+/*
+ * read 'path_to_ref' into 'ref'. Also if is_detached is not NULL,
+ * set is_detached to 1 (0) if the ref is detatched (is not detached).
+ *
+ * $GIT_COMMON_DIR/$symref (e.g. HEAD) is practically outside $GIT_DIR so
+ * for linked worktrees, `resolve_ref_unsafe()` won't work (it uses
+ * git_path). Parse the ref ourselves.
+ *
+ * return -1 if the ref is not a proper ref, 0 otherwise (success)
+ */
+static int parse_ref(char *path_to_ref, struct strbuf *ref, int *is_detached)
+{
+ if (is_detached)
+ *is_detached = 0;
+ if (!strbuf_readlink(ref, path_to_ref, 0)) {
+ /* HEAD is symbolic link */
+ if (!starts_with(ref->buf, "refs/") ||
+ check_refname_format(ref->buf, 0))
+ return -1;
+ } else if (strbuf_read_file(ref, path_to_ref, 0) >= 0) {
+ /* textual symref or detached */
+ if (!starts_with(ref->buf, "ref:")) {
+ if (is_detached)
+ *is_detached = 1;
+ } else {
+ strbuf_remove(ref, 0, strlen("ref:"));
+ strbuf_trim(ref);
+ if (check_refname_format(ref->buf, 0))
+ return -1;
+ }
+ } else
+ return -1;
+ return 0;
+}
+
+static char *find_main_symref(const char *symref, const char *branch)
+{
+ struct strbuf sb = STRBUF_INIT;
+ struct strbuf path = STRBUF_INIT;
+ struct strbuf gitdir = STRBUF_INIT;
+ char *existing = NULL;
+
+ strbuf_addf(&path, "%s/%s", get_git_common_dir(), symref);
+ if (parse_ref(path.buf, &sb, NULL) < 0)
+ goto done;
+ if (strcmp(sb.buf, branch))
+ goto done;
+ strbuf_addstr(&gitdir, get_git_common_dir());
+ strbuf_strip_suffix(&gitdir, ".git");
+ existing = strbuf_detach(&gitdir, NULL);
+done:
+ strbuf_release(&path);
+ strbuf_release(&sb);
+ strbuf_release(&gitdir);
+
+ return existing;
+}
+