Merge branch 'en/merge-dual-dir-renames-fix' into maint

Fixes a long-standing corner case bug around directory renames in
the merge-ort strategy.
source: <pull.1268.v4.git.1656984823.gitgitgadget@gmail.com>

* en/merge-dual-dir-renames-fix:
  merge-ort: fix issue with dual rename and add/add conflict
  merge-ort: shuffle the computation and cleanup of potential collisions
  merge-ort: make a separate function for freeing struct collisions
  merge-ort: small cleanups of check_for_directory_rename
  t6423: add tests of dual directory rename plus add/add conflict

merge-ort.c

@@ -2260,6 +2260,27 @@ static void compute_collisions(struct strmap *collisions,
 	}
 }
 
+static void free_collisions(struct strmap *collisions)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+
+	/* Free each value in the collisions map */
+	strmap_for_each_entry(collisions, &iter, entry) {
+		struct collision_info *info = entry->value;
+		string_list_clear(&info->source_files, 0);
+	}
+	/*
+	 * In compute_collisions(), we set collisions.strdup_strings to 0
+	 * so that we wouldn't have to make another copy of the new_path
+	 * allocated by apply_dir_rename().  But now that we've used them
+	 * and have no other references to these strings, it is time to
+	 * deallocate them.
+	 */
+	free_strmap_strings(collisions);
+	strmap_clear(collisions, 1);
+}
+
 static char *check_for_directory_rename(struct merge_options *opt,
 					const char *path,
 					unsigned side_index,
@@ -2268,18 +2289,23 @@ static char *check_for_directory_rename(struct merge_options *opt,
 					struct strmap *collisions,
 					int *clean_merge)
 {
-	char *new_path = NULL;
+	char *new_path;
 	struct strmap_entry *rename_info;
-	struct strmap_entry *otherinfo = NULL;
+	struct strmap_entry *otherinfo;
 	const char *new_dir;
+	int other_side = 3 - side_index;
 
+	/*
+	 * Cases where we don't have or don't want a directory rename for
+	 * this path.
+	 */
 	if (strmap_empty(dir_renames))
-		return new_path;
+		return NULL;
+	if (strmap_get(&collisions[other_side], path))
+		return NULL;
 	rename_info = check_dir_renamed(path, dir_renames);
 	if (!rename_info)
-		return new_path;
-	/* old_dir = rename_info->key; */
-	new_dir = rename_info->value;
+		return NULL;
 
 	/*
 	 * This next part is a little weird.  We do not want to do an
@@ -2305,6 +2331,7 @@ static char *check_for_directory_rename(struct merge_options *opt,
 	 * As it turns out, this also prevents N-way transient rename
 	 * confusion; See testcases 9c and 9d of t6043.
 	 */
+	new_dir = rename_info->value; /* old_dir = rename_info->key; */
 	otherinfo = strmap_get_entry(dir_rename_exclusions, new_dir);
 	if (otherinfo) {
 		path_msg(opt, rename_info->key, 1,
@@ -2315,7 +2342,8 @@ static char *check_for_directory_rename(struct merge_options *opt,
 	}
 
 	new_path = handle_path_level_conflicts(opt, path, side_index,
-					       rename_info, collisions);
+					       rename_info,
+					       &collisions[side_index]);
 	*clean_merge &= (new_path != NULL);
 
 	return new_path;
@@ -3024,18 +3052,15 @@ static int detect_regular_renames(struct merge_options *opt,
 static int collect_renames(struct merge_options *opt,
 			   struct diff_queue_struct *result,
 			   unsigned side_index,
+			   struct strmap *collisions,
 			   struct strmap *dir_renames_for_side,
 			   struct strmap *rename_exclusions)
 {
 	int i, clean = 1;
-	struct strmap collisions;
 	struct diff_queue_struct *side_pairs;
-	struct hashmap_iter iter;
-	struct strmap_entry *entry;
 	struct rename_info *renames = &opt->priv->renames;
 
 	side_pairs = &renames->pairs[side_index];
-	compute_collisions(&collisions, dir_renames_for_side, side_pairs);
 
 	for (i = 0; i < side_pairs->nr; ++i) {
 		struct diff_filepair *p = side_pairs->queue[i];
@@ -3051,7 +3076,7 @@ static int collect_renames(struct merge_options *opt,
 						      side_index,
 						      dir_renames_for_side,
 						      rename_exclusions,
-						      &collisions,
+						      collisions,
 						      &clean);
 
 		possibly_cache_new_pair(renames, p, side_index, new_path);
@@ -3077,20 +3102,6 @@ static int collect_renames(struct merge_options *opt,
 		result->queue[result->nr++] = p;
 	}
 
-	/* Free each value in the collisions map */
-	strmap_for_each_entry(&collisions, &iter, entry) {
-		struct collision_info *info = entry->value;
-		string_list_clear(&info->source_files, 0);
-	}
-	/*
-	 * In compute_collisions(), we set collisions.strdup_strings to 0
-	 * so that we wouldn't have to make another copy of the new_path
-	 * allocated by apply_dir_rename().  But now that we've used them
-	 * and have no other references to these strings, it is time to
-	 * deallocate them.
-	 */
-	free_strmap_strings(&collisions);
-	strmap_clear(&collisions, 1);
 	return clean;
 }
 
@@ -3101,6 +3112,7 @@ static int detect_and_process_renames(struct merge_options *opt,
 {
 	struct diff_queue_struct combined = { 0 };
 	struct rename_info *renames = &opt->priv->renames;
+	struct strmap collisions[3];
 	int need_dir_renames, s, i, clean = 1;
 	unsigned detection_run = 0;
 
@@ -3150,12 +3162,22 @@ static int detect_and_process_renames(struct merge_options *opt,
 	ALLOC_GROW(combined.queue,
 		   renames->pairs[1].nr + renames->pairs[2].nr,
 		   combined.alloc);
+	for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++) {
+		int other_side = 3 - i;
+		compute_collisions(&collisions[i],
+				   &renames->dir_renames[other_side],
+				   &renames->pairs[i]);
+	}
 	clean &= collect_renames(opt, &combined, MERGE_SIDE1,
+				 collisions,
 				 &renames->dir_renames[2],
 				 &renames->dir_renames[1]);
 	clean &= collect_renames(opt, &combined, MERGE_SIDE2,
+				 collisions,
 				 &renames->dir_renames[1],
 				 &renames->dir_renames[2]);
+	for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++)
+		free_collisions(&collisions[i]);
 	STABLE_QSORT(combined.queue, combined.nr, compare_pairs);
 	trace2_region_leave("merge", "directory renames", opt->repo);
 

t/t6423-merge-rename-directories.sh

@@ -5199,6 +5199,111 @@ test_expect_success '12k: Directory rename with sibling causes rename-to-self' '
 	)
 '
 
+# Testcase 12l, Both sides rename a directory into the other side, both add
+#   a file which after directory renames are the same filename
+#   Commit O: sub1/file,                 sub2/other
+#   Commit A: sub3/file,                 sub2/{other, new_add_add_file_1}
+#   Commit B: sub1/{file, newfile}, sub1/sub2/{other, new_add_add_file_2}
+#
+#   In words:
+#     A: sub1/ -> sub3/, add sub2/new_add_add_file_1
+#     B: sub2/ -> sub1/sub2, add sub1/newfile, add sub1/sub2/new_add_add_file_2
+#
+#   Expected: sub3/{file, newfile, sub2/other}
+#             CONFLICT (add/add): sub1/sub2/new_add_add_file
+#
+#   Note that sub1/newfile is not extraneous.  Directory renames are only
+#   detected if they are needed, and they are only needed if the old directory
+#   had a new file added on the opposite side of history.  So sub1/newfile
+#   is needed for there to be a sub1/ -> sub3/ rename.
+
+test_setup_12l () {
+	test_create_repo 12l_$1 &&
+	(
+		cd 12l_$1 &&
+
+		mkdir sub1 sub2
+		echo file >sub1/file &&
+		echo other >sub2/other &&
+		git add sub1 sub2 &&
+		git commit -m "O" &&
+
+		git branch O &&
+		git branch A &&
+		git branch B &&
+
+		git checkout A &&
+		git mv sub1 sub3 &&
+		echo conflicting >sub2/new_add_add_file &&
+		git add sub2 &&
+		test_tick &&
+		git add -u &&
+		git commit -m "A" &&
+
+		git checkout B &&
+		echo dissimilar >sub2/new_add_add_file &&
+		echo brand >sub1/newfile &&
+		git add sub1 sub2 &&
+		git mv sub2 sub1 &&
+		test_tick &&
+		git commit -m "B"
+	)
+}
+
+test_expect_merge_algorithm failure success '12l (B into A): Rename into each other + add/add conflict' '
+	test_setup_12l BintoA &&
+	(
+		cd 12l_BintoA &&
+
+		git checkout -q A^0 &&
+
+		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 &&
+
+		test_stdout_line_count = 5 git ls-files -s &&
+
+		git rev-parse >actual \
+			:0:sub3/file :0:sub3/newfile :0:sub3/sub2/other \
+			:2:sub1/sub2/new_add_add_file \
+			:3:sub1/sub2/new_add_add_file &&
+		git rev-parse >expect \
+			O:sub1/file  B:sub1/newfile O:sub2/other \
+			A:sub2/new_add_add_file \
+			B:sub1/sub2/new_add_add_file &&
+		test_cmp expect actual &&
+
+		git ls-files -o >actual &&
+		test_write_lines actual expect >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_merge_algorithm failure success '12l (A into B): Rename into each other + add/add conflict' '
+	test_setup_12l AintoB &&
+	(
+		cd 12l_AintoB &&
+
+		git checkout -q B^0 &&
+
+		test_must_fail git -c merge.directoryRenames=true merge -s recursive A^0 &&
+
+		test_stdout_line_count = 5 git ls-files -s &&
+
+		git rev-parse >actual \
+			:0:sub3/file :0:sub3/newfile :0:sub3/sub2/other \
+			:2:sub1/sub2/new_add_add_file \
+			:3:sub1/sub2/new_add_add_file &&
+		git rev-parse >expect \
+			O:sub1/file  B:sub1/newfile O:sub2/other \
+			B:sub1/sub2/new_add_add_file \
+			A:sub2/new_add_add_file &&
+		test_cmp expect actual &&
+
+		git ls-files -o >actual &&
+		test_write_lines actual expect >expect &&
+		test_cmp expect actual
+	)
+'
+
 ###########################################################################
 # SECTION 13: Checking informational and conflict messages
 #