Guess the default branch based on current namespace

resolve_ref_unsafe() can't be told to be namespace aware,
so we need to prepend the namespace beforehand.

Additionally, we need to add the RESOLVE_REF_NO_RECURSE flag,
since otherwise if the commit that is pointed to exists in the root namespace,
it will opt to return that rather than the value in the namespace,
presumably preferring shorter ref names to longer ones.

Signed-off-by: Richard Maw <richard.maw@gmail.com>

cgit.c

@@ -474,11 +474,17 @@ static char *guess_defbranch(void)
 {
 	const char *ref;
 	unsigned char sha1[20];
-
-	ref = resolve_ref_unsafe("HEAD", 0, sha1, NULL);
-	if (!ref || !starts_with(ref, "refs/heads/"))
+	char *namespaced_head = NULL;
+
+	if (get_git_namespace())
+		namespaced_head = mkpathdup("%sHEAD", get_git_namespace());
+	/* NOTE: RESOLVE_REF_NO_RECURSE is required to prevent it resolving HEAD
+	   into a ref outside of the namespace. */
+	ref = resolve_ref_unsafe(namespaced_head ?: "HEAD", RESOLVE_REF_NO_RECURSE, sha1, NULL);
+	free(namespaced_head);
+	if (!ref || !starts_with(strip_namespace(ref), "refs/heads/"))
 		return "master";
-	return xstrdup(ref + 11);
+	return xstrdup(strip_namespace(ref) + 11);
 }
 /* The caller must free filename and ref after calling this. */
 static inline void parse_readme(const char *readme, char **filename, char **ref, struct cgit_repo *repo)