diffcore-rename: favour identical basenames

When there are several candidates for a rename source, and one of them
has an identical basename to the rename target, take that one.

Noticed by Govind Salinas, posted by Shawn O. Pearce, partial patch
by Linus Torvalds.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diffcore-rename.c

@@ -119,6 +119,21 @@ static int is_exact_match(struct diff_filespec *src,
 	return 0;
 }
 
+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 */
@@ -186,8 +201,11 @@ static int estimate_similarity(struct diff_filespec *src,
 	 */
 	if (!dst->size)
 		score = 0; /* should not happen */
-	else
+	else {
 		score = (int)(src_copied * MAX_SCORE / max_size);
+		if (basename_same(src, dst))
+			score++;
+	}
 	return score;
 }
 
@@ -295,9 +313,22 @@ void diffcore_rename(struct diff_options *options)
 			if (rename_dst[i].pair)
 				continue; /* dealt with an earlier round */
 			for (j = 0; j < rename_src_nr; j++) {
+				int k;
 				struct diff_filespec *one = rename_src[j].one;
 				if (!is_exact_match(one, two, contents_too))
 					continue;
+
+				/* see if there is a basename match, too */
+				for (k = j; k < rename_src_nr; k++) {
+					one = rename_src[k].one;
+					if (basename_same(one, two) &&
+						is_exact_match(one, two,
+							contents_too)) {
+						j = k;
+						break;
+					}
+				}
+
 				record_rename_pair(i, j, (int)MAX_SCORE);
 				rename_count++;
 				break; /* we are done with this entry */

t/t4001-diff-rename.sh

@@ -64,4 +64,17 @@ test_expect_success \
     'validate the output.' \
     'compare_diff_patch current expected'
 
+test_expect_success 'favour same basenames over different ones' '
+	cp path1 another-path &&
+	git add another-path &&
+	git commit -m 1 &&
+	git rm path1 &&
+	mkdir subdir &&
+	git mv another-path subdir/path1 &&
+	git runstatus | grep "renamed: .*path1 -> subdir/path1"'
+
+test_expect_success  'favour same basenames even with minor differences' '
+	git show HEAD:path1 | sed "s/15/16/" > subdir/path1 &&
+	git runstatus | grep "renamed: .*path1 -> subdir/path1"'
+
 test_done