get_superproject_working_tree(): return strbuf

Together with the previous commits, this commit fully fixes the problem
of using shared buffer for `real_path()` in `get_superproject_working_tree()`.

Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rev-parse.c

diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 06ca717..0605643 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -808,9 +808,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				continue;
 			}
 			if (!strcmp(arg, "--show-superproject-working-tree")) {
-				const char *superproject = get_superproject_working_tree();
-				if (superproject)
-					puts(superproject);
+				struct strbuf superproject = STRBUF_INIT;
+				if (get_superproject_working_tree(&superproject))
+					puts(superproject.buf);
+				strbuf_release(&superproject);
 				continue;
 			}
 			if (!strcmp(arg, "--show-prefix")) {

submodule.c

diff --git a/submodule.c b/submodule.c
index 215c625..c3aadf3 100644
--- a/submodule.c
+++ b/submodule.c
@@ -2168,14 +2168,13 @@ void absorb_git_dir_into_superproject(const char *path,
 	}
 }
 
-const char *get_superproject_working_tree(void)
+int get_superproject_working_tree(struct strbuf *buf)
 {
-	static struct strbuf realpath = STRBUF_INIT;
 	struct child_process cp = CHILD_PROCESS_INIT;
 	struct strbuf sb = STRBUF_INIT;
 	struct strbuf one_up = STRBUF_INIT;
 	const char *cwd = xgetcwd();
-	const char *ret = NULL;
+	int ret = 0;
 	const char *subpath;
 	int code;
 	ssize_t len;
@@ -2186,10 +2185,10 @@ const char *get_superproject_working_tree(void)
 		 * We might have a superproject, but it is harder
 		 * to determine.
 		 */
-		return NULL;
+		return 0;
 
 	if (!strbuf_realpath(&one_up, "../", 0))
-		return NULL;
+		return 0;
 
 	subpath = relative_path(cwd, one_up.buf, &sb);
 	strbuf_release(&one_up);
@@ -2233,8 +2232,8 @@ const char *get_superproject_working_tree(void)
 		super_wt = xstrdup(cwd);
 		super_wt[cwd_len - super_sub_len] = '\0';
 
-		strbuf_realpath(&realpath, super_wt, 1);
-		ret = realpath.buf;
+		strbuf_realpath(buf, super_wt, 1);
+		ret = 1;
 		free(super_wt);
 	}
 	strbuf_release(&sb);
@@ -2243,10 +2242,10 @@ const char *get_superproject_working_tree(void)
 
 	if (code == 128)
 		/* '../' is not a git repository */
-		return NULL;
+		return 0;
 	if (code == 0 && len == 0)
 		/* There is an unrelated git repository at '../' */
-		return NULL;
+		return 0;
 	if (code)
 		die(_("ls-tree returned unexpected return code %d"), code);
 

submodule.h

diff --git a/submodule.h b/submodule.h
index c81ec1a..4dad649 100644
--- a/submodule.h
+++ b/submodule.h
@@ -152,8 +152,8 @@ void absorb_git_dir_into_superproject(const char *path,
 /*
  * Return the absolute path of the working tree of the superproject, which this
  * project is a submodule of. If this repository is not a submodule of
- * another repository, return NULL.
+ * another repository, return 0.
  */
-const char *get_superproject_working_tree(void);
+int get_superproject_working_tree(struct strbuf *buf);
 
 #endif