Subject: [PATCH 05/10] diffcore-rename: compute dir_rename_counts in stages

From: "Elijah Newren via GitGitGadget" <[email-masked]>
Date: Sun, 14 Feb 2021 07:58:58 +0000

From: Elijah Newren <[email-masked]>

We want to first compute dir_rename_counts based just on exact renames
to start, as that can provide us useful information in
find_basename_matches().  That will give us an incomplete result, which
we can then later augment as basename and inexact rename matches are
found.

Signed-off-by: Elijah Newren <[email-masked]>
---
 diffcore-rename.c | 76 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 62 insertions(+), 14 deletions(-)

diff --git a/diffcore-rename.c b/diffcore-rename.c
index aa21d4e7175c..489e9cb0871e 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -411,6 +411,28 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
 	char new_dir_first_char = new_dir[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;
+
 	while (1) {
 		dirname_munge(old_dir);
 		dirname_munge(new_dir);
@@ -471,14 +493,22 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
 	free(new_dir);
 }
 
-static void compute_dir_rename_counts(struct dir_rename_info *info,
-				      struct strset *dirs_removed,
-				      struct strmap *dir_rename_count)
+static void initialize_dir_rename_info(struct dir_rename_info *info,
+				       struct strset *dirs_removed,
+				       struct strmap *dir_rename_count)
 {
 	int i;
 
+	info->setup = 0;
+	if (!dirs_removed)
+		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);
+	}
 
 	for (i = 0; i < rename_dst_nr; ++i) {
 		/*
@@ -506,7 +536,6 @@ void partial_clear_dir_rename_count(struct strmap *dir_rename_count)
 	strmap_partial_clear(dir_rename_count, 1);
 }
 
-MAYBE_UNUSED
 static void cleanup_dir_rename_info(struct dir_rename_info *info,
 				    struct strset *dirs_removed,
 				    int keep_dir_rename_count)
@@ -561,7 +590,9 @@ static const char *get_basename(const char *filename)
 }
 
 static int find_basename_matches(struct diff_options *options,
-				 int minimum_score)
+				 int minimum_score,
+				 struct dir_rename_info *info,
+				 struct strset *dirs_removed)
 {
 	/*
 	 * When I checked in early 2020, over 76% of file renames in linux
@@ -669,6 +700,8 @@ static int find_basename_matches(struct diff_options *options,
 				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
@@ -752,7 +785,12 @@ static int too_many_rename_candidates(int num_destinations, int num_sources,
 	return 1;
 }
 
-static int find_renames(struct diff_score *mx, int dst_cnt, int minimum_score, int copies)
+static int find_renames(struct diff_score *mx,
+			int dst_cnt,
+			int minimum_score,
+			int copies,
+			struct dir_rename_info *info,
+			struct strset *dirs_removed)
 {
 	int count = 0, i;
 
@@ -769,6 +807,9 @@ static int find_renames(struct diff_score *mx, int dst_cnt, int minimum_score, i
 			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;
 }
@@ -840,6 +881,8 @@ void diffcore_rename_extended(struct diff_options *options,
 	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 (!minimum_score)
 		minimum_score = DEFAULT_RENAME_SCORE;
 
@@ -931,10 +974,17 @@ void diffcore_rename_extended(struct diff_options *options,
 		remove_unneeded_paths_from_src(want_copies);
 		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,
+					   dirs_removed, dir_rename_count);
+		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);
+						      min_basename_score,
+						      &info, dirs_removed);
 		trace2_region_leave("diff", "basename matches", options->repo);
 
 		/*
@@ -1020,18 +1070,15 @@ void diffcore_rename_extended(struct diff_options *options,
 	/* 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);
+	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);
+		rename_count += find_renames(mx, dst_cnt, minimum_score, 1,
+					     &info, dirs_removed);
 	free(mx);
 	trace2_region_leave("diff", "inexact renames", options->repo);
 
  cleanup:
-	/*
-	 * Now that renames have been computed, compute dir_rename_count */
-	if (dirs_removed && dir_rename_count)
-		compute_dir_rename_counts(&info, dirs_removed, dir_rename_count);
-
 	/* At this point, we have found some renames and copies and they
 	 * are recorded in rename_dst.  The original list is still in *q.
 	 */
@@ -1103,6 +1150,7 @@ void diffcore_rename_extended(struct diff_options *options,
 		if (rename_dst[i].filespec_to_free)
 			free_filespec(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);
-- 
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