submodule helper list: respect correct path prefix

This is a regression introduced by 74703a1e4d (submodule: rewrite
`module_list` shell function in C, 2015-09-02).

Add a test to ensure we list the right submodule when giving a
specific pathspec.

Reported-By: Caleb Jorden <cjorden@gmail.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/submodule--helper.c

@@ -22,17 +22,12 @@ static int module_list_compute(int argc, const char **argv,
 			       struct module_list *list)
 {
 	int i, result = 0;
-	char *max_prefix, *ps_matched = NULL;
-	int max_prefix_len;
+	char *ps_matched = NULL;
 	parse_pathspec(pathspec, 0,
 		       PATHSPEC_PREFER_FULL |
 		       PATHSPEC_STRIP_SUBMODULE_SLASH_CHEAP,
 		       prefix, argv);
 
-	/* Find common prefix for all pathspec's */
-	max_prefix = common_prefix(pathspec);
-	max_prefix_len = max_prefix ? strlen(max_prefix) : 0;
-
 	if (pathspec->nr)
 		ps_matched = xcalloc(pathspec->nr, 1);
 
@@ -44,7 +39,7 @@ static int module_list_compute(int argc, const char **argv,
 
 		if (!S_ISGITLINK(ce->ce_mode) ||
 		    !match_pathspec(pathspec, ce->name, ce_namelen(ce),
-				    max_prefix_len, ps_matched, 1))
+				    0, ps_matched, 1))
 			continue;
 
 		ALLOC_GROW(list->entries, list->nr + 1, list->alloc);
@@ -57,7 +52,6 @@ static int module_list_compute(int argc, const char **argv,
 			 */
 			i++;
 	}
-	free(max_prefix);
 
 	if (ps_matched && report_path_error(ps_matched, pathspec, prefix))
 		result = -1;

t/t7400-submodule-basic.sh

@@ -999,5 +999,30 @@ test_expect_success 'submodule add clone shallow submodule' '
 	)
 '
 
+test_expect_success 'submodule helper list is not confused by common prefixes' '
+	mkdir -p dir1/b &&
+	(
+		cd dir1/b &&
+		git init &&
+		echo hi >testfile2 &&
+		git add . &&
+		git commit -m "test1"
+	) &&
+	mkdir -p dir2/b &&
+	(
+		cd dir2/b &&
+		git init &&
+		echo hello >testfile1 &&
+		git add .  &&
+		git commit -m "test2"
+	) &&
+	git submodule add /dir1/b dir1/b &&
+	git submodule add /dir2/b dir2/b &&
+	git commit -m "first submodule commit" &&
+	git submodule--helper list dir1/b |cut -c51- >actual &&
+	echo "dir1/b" >expect &&
+	test_cmp expect actual
+'
+
 
 test_done