diffcore-rename: check if we have enough renames for directories early on

As noted in the past two commits, we only need to track dir_rename_count
for directories that we directly need directory renames for.  Further,
now that we are tracking the number of unmatched pairs for each
directory left to count, we can determine if a directory already has
enough renames to determine how directory rename detection will go for
that directory.  For such directories, demote them from
RELEVANT_FOR_SELF to RELEVANT_FOR_ANCESTOR, as there still may be an
ancestor of that directory that we need renames for.

The next commit will use this information to update individual paths in
relevant_sources.

Signed-off-by: Elijah Newren <[email protected]>

Author: newren

diffcore-rename.c

@@ -409,6 +409,26 @@ static const char *get_highest_rename_path(struct strintmap *counts)
 
 static 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,
 			    char *old_dir,
 			    char *new_dir)
@@ -1103,6 +1123,8 @@ static void handle_early_known_dir_renames(struct dir_rename_info *info,
 					   struct strintmap *dirs_removed)
 {
 	int i;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
 
 	if (!dirs_removed || !relevant_sources)
 		return; /* nothing to cull */
@@ -1138,6 +1160,18 @@ static void handle_early_known_dir_renames(struct dir_rename_info *info,
 		 */
 		free(old_dir);
 	}
+
+	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);
+		}
+	}
 }
 
 void diffcore_rename_extended(struct diff_options *options,