');
  if (!slash)
    slash = filename;
  *slash = '\0';
}

static const char *get_highest_rename_path(struct strintmap *counts)
{
  int highest_count = 0;
  const char *highest_destination_dir = NULL;
  struct hashmap_iter iter;
  struct strmap_entry *entry;

  strintmap_for_each_entry(counts, &iter, entry) {
    const char *destination_dir = entry->key;
    intptr_t count = (intptr_t)entry->value;
    if (count > highest_count) {
      highest_count = count;
      highest_destination_dir = destination_dir;
    }
  }
  return highest_destination_dir;
}

static const char *UNKNOWN_DIR = "/";  /* placeholder -- short, illegal directory */

static int dir_rename_already_determinable(struct strintmap *counts)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;
  int first = 0, second = 0, unknown = 0;
  strintmap_for_each_entry(counts, &iter, entry) {
    const char *destination_dir = entry->key;
    intptr_t count = (intptr_t)entry->value;
    if (!strcmp(destination_dir, UNKNOWN_DIR)) {
      unknown = count;
    } else if (count >= first) {
      second = first;
      first = count;
    } else if (count >= second) {
      second = count;
    }
  }
  return first > second + unknown;
}

static void increment_count(struct dir_rename_info *info,
          const char *old_dir,
          const char *new_dir)
{
  struct strintmap *counts;
  struct strmap_entry *e;

  /* Get the {new_dirs -> counts} mapping using old_dir */
  e = strmap_get_entry(info->dir_rename_count, old_dir);
  if (e) {
    counts = e->value;
  } else {
    counts = xmalloc(sizeof(*counts));
    strintmap_init_with_options(counts, 0, NULL, 1);
    strmap_put(info->dir_rename_count, old_dir, counts);
  }

  /* Increment the count for new_dir */
  strintmap_incr(counts, new_dir, 1);
}

static void update_dir_rename_counts(struct dir_rename_info *info,
             struct strintmap *dirs_removed,
             const char *oldname,
             const char *newname)
{
  char *old_dir;
  char *new_dir;
  const char new_dir_first_char = newname[0];
  int first_time_in_loop = 1;

  if (!info->setup)
    /*
     * info->setup is 0 here in two cases: (1) all auxiliary
     * vars (like dirs_removed) were NULL so
     * initialize_dir_rename_info() returned early, or (2)
     * either break detection or copy detection are active so
     * that we never called initialize_dir_rename_info().  In
     * the former case, we don't have enough info to know if
     * directories were renamed (because dirs_removed lets us
     * know about a necessary prerequisite, namely if they were
     * removed), and in the latter, we don't care about
     * directory renames or find_basename_matches.
     *
     * This matters because both basename and inexact matching
     * will also call update_dir_rename_counts().  In either of
     * the above two cases info->dir_rename_counts will not
     * have been properly initialized which prevents us from
     * updating it, but in these two cases we don't care about
     * dir_rename_counts anyway, so we can just exit early.
     */
    return;


  old_dir = xstrdup(oldname);
  new_dir = xstrdup(newname);

  while (1) {
    int drd_flag = NOT_RELEVANT;

    /* Get old_dir, skip if its directory isn't relevant. */
    dirname_munge(old_dir);
    if (info->relevant_source_dirs &&
        !strintmap_contains(info->relevant_source_dirs, old_dir))
      break;

    /* Get new_dir */
    dirname_munge(new_dir);

    /*
     * When renaming
     *   "a/b/c/d/e/foo.c" -> "a/b/some/thing/else/e/foo.c"
     * then this suggests that both
     *   a/b/c/d/e/ => a/b/some/thing/else/e/
     *   a/b/c/d/   => a/b/some/thing/else/
     * so we want to increment counters for both.  We do NOT,
     * however, also want to suggest that there was the following
     * rename:
     *   a/b/c/ => a/b/some/thing/
     * so we need to quit at that point.
     *
     * Note the when first_time_in_loop, we only strip off the
     * basename, and we don't care if that's different.
     */
    if (!first_time_in_loop) {
      char *old_sub_dir = strchr(old_dir, '\0')+1;
      char *new_sub_dir = strchr(new_dir, '\0')+1;
      if (!*new_dir) {
        /*
         * Special case when renaming to root directory,
         * i.e. when new_dir == "".  In this case, we had
         * something like
         *    a/b/subdir => subdir
         * and so dirname_munge() sets things up so that
         *    old_dir = "a/b\0subdir\0"
         *    new_dir = "\0ubdir\0"
         * We didn't have a '/' to overwrite a '\0' onto
         * in new_dir, so we have to compare differently.
         */
        if (new_dir_first_char != old_sub_dir[0] ||
            strcmp(old_sub_dir+1, new_sub_dir))
          break;
      } else {
        if (strcmp(old_sub_dir, new_sub_dir))
          break;
      }
    }

    /*
     * Above we suggested that we'd keep recording renames for
     * all ancestor directories where the trailing directories
     * matched, i.e. for
     *   "a/b/c/d/e/foo.c" -> "a/b/some/thing/else/e/foo.c"
     * we'd increment rename counts for each of
     *   a/b/c/d/e/ => a/b/some/thing/else/e/
     *   a/b/c/d/   => a/b/some/thing/else/
     * However, we only need the rename counts for directories
     * in dirs_removed whose value is RELEVANT_FOR_SELF.
     * However, we add one special case of also recording it for
     * first_time_in_loop because find_basename_matches() can
     * use that as a hint to find a good pairing.
     */
    if (dirs_removed)
      drd_flag = strintmap_get(dirs_removed, old_dir);
    if (drd_flag == RELEVANT_FOR_SELF || first_time_in_loop)
      increment_count(info, old_dir, new_dir);

    first_time_in_loop = 0;
    if (drd_flag == NOT_RELEVANT)
      break;
    /* If we hit toplevel directory ("") for old or new dir, quit */
    if (!*old_dir || !*new_dir)
      break;
  }

  /* Free resources we don't need anymore */
  free(old_dir);
  free(new_dir);
}

static void initialize_dir_rename_info(struct dir_rename_info *info,
               struct strintmap *relevant_sources,
               struct strintmap *dirs_removed,
               struct strmap *dir_rename_count,
               struct strmap *cached_pairs)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;
  int i;

  if (!dirs_removed && !relevant_sources) {
    info->setup = 0;
    return;
  }
  info->setup = 1;

  info->dir_rename_count = dir_rename_count;
  if (!info->dir_rename_count) {
    info->dir_rename_count = xmalloc(sizeof(*dir_rename_count));
    strmap_init(info->dir_rename_count);
  }
  strintmap_init_with_options(&info->idx_map, -1, NULL, 0);
  strmap_init_with_options(&info->dir_rename_guess, NULL, 0);

  /* Setup info->relevant_source_dirs */
  info->relevant_source_dirs = NULL;
  if (dirs_removed || !relevant_sources) {
    info->relevant_source_dirs = dirs_removed; /* might be NULL */
  } else {
    info->relevant_source_dirs = xmalloc(sizeof(struct strintmap));
    strintmap_init(info->relevant_source_dirs, 0 /* unused */);
    strintmap_for_each_entry(relevant_sources, &iter, entry) {
      char *dirname = get_dirname(entry->key);
      if (!dirs_removed ||
          strintmap_contains(dirs_removed, dirname))
        strintmap_set(info->relevant_source_dirs,
                dirname, 0 /* value irrelevant */);
      free(dirname);
    }
  }

  /*
   * Loop setting up both info->idx_map, and doing setup of
   * info->dir_rename_count.
   */
  for (i = 0; i < rename_dst_nr; ++i) {
    /*
     * For non-renamed files, make idx_map contain mapping of
     *   filename -> index (index within rename_dst, that is)
     */
    if (!rename_dst[i].is_rename) {
      char *filename = rename_dst[i].p->two->path;
      strintmap_set(&info->idx_map, filename, i);
      continue;
    }

    /*
     * For everything else (i.e. renamed files), make
     * dir_rename_count contain a map of a map:
     *   old_directory -> {new_directory -> count}
     * In other words, for every pair look at the directories for
     * the old filename and the new filename and count how many
     * times that pairing occurs.
     */
    update_dir_rename_counts(info, dirs_removed,
           rename_dst[i].p->one->path,
           rename_dst[i].p->two->path);
  }

  /* Add cached_pairs to counts */
  strmap_for_each_entry(cached_pairs, &iter, entry) {
    const char *old_name = entry->key;
    const char *new_name = entry->value;
    if (!new_name)
      /* known delete; ignore it */
      continue;

    update_dir_rename_counts(info, dirs_removed, old_name, new_name);
  }

  /*
   * Now we collapse
   *    dir_rename_count: old_directory -> {new_directory -> count}
   * down to
   *    dir_rename_guess: old_directory -> best_new_directory
   * where best_new_directory is the one with the highest count.
   */
  strmap_for_each_entry(info->dir_rename_count, &iter, entry) {
    /* entry->key is source_dir */
    struct strintmap *counts = entry->value;
    char *best_newdir;

    best_newdir = xstrdup(get_highest_rename_path(counts));
    strmap_put(&info->dir_rename_guess, entry->key,
         best_newdir);
  }
}

void partial_clear_dir_rename_count(struct strmap *dir_rename_count)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;

  strmap_for_each_entry(dir_rename_count, &iter, entry) {
    struct strintmap *counts = entry->value;
    strintmap_clear(counts);
  }
  strmap_partial_clear(dir_rename_count, 1);
}

static void cleanup_dir_rename_info(struct dir_rename_info *info,
            struct strintmap *dirs_removed,
            int keep_dir_rename_count)
{
  struct hashmap_iter iter;
  struct strmap_entry *entry;
  struct string_list to_remove = STRING_LIST_INIT_NODUP;

  if (!info->setup)
    return;

  /* idx_map */
  strintmap_clear(&info->idx_map);

  /* dir_rename_guess */
  strmap_clear(&info->dir_rename_guess, 1);

  /* relevant_source_dirs */
  if (info->relevant_source_dirs &&
      info->relevant_source_dirs != dirs_removed) {
    strintmap_clear(info->relevant_source_dirs);
    FREE_AND_NULL(info->relevant_source_dirs);
  }

  /* dir_rename_count */
  if (!keep_dir_rename_count) {
    partial_clear_dir_rename_count(info->dir_rename_count);
    strmap_clear(info->dir_rename_count, 1);
    FREE_AND_NULL(info->dir_rename_count);
    return;
  }

  /*
   * Although dir_rename_count was passed in
   * diffcore_rename_extended() and we want to keep it around and
   * return it to that caller, we first want to remove any counts in
   * the maps associated with UNKNOWN_DIR entries and any data
   * associated with directories that weren't renamed.
   */
  strmap_for_each_entry(info->dir_rename_count, &iter, entry) {
    const char *source_dir = entry->key;
    struct strintmap *counts = entry->value;

    if (!strintmap_get(dirs_removed, source_dir)) {
      string_list_append(&to_remove, source_dir);
      strintmap_clear(counts);
      continue;
    }

    if (strintmap_contains(counts, UNKNOWN_DIR))
      strintmap_remove(counts, UNKNOWN_DIR);
  }
  for (size_t i = 0; i < to_remove.nr; ++i)
    strmap_remove(info->dir_rename_count,
            to_remove.items[i].string, 1);
  string_list_clear(&to_remove, 0);
}

static const char *get_basename(const char *filename)
{
  /*
   * gitbasename() has to worry about special drives, multiple
   * directory separator characters, trailing slashes, NULL or
   * empty strings, etc.  We only work on filenames as stored in
   * git, and thus get to ignore all those complications.
   */
  const char *base = strrchr(filename, '/');
  return base ? base + 1 : filename;
}

static int idx_possible_rename(char *filename, struct dir_rename_info *info)
{
  /*
   * Our comparison of files with the same basename (see
   * find_basename_matches() below), is only helpful when after exact
   * rename detection we have exactly one file with a given basename
   * among the rename sources and also only exactly one file with
   * that basename among the rename destinations.  When we have
   * multiple files with the same basename in either set, we do not
   * know which to compare against.  However, there are some
   * filenames that occur in large numbers (particularly
   * build-related filenames such as 'Makefile', '.gitignore', or
   * 'build.gradle' that potentially exist within every single
   * subdirectory), and for performance we want to be able to quickly
   * find renames for these files too.
   *
   * The reason basename comparisons are a useful heuristic was that it
   * is common for people to move files across directories while keeping
   * their filename the same.  If we had a way of determining or even
   * making a good educated guess about which directory these non-unique
   * basename files had moved the file to, we could check it.
   * Luckily...
   *
   * When an entire directory is in fact renamed, we have two factors
   * helping us out:
   *   (a) the original directory disappeared giving us a hint
   *       about when we can apply an extra heuristic.
   *   (a) we often have several files within that directory and
   *       subdirectories that are renamed without changes
   * So, rules for a heuristic:
   *   (0) If there basename matches are non-unique (the condition under
   *       which this function is called) AND
   *   (1) the directory in which the file was found has disappeared
   *       (i.e. dirs_removed is non-NULL and has a relevant entry) THEN
   *   (2) use exact renames of files within the directory to determine
   *       where the directory is likely to have been renamed to.  IF
   *       there is at least one exact rename from within that
   *       directory, we can proceed.
   *   (3) If there are multiple places the directory could have been
   *       renamed to based on exact renames, ignore all but one of them.
   *       Just use the destination with the most renames going to it.
   *   (4) Check if applying that directory rename to the original file
   *       would result in a destination filename that is in the
   *       potential rename set.  If so, return the index of the
   *       destination file (the index within rename_dst).
   *   (5) Compare the original file and returned destination for
   *       similarity, and if they are sufficiently similar, record the
   *       rename.
   *
   * This function, idx_possible_rename(), is only responsible for (4).
   * The conditions/steps in (1)-(3) are handled via setting up
   * dir_rename_count and dir_rename_guess in
   * initialize_dir_rename_info().  Steps (0) and (5) are handled by
   * the caller of this function.
   */
  char *old_dir, *new_dir;
  struct strbuf new_path = STRBUF_INIT;
  int idx;

  if (!info->setup)
    return -1;

  old_dir = get_dirname(filename);
  new_dir = strmap_get(&info->dir_rename_guess, old_dir);
  free(old_dir);
  if (!new_dir)
    return -1;

  strbuf_addstr(&new_path, new_dir);
  strbuf_addch(&new_path, '/');
  strbuf_addstr(&new_path, get_basename(filename));

  idx = strintmap_get(&info->idx_map, new_path.buf);
  strbuf_release(&new_path);
  return idx;
}

struct basename_prefetch_options {
  struct repository *repo;
  struct strintmap *relevant_sources;
  struct strintmap *sources;
  struct strintmap *dests;
  struct dir_rename_info *info;
};
static void basename_prefetch(void *prefetch_options)
{
  struct basename_prefetch_options *options = prefetch_options;
  struct strintmap *relevant_sources = options->relevant_sources;
  struct strintmap *sources = options->sources;
  struct strintmap *dests = options->dests;
  struct dir_rename_info *info = options->info;
  int i;
  struct oid_array to_fetch = OID_ARRAY_INIT;

  /*
   * TODO: The following loops mirror the code/logic from
   * find_basename_matches(), though not quite exactly.  Maybe
   * abstract the iteration logic out somehow?
   */
  for (i = 0; i < rename_src_nr; ++i) {
    char *filename = rename_src[i].p->one->path;
    const char *base = NULL;
    intptr_t src_index;
    intptr_t dst_index;

    /* Skip irrelevant sources */
    if (relevant_sources &&
        !strintmap_contains(relevant_sources, filename))
      continue;

    /*
     * If the basename is unique among remaining sources, then
     * src_index will equal 'i' and we can attempt to match it
     * to a unique basename in the destinations.  Otherwise,
     * use directory rename heuristics, if possible.
     */
    base = get_basename(filename);
    src_index = strintmap_get(sources, base);
    assert(src_index == -1 || src_index == i);

    if (strintmap_contains(dests, base)) {
      struct diff_filespec *one, *two;

      /* Find a matching destination, if possible */
      dst_index = strintmap_get(dests, base);
      if (src_index == -1 || dst_index == -1) {
        src_index = i;
        dst_index = idx_possible_rename(filename, info);
      }
      if (dst_index == -1)
        continue;

      /* Ignore this dest if already used in a rename */
      if (rename_dst[dst_index].is_rename)
        continue; /* already used previously */

      one = rename_src[src_index].p->one;
      two = rename_dst[dst_index].p->two;

      /* Add the pairs */
      diff_add_if_missing(options->repo, &to_fetch, two);
      diff_add_if_missing(options->repo, &to_fetch, one);
    }
  }

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

static int find_basename_matches(struct diff_options *options,
         int minimum_score,
         struct dir_rename_info *info,
         struct strintmap *relevant_sources,
         struct strintmap *dirs_removed)
{
  /*
   * When I checked in early 2020, over 76% of file renames in linux
   * just moved files to a different directory but kept the same
   * basename.  gcc did that with over 64% of renames, gecko did it
   * with over 79%, and WebKit did it with over 89%.
   *
   * Therefore we can bypass the normal exhaustive NxM matrix
   * comparison of similarities between all potential rename sources
   * and destinations by instead using file basename as a hint (i.e.
   * the portion of the filename after the last '/'), checking for
   * similarity between files with the same basename, and if we find
   * a pair that are sufficiently similar, record the rename pair and
   * exclude those two from the NxM matrix.
   *
   * This *might* cause us to find a less than optimal pairing (if
   * there is another file that we are even more similar to but has a
   * different basename).  Given the huge performance advantage
   * basename matching provides, and given the frequency with which
   * people use the same basename in real world projects, that's a
   * trade-off we are willing to accept when doing just rename
   * detection.
   *
   * If someone wants copy detection that implies they are willing to
   * spend more cycles to find similarities between files, so it may
   * be less likely that this heuristic is wanted.  If someone is
   * doing break detection, that means they do not want filename
   * similarity to imply any form of content similarity, and thus
   * this heuristic would definitely be incompatible.
   */

  int i, renames = 0;
  struct strintmap sources;
  struct strintmap dests;
  struct diff_populate_filespec_options dpf_options = {
    .check_binary = 0,
    .missing_object_cb = NULL,
    .missing_object_data = NULL
  };
  struct basename_prefetch_options prefetch_options = {
    .repo = options->repo,
    .relevant_sources = relevant_sources,
    .sources = &sources,
    .dests = &dests,
    .info = info
  };

  /*
   * Create maps of basename -> fullname(s) for remaining sources and
   * dests.
   */
  strintmap_init_with_options(&sources, -1, NULL, 0);
  strintmap_init_with_options(&dests, -1, NULL, 0);
  for (i = 0; i < rename_src_nr; ++i) {
    char *filename = rename_src[i].p->one->path;
    const char *base;

    /* exact renames removed in remove_unneeded_paths_from_src() */
    assert(!rename_src[i].p->one->rename_used);

    /* Record index within rename_src (i) if basename is unique */
    base = get_basename(filename);
    if (strintmap_contains(&sources, base))
      strintmap_set(&sources, base, -1);
    else
      strintmap_set(&sources, base, i);
  }
  for (i = 0; i < rename_dst_nr; ++i) {
    char *filename = rename_dst[i].p->two->path;
    const char *base;

    if (rename_dst[i].is_rename)
      continue; /* involved in exact match already. */

    /* Record index within rename_dst (i) if basename is unique */
    base = get_basename(filename);
    if (strintmap_contains(&dests, base))
      strintmap_set(&dests, base, -1);
    else
      strintmap_set(&dests, base, i);
  }

  if (repo_has_promisor_remote(options->repo)) {
    dpf_options.missing_object_cb = basename_prefetch;
    dpf_options.missing_object_data = &prefetch_options;
  }

  /* Now look for basename matchups and do similarity estimation */
  for (i = 0; i < rename_src_nr; ++i) {
    char *filename = rename_src[i].p->one->path;
    const char *base = NULL;
    intptr_t src_index;
    intptr_t dst_index;

    /* Skip irrelevant sources */
    if (relevant_sources &&
        !strintmap_contains(relevant_sources, filename))
      continue;

    /*
     * If the basename is unique among remaining sources, then
     * src_index will equal 'i' and we can attempt to match it
     * to a unique basename in the destinations.  Otherwise,
     * use directory rename heuristics, if possible.
     */
    base = get_basename(filename);
    src_index = strintmap_get(&sources, base);
    assert(src_index == -1 || src_index == i);

    if (strintmap_contains(&dests, base)) {
      struct diff_filespec *one, *two;
      int score;

      /* Find a matching destination, if possible */
      dst_index = strintmap_get(&dests, base);
      if (src_index == -1 || dst_index == -1) {
        src_index = i;
        dst_index = idx_possible_rename(filename, info);
      }
      if (dst_index == -1)
        continue;

      /* Ignore this dest if already used in a rename */
      if (rename_dst[dst_index].is_rename)
        continue; /* already used previously */

      /* Estimate the similarity */
      one = rename_src[src_index].p->one;
      two = rename_dst[dst_index].p->two;
      score = estimate_similarity(options->repo, one, two,
                minimum_score, &dpf_options);

      /* If sufficiently similar, record as rename pair */
      if (score < minimum_score)
        continue;
      record_rename_pair(dst_index, src_index, score);
      renames++;
      update_dir_rename_counts(info, dirs_removed,
             one->path, two->path);

      /*
       * Found a rename so don't need text anymore; if we
       * didn't find a rename, the filespec_blob would get
       * re-used when doing the matrix of comparisons.
       */
      diff_free_filespec_blob(one);
      diff_free_filespec_blob(two);
    }
  }

  strintmap_clear(&sources);
  strintmap_clear(&dests);

  return renames;
}

#define NUM_CANDIDATE_PER_DST 4
static void record_if_better(struct diff_score m[], struct diff_score *o)
{
  int i, worst;

  /* find the worst one */
  worst = 0;
  for (i = 1; i < NUM_CANDIDATE_PER_DST; i++)
    if (score_compare(&m[i], &m[worst]) > 0)
      worst = i;

  /* is it better than the worst one? */
  if (score_compare(&m[worst], o) > 0)
    m[worst] = *o;
}

/*
 * Returns:
 * 0 if we are under the limit;
 * 1 if we need to disable inexact rename detection;
 * 2 if we would be under the limit if we were given -C instead of -C -C.
 */
static int too_many_rename_candidates(int num_destinations, int num_sources,
              struct diff_options *options)
{
  int rename_limit = options->rename_limit;
  int i, limited_sources;

  options->needed_rename_limit = 0;

  /*
   * This basically does a test for the rename matrix not
   * growing larger than a "rename_limit" square matrix, ie:
   *
   *    num_destinations * num_sources > rename_limit * rename_limit
   *
   * We use st_mult() to check overflow conditions; in the
   * exceptional circumstance that size_t isn't large enough to hold
   * the multiplication, the system won't be able to allocate enough
   * memory for the matrix anyway.
   */
  if (rename_limit <= 0)
    return 0; /* treat as unlimited */
  if (st_mult(num_destinations, num_sources)
      <= st_mult(rename_limit, rename_limit))
    return 0;

  options->needed_rename_limit =
    num_sources > num_destinations ? num_sources : num_destinations;

  /* Are we running under -C -C? */
  if (!options->flags.find_copies_harder)
    return 1;

  /* Would we bust the limit if we were running under -C? */
  for (limited_sources = i = 0; i < num_sources; i++) {
    if (diff_unmodified_pair(rename_src[i].p))
      continue;
    limited_sources++;
  }
  if (st_mult(num_destinations, limited_sources)
      <= st_mult(rename_limit, rename_limit))
    return 2;
  return 1;
}

static int find_renames(struct diff_score *mx,
      int dst_cnt,
      int minimum_score,
      int copies,
      struct dir_rename_info *info,
      struct strintmap *dirs_removed)
{
  int count = 0, i;

  for (i = 0; i < dst_cnt * NUM_CANDIDATE_PER_DST; i++) {
    struct diff_rename_dst *dst;

    if ((mx[i].dst < 0) ||
        (mx[i].score < minimum_score))
      break; /* there is no more usable pair. */
    dst = &rename_dst[mx[i].dst];
    if (dst->is_rename)
      continue; /* already done, either exact or fuzzy. */
    if (!copies && rename_src[mx[i].src].p->one->rename_used)
      continue;
    record_rename_pair(mx[i].dst, mx[i].src, mx[i].score);
    count++;
    update_dir_rename_counts(info, dirs_removed,
           rename_src[mx[i].src].p->one->path,
           rename_dst[mx[i].dst].p->two->path);
  }
  return count;
}

static void remove_unneeded_paths_from_src(int detecting_copies,
             struct strintmap *interesting)
{
  int i, new_num_src;

  if (detecting_copies && !interesting)
    return; /* nothing to remove */
  if (break_idx)
    return; /* culling incompatible with break detection */

  /*
   * Note on reasons why we cull unneeded sources but not destinations:
   *   1) Pairings are stored in rename_dst (not rename_src), which we
   *      need to keep around.  So, we just can't cull rename_dst even
   *      if we wanted to.  But doing so wouldn't help because...
   *
   *   2) There is a matrix pairwise comparison that follows the
   *      "Performing inexact rename detection" progress message.
   *      Iterating over the destinations is done in the outer loop,
   *      hence we only iterate over each of those once and we can
   *      easily skip the outer loop early if the destination isn't
   *      relevant.  That's only one check per destination path to
   *      skip.
   *
   *      By contrast, the sources are iterated in the inner loop; if
   *      we check whether a source can be skipped, then we'll be
   *      checking it N separate times, once for each destination.
   *      We don't want to have to iterate over known-not-needed
   *      sources N times each, so avoid that by removing the sources
   *      from rename_src here.
   */
  for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
    struct diff_filespec *one = rename_src[i].p->one;

    /*
     * renames are stored in rename_dst, so if a rename has
     * already been detected using this source, we can just
     * remove the source knowing rename_dst has its info.
     */
    if (!detecting_copies && one->rename_used)
      continue;

    /* If we don't care about the source path, skip it */
    if (interesting && !strintmap_contains(interesting, one->path))
      continue;

    if (new_num_src < i)
      memcpy(&rename_src[new_num_src], &rename_src[i],
             sizeof(struct diff_rename_src));
    new_num_src++;
  }

  rename_src_nr = new_num_src;
}

static void handle_early_known_dir_renames(struct dir_rename_info *info,
             struct strintmap *relevant_sources,
             struct strintmap *dirs_removed)
{
  /*
   * Directory renames are determined via an aggregate of all renames
   * under them and using a "majority wins" rule.  The fact that
   * "majority wins", though, means we don't need all the renames
   * under the given directory, we only need enough to ensure we have
   * a majority.
   */

  int i, new_num_src;
  struct hashmap_iter iter;
  struct strmap_entry *entry;

  if (!dirs_removed || !relevant_sources)
    return; /* nothing to cull */
  if (break_idx)
    return; /* culling incompatbile with break detection */

  /*
   * Supplement dir_rename_count with number of potential renames,
   * marking all potential rename sources as mapping to UNKNOWN_DIR.
   */
  for (i = 0; i < rename_src_nr; i++) {
    char *old_dir;
    struct diff_filespec *one = rename_src[i].p->one;

    /*
     * sources that are part of a rename will have already been
     * removed by a prior call to remove_unneeded_paths_from_src()
     */
    assert(!one->rename_used);

    old_dir = get_dirname(one->path);
    while (*old_dir != '\0' &&
           NOT_RELEVANT != strintmap_get(dirs_removed, old_dir)) {
      char *freeme = old_dir;

      increment_count(info, old_dir, UNKNOWN_DIR);
      old_dir = get_dirname(old_dir);

      /* Free resources we don't need anymore */
      free(freeme);
    }
    /*
     * old_dir and new_dir free'd in increment_count, but
     * get_dirname() gives us a new pointer we need to free for
     * old_dir.  Also, if the loop runs 0 times we need old_dir
     * to be freed.
     */
    free(old_dir);
  }

  /*
   * For any directory which we need a potential rename detected for
   * (i.e. those marked as RELEVANT_FOR_SELF in dirs_removed), check
   * whether we have enough renames to satisfy the "majority rules"
   * requirement such that detecting any more renames of files under
   * it won't change the result.  For any such directory, mark that
   * we no longer need to detect a rename for it.  However, since we
   * might need to still detect renames for an ancestor of that
   * directory, use RELEVANT_FOR_ANCESTOR.
   */
  strmap_for_each_entry(info->dir_rename_count, &iter, entry) {
    /* entry->key is source_dir */
    struct strintmap *counts = entry->value;

    if (strintmap_get(dirs_removed, entry->key) ==
        RELEVANT_FOR_SELF &&
        dir_rename_already_determinable(counts)) {
      strintmap_set(dirs_removed, entry->key,
              RELEVANT_FOR_ANCESTOR);
    }
  }

  for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
    struct diff_filespec *one = rename_src[i].p->one;
    int val;

    val = strintmap_get(relevant_sources, one->path);

    /*
     * sources that were not found in relevant_sources should
     * have already been removed by a prior call to
     * remove_unneeded_paths_from_src()
     */
    assert(val != -1);

    if (val == RELEVANT_LOCATION) {
      int removable = 1;
      char *dir = get_dirname(one->path);
      while (1) {
        char *freeme = dir;
        int res = strintmap_get(dirs_removed, dir);

        /* Quit if not found or irrelevant */
        if (res == NOT_RELEVANT)
          break;
        /* If RELEVANT_FOR_SELF, can't remove */
        if (res == RELEVANT_FOR_SELF) {
          removable = 0;
          break;
        }
        /* Else continue searching upwards */
        assert(res == RELEVANT_FOR_ANCESTOR);
        dir = get_dirname(dir);
        free(freeme);
      }
      free(dir);
      if (removable) {
        strintmap_set(relevant_sources, one->path,
                RELEVANT_NO_MORE);
        continue;
      }
    }

    if (new_num_src < i)
      memcpy(&rename_src[new_num_src], &rename_src[i],
             sizeof(struct diff_rename_src));
    new_num_src++;
  }

  rename_src_nr = new_num_src;
}

static void free_filespec_data(struct diff_filespec *spec)
{
  if (!--spec->count)
    diff_free_filespec_data(spec);
}

static void pool_free_filespec(struct mem_pool *pool,
             struct diff_filespec *spec)
{
  if (!pool) {
    free_filespec(spec);
    return;
  }

  /*
   * Similar to free_filespec(), but only frees the data.  The spec
   * itself was allocated in the pool and should not be individually
   * freed.
   */
  free_filespec_data(spec);
}

void pool_diff_free_filepair(struct mem_pool *pool,
           struct diff_filepair *p)
{
  if (!pool) {
    diff_free_filepair(p);
    return;
  }

  /*
   * Similar to diff_free_filepair() but only frees the data from the
   * filespecs; not the filespecs or the filepair which were
   * allocated from the pool.
   */
  free_filespec_data(p->one);
  free_filespec_data(p->two);
}

void diffcore_rename_extended(struct diff_options *options,
            struct mem_pool *pool,
            struct strintmap *relevant_sources,
            struct strintmap *dirs_removed,
            struct strmap *dir_rename_count,
            struct strmap *cached_pairs)
{
  int detect_rename = options->detect_rename;
  int minimum_score = options->rename_score;
  struct diff_queue_struct *q = &diff_queued_diff;
  struct diff_queue_struct outq = DIFF_QUEUE_INIT;
  struct diff_score *mx;
  int i, j, rename_count, skip_unmodified = 0;
  int num_destinations, dst_cnt;
  int num_sources, want_copies;
  struct progress *progress = NULL;
  struct mem_pool local_pool;
  struct dir_rename_info info;
  struct diff_populate_filespec_options dpf_options = {
    .check_binary = 0,
    .missing_object_cb = NULL,
    .missing_object_data = NULL
  };
  struct inexact_prefetch_options prefetch_options = {
    .repo = options->repo
  };

  trace2_region_enter("diff", "setup", options->repo);
  info.setup = 0;
  ASSERT(!dir_rename_count || strmap_empty(dir_rename_count));
  want_copies = (detect_rename == DIFF_DETECT_COPY);
  if (dirs_removed && (break_idx || want_copies))
    BUG("dirs_removed incompatible with break/copy detection");
  if (break_idx && relevant_sources)
    BUG("break detection incompatible with source specification");
  if (!minimum_score)
    minimum_score = DEFAULT_RENAME_SCORE;

  for (i = 0; i < q->nr; i++) {
    struct diff_filepair *p = q->queue[i];
    if (!DIFF_FILE_VALID(p->one)) {
      if (!DIFF_FILE_VALID(p->two))
        continue; /* unmerged */
      else if (options->single_follow &&
         strcmp(options->single_follow, p->two->path))
        continue; /* not interested */
      else if (!options->flags.rename_empty &&
         is_empty_blob_oid(&p->two->oid,
               options->repo->hash_algo))
        continue;
      else if (add_rename_dst(p) < 0) {
        warning("skipping rename detection, detected"
          " duplicate destination '%s'",
          p->two->path);
        goto cleanup;
      }
    }
    else if (!options->flags.rename_empty &&
       is_empty_blob_oid(&p->one->oid,
             options->repo->hash_algo))
      continue;
    else if (!DIFF_PAIR_UNMERGED(p) && !DIFF_FILE_VALID(p->two)) {
      /*
       * If the source is a broken "delete", and
       * they did not really want to get broken,
       * that means the source actually stays.
       * So we increment the "rename_used" score
       * by one, to indicate ourselves as a user
       */
      if (p->broken_pair && !p->score)
        p->one->rename_used++;
      register_rename_src(p);
    }
    else if (want_copies) {
      /*
       * Increment the "rename_used" score by
       * one, to indicate ourselves as a user.
       */
      p->one->rename_used++;
      register_rename_src(p);
    }
  }
  trace2_region_leave("diff", "setup", options->repo);
  if (rename_dst_nr == 0 || rename_src_nr == 0)
    goto cleanup; /* nothing to do */

  trace2_region_enter("diff", "exact renames", options->repo);
  mem_pool_init(&local_pool, 32*1024);
  /*
   * We really want to cull the candidates list early
   * with cheap tests in order to avoid doing deltas.
   */
  rename_count = find_exact_renames(options, &local_pool);
  /*
   * Discard local_pool immediately instead of at "cleanup:" in order
   * to reduce maximum memory usage; inexact rename detection uses up
   * a fair amount of memory, and mem_pools can too.
   */
  mem_pool_discard(&local_pool, 0);
  trace2_region_leave("diff", "exact renames", options->repo);

  /* Did we only want exact renames? */
  if (minimum_score == MAX_SCORE)
    goto cleanup;

  num_sources = rename_src_nr;

  if (want_copies || break_idx) {
    /*
     * Cull sources:
     *   - remove ones corresponding to exact renames
     *   - remove ones not found in relevant_sources
     */
    trace2_region_enter("diff", "cull after exact", options->repo);
    remove_unneeded_paths_from_src(want_copies, relevant_sources);
    trace2_region_leave("diff", "cull after exact", options->repo);
  } else {
    /* Determine minimum score to match basenames */
    double factor = 0.5;
    char *basename_factor = getenv("GIT_BASENAME_FACTOR");
    int min_basename_score;

    if (basename_factor)
      factor = strtol(basename_factor, NULL, 10)/100.0;
    assert(factor >= 0.0 && factor <= 1.0);
    min_basename_score = minimum_score +
      (int)(factor * (MAX_SCORE - minimum_score));

    /*
     * Cull sources:
     *   - remove ones involved in renames (found via exact match)
     */
    trace2_region_enter("diff", "cull after exact", options->repo);
    remove_unneeded_paths_from_src(want_copies, NULL);
    trace2_region_leave("diff", "cull after exact", options->repo);

    /* Preparation for basename-driven matching. */
    trace2_region_enter("diff", "dir rename setup", options->repo);
    initialize_dir_rename_info(&info, relevant_sources,
             dirs_removed, dir_rename_count,
             cached_pairs);
    trace2_region_leave("diff", "dir rename setup", options->repo);

    /* Utilize file basenames to quickly find renames. */
    trace2_region_enter("diff", "basename matches", options->repo);
    rename_count += find_basename_matches(options,
                  min_basename_score,
                  &info,
                  relevant_sources,
                  dirs_removed);
    trace2_region_leave("diff", "basename matches", options->repo);

    /*
     * Cull sources, again:
     *   - remove ones involved in renames (found via basenames)
     *   - remove ones not found in relevant_sources
     * and
     *   - remove ones in relevant_sources which are needed only
     *     for directory renames IF no ancestry directory
     *     actually needs to know any more individual path
     *     renames under them
     */
    trace2_region_enter("diff", "cull basename", options->repo);
    remove_unneeded_paths_from_src(want_copies, relevant_sources);
    handle_early_known_dir_renames(&info, relevant_sources,
                 dirs_removed);
    trace2_region_leave("diff", "cull basename", options->repo);
  }

  /* Calculate how many rename destinations are left */
  num_destinations = (rename_dst_nr - rename_count);
  num_sources = rename_src_nr; /* rename_src_nr reflects lower number */

  /* All done? */
  if (!num_destinations || !num_sources)
    goto cleanup;

  switch (too_many_rename_candidates(num_destinations, num_sources,
             options)) {
  case 1:
    goto cleanup;
  case 2:
    options->degraded_cc_to_c = 1;
    skip_unmodified = 1;
    break;
  default:
    break;
  }

  trace2_region_enter("diff", "inexact renames", options->repo);
  if (options->show_rename_progress) {
    progress = start_delayed_progress(
        options->repo,
        _("Performing inexact rename detection"),
        (uint64_t)num_destinations * (uint64_t)num_sources);
  }

  /* Finish setting up dpf_options */
  prefetch_options.skip_unmodified = skip_unmodified;
  if (repo_has_promisor_remote(options->repo)) {
    dpf_options.missing_object_cb = inexact_prefetch;
    dpf_options.missing_object_data = &prefetch_options;
  }

  CALLOC_ARRAY(mx, st_mult(NUM_CANDIDATE_PER_DST, num_destinations));
  for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
    struct diff_filespec *two = rename_dst[i].p->two;
    struct diff_score *m;

    if (rename_dst[i].is_rename)
      continue; /* exact or basename match already handled */

    m = &mx[dst_cnt * NUM_CANDIDATE_PER_DST];
    for (j = 0; j < NUM_CANDIDATE_PER_DST; j++)
      m[j].dst = -1;

    for (j = 0; j < rename_src_nr; j++) {
      struct diff_filespec *one = rename_src[j].p->one;
      struct diff_score this_src;

      assert(!one->rename_used || want_copies || break_idx);

      if (skip_unmodified &&
          diff_unmodified_pair(rename_src[j].p))
        continue;

      this_src.score = estimate_similarity(options->repo,
                   one, two,
                   minimum_score,
                   &dpf_options);
      this_src.name_score = basename_same(one, two);
      this_src.dst = i;
      this_src.src = j;
      record_if_better(m, &this_src);
      /*
       * Once we run estimate_similarity,
       * We do not need the text anymore.
       */
      diff_free_filespec_blob(one);
      diff_free_filespec_blob(two);
    }
    dst_cnt++;
    display_progress(progress,
         (uint64_t)dst_cnt * (uint64_t)num_sources);
  }
  stop_progress(&progress);

  /* cost matrix sorted by most to least similar pair */
  STABLE_QSORT(mx, dst_cnt * NUM_CANDIDATE_PER_DST, score_compare);

  rename_count += find_renames(mx, dst_cnt, minimum_score, 0,
             &info, dirs_removed);
  if (want_copies)
    rename_count += find_renames(mx, dst_cnt, minimum_score, 1,
               &info, dirs_removed);
  free(mx);
  trace2_region_leave("diff", "inexact renames", options->repo);

 cleanup:
  /* At this point, we have found some renames and copies and they
   * are recorded in rename_dst.  The original list is still in *q.
   */
  trace2_region_enter("diff", "write back to queue", options->repo);
  for (i = 0; i < q->nr; i++) {
    struct diff_filepair *p = q->queue[i];
    struct diff_filepair *pair_to_free = NULL;

    if (DIFF_PAIR_UNMERGED(p)) {
      diff_q(&outq, p);
    }
    else if (!DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two)) {
      /* Creation */
      diff_q(&outq, p);
    }
    else if (DIFF_FILE_VALID(p->one) && !DIFF_FILE_VALID(p->two)) {
      /*
       * Deletion
       *
       * We would output this delete record if:
       *
       * (1) this is a broken delete and the counterpart
       *     broken create remains in the output; or
       * (2) this is not a broken delete, and rename_dst
       *     does not have a rename/copy to move p->one->path
       *     out of existence.
       *
       * Otherwise, the counterpart broken create
       * has been turned into a rename-edit; or
       * delete did not have a matching create to
       * begin with.
       */
      if (DIFF_PAIR_BROKEN(p)) {
        /* broken delete */
        struct diff_rename_dst *dst = locate_rename_dst(p);
        if (options->single_follow && dst &&
            strcmp(dst->p->two->path, p->two->path))
          dst = NULL;
        if (dst && dst->is_rename)
          /* counterpart is now rename/copy */
          pair_to_free = p;
      }
      else {
        if (p->one->rename_used)
          /* this path remains */
          pair_to_free = p;
      }

      if (!pair_to_free)
        diff_q(&outq, p);
    }
    else if (!diff_unmodified_pair(p))
      /* all the usual ones need to be kept */
      diff_q(&outq, p);
    else
      /* no need to keep unmodified pairs */
      pair_to_free = p;

    if (pair_to_free)
      pool_diff_free_filepair(pool, pair_to_free);
  }
  diff_debug_queue("done copying original", &outq);

  free(q->queue);
  *q = outq;
  diff_debug_queue("done collapsing", q);

  for (i = 0; i < rename_dst_nr; i++)
    if (rename_dst[i].filespec_to_free)
      pool_free_filespec(pool, rename_dst[i].filespec_to_free);

  cleanup_dir_rename_info(&info, dirs_removed, dir_rename_count != NULL);
  FREE_AND_NULL(rename_dst);
  rename_dst_nr = rename_dst_alloc = 0;
  FREE_AND_NULL(rename_src);
  rename_src_nr = rename_src_alloc = 0;
  if (break_idx) {
    strintmap_clear(break_idx);
    FREE_AND_NULL(break_idx);
  }
  trace2_region_leave("diff", "write back to queue", options->repo);
  return;
}

void diffcore_rename(struct diff_options *options)
{
  diffcore_rename_extended(options, NULL, NULL, NULL, NULL, NULL);
}

Coverage Report

Created: 2026-11-12 06:03