merge-file: fix memory leaks on error path

Fix a memory leak in "merge-file", we need to loop over the "mmfs"
array and free() what we've got so far when we error out. As a result
we can mark a test as passing with SANITIZE=leak using
"TEST_PASSES_SANITIZE_LEAK=true".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge-file.c

@@ -87,7 +87,8 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 
 		free(fname);
 		if (ret)
-			return ret;
+			goto cleanup;
+
 	}
 
 	xmp.ancestor = names[1];
@@ -95,9 +96,6 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 	xmp.file2 = names[2];
 	ret = xdl_merge(mmfs + 1, mmfs + 0, mmfs + 2, &xmp, &result);
 
-	for (i = 0; i < 3; i++)
-		free(mmfs[i].ptr);
-
 	if (ret >= 0) {
 		const char *filename = argv[0];
 		char *fpath = prefix_filename(prefix, argv[0]);
@@ -118,5 +116,9 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 	if (ret > 127)
 		ret = 127;
 
+cleanup:
+	for (i = 0; i < 3; i++)
+		free(mmfs[i].ptr);
+
 	return ret;
 }

t/t6403-merge-file.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
 test_description='RCS merge replacement: merge-file'
+
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'setup' '