Signed-off-by: Jonathan Tan <jonathanta...@google.com>
---
 submodule.c | 76 +++++++++++++++++++++++++++++++++++++------------------------
 submodule.h |  3 +++
 2 files changed, 49 insertions(+), 30 deletions(-)

diff --git a/submodule.c b/submodule.c
index bb531e0e5..ce511180e 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1977,16 +1977,24 @@ void absorb_git_dir_into_superproject(const char 
*prefix,
        }
 }
 
-const char *get_superproject_working_tree(void)
+/*
+ * Get the full filename of the gitlink entry corresponding to the
+ * superproject having this repo as a submodule.
+ *
+ * full_name will point to an internal buffer upon success.
+ *
+ * Return 0 if successful, 1 if not (for example, if the parent
+ * directory is not a repo or an unrelated one).
+ */
+int get_superproject_entry(const char **full_name)
 {
+       static struct strbuf sb = STRBUF_INIT;
+
        struct child_process cp = CHILD_PROCESS_INIT;
-       struct strbuf sb = STRBUF_INIT;
        const char *one_up = real_path_if_valid("../");
        const char *cwd = xgetcwd();
-       const char *ret = NULL;
        const char *subpath;
        int code;
-       ssize_t len;
 
        if (!is_inside_work_tree())
                /*
@@ -1994,11 +2002,15 @@ const char *get_superproject_working_tree(void)
                 * We might have a superproject, but it is harder
                 * to determine.
                 */
-               return NULL;
+               return 1;
 
        if (!one_up)
-               return NULL;
+               return 1;
 
+       /*
+        * No need to reset sb, since relative_path() will do it if
+        * necessary.
+        */
        subpath = relative_path(cwd, one_up, &sb);
 
        prepare_submodule_repo_env(&cp.env_array);
@@ -2017,45 +2029,49 @@ const char *get_superproject_working_tree(void)
        if (start_command(&cp))
                die(_("could not start ls-files in .."));
 
-       len = strbuf_read(&sb, cp.out, PATH_MAX);
+       strbuf_read(&sb, cp.out, PATH_MAX);
        close(cp.out);
 
-       if (starts_with(sb.buf, "160000")) {
-               int super_sub_len;
-               int cwd_len = strlen(cwd);
-               char *super_sub, *super_wt;
+       code = finish_command(&cp);
 
+       if (starts_with(sb.buf, "160000")) {
                /*
                 * There is a superproject having this repo as a submodule.
                 * The format is <mode> SP <hash> SP <stage> TAB <full name> \0,
                 * We're only interested in the name after the tab.
                 */
-               super_sub = strchr(sb.buf, '\t') + 1;
-               super_sub_len = sb.buf + sb.len - super_sub - 1;
-
-               if (super_sub_len > cwd_len ||
-                   strcmp(&cwd[cwd_len - super_sub_len], super_sub))
-                       die (_("BUG: returned path string doesn't match cwd?"));
-
-               super_wt = xstrdup(cwd);
-               super_wt[cwd_len - super_sub_len] = '\0';
-
-               ret = real_path(super_wt);
-               free(super_wt);
+               char *tab = strchr(sb.buf, '\t');
+               if (!tab)
+                       die("BUG: ls-files returned line with no tab");
+               *full_name = tab + 1;
+               return 0;
        }
-       strbuf_release(&sb);
-
-       code = finish_command(&cp);
 
        if (code == 128)
                /* '../' is not a git repository */
-               return NULL;
-       if (code == 0 && len == 0)
+               return 1;
+       if (code == 0)
                /* There is an unrelated git repository at '../' */
+               return 1;
+       die(_("ls-tree returned unexpected return code %d"), code);
+}
+
+const char *get_superproject_working_tree(void)
+{
+       const char *full_name;
+       char *super_wt;
+       size_t len;
+       const char *ret;
+
+       if (get_superproject_entry(&full_name))
                return NULL;
-       if (code)
-               die(_("ls-tree returned unexpected return code %d"), code);
 
+       super_wt = xstrdup(xgetcwd());
+       if (!strip_suffix(super_wt, full_name, &len))
+               die("BUG: returned path string doesn't match cwd?");
+       super_wt[len] = '\0';
+       ret = real_path(super_wt);
+       free(super_wt);
        return ret;
 }
 
diff --git a/submodule.h b/submodule.h
index f0da0277a..29ab302cc 100644
--- a/submodule.h
+++ b/submodule.h
@@ -134,6 +134,9 @@ extern void absorb_git_dir_into_superproject(const char 
*prefix,
  * 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.
+ *
+ * The return value, if not NULL, points to the same shared buffer as the one
+ * returned by real_path().
  */
 extern const char *get_superproject_working_tree(void);
 
-- 
2.15.0.531.g2ccb3012c9-goog

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