submodule: migrate get_next_submodule to use repository structs

We used to recurse into submodules, even if they were broken having
only an objects directory. The child process executed in the submodule
would fail though if the submodule was broken. This is tested via
"fetching submodule into a broken repository" in t5526.

This patch tightens the check upfront, such that we do not need
to spawn a child process to find out if the submodule is broken.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule.c

@@ -1253,6 +1253,30 @@ static int get_fetch_recurse_config(const struct submodule *submodule,
 	return spf->default_option;
 }
 
+static struct repository *get_submodule_repo_for(struct repository *r,
+						 const struct submodule *sub)
+{
+	struct repository *ret = xmalloc(sizeof(*ret));
+
+	if (repo_submodule_init(ret, r, sub)) {
+		/*
+		 * No entry in .gitmodules? Technically not a submodule,
+		 * but historically we supported repositories that happen to be
+		 * in-place where a gitlink is. Keep supporting them.
+		 */
+		struct strbuf gitdir = STRBUF_INIT;
+		strbuf_repo_worktree_path(&gitdir, r, "%s/.git", sub->path);
+		if (repo_init(ret, gitdir.buf, NULL)) {
+			strbuf_release(&gitdir);
+			free(ret);
+			return NULL;
+		}
+		strbuf_release(&gitdir);
+	}
+
+	return ret;
+}
+
 static int get_next_submodule(struct child_process *cp,
 			      struct strbuf *err, void *data, void **task_cb)
 {
@@ -1260,12 +1284,11 @@ static int get_next_submodule(struct child_process *cp,
 	struct submodule_parallel_fetch *spf = data;
 
 	for (; spf->count < spf->r->index->cache_nr; spf->count++) {
-		struct strbuf submodule_path = STRBUF_INIT;
-		struct strbuf submodule_git_dir = STRBUF_INIT;
 		struct strbuf submodule_prefix = STRBUF_INIT;
 		const struct cache_entry *ce = spf->r->index->cache[spf->count];
-		const char *git_dir, *default_argv;
+		const char *default_argv;
 		const struct submodule *submodule;
+		struct repository *repo;
 		struct submodule default_submodule = SUBMODULE_INIT;
 
 		if (!S_ISGITLINK(ce->ce_mode))
@@ -1300,15 +1323,11 @@ static int get_next_submodule(struct child_process *cp,
 			continue;
 		}
 
-		strbuf_repo_worktree_path(&submodule_path, spf->r, "%s", ce->name);
-		strbuf_addf(&submodule_git_dir, "%s/.git", submodule_path.buf);
 		strbuf_addf(&submodule_prefix, "%s%s/", spf->prefix, ce->name);
-		git_dir = read_gitfile(submodule_git_dir.buf);
-		if (!git_dir)
-			git_dir = submodule_git_dir.buf;
-		if (is_directory(git_dir)) {
+		repo = get_submodule_repo_for(spf->r, submodule);
+		if (repo) {
 			child_process_init(cp);
-			cp->dir = strbuf_detach(&submodule_path, NULL);
+			cp->dir = xstrdup(repo->worktree);
 			prepare_submodule_repo_env(&cp->env_array);
 			cp->git_cmd = 1;
 			if (!spf->quiet)
@@ -1319,10 +1338,23 @@ static int get_next_submodule(struct child_process *cp,
 			argv_array_push(&cp->args, default_argv);
 			argv_array_push(&cp->args, "--submodule-prefix");
 			argv_array_push(&cp->args, submodule_prefix.buf);
+
+			repo_clear(repo);
+			free(repo);
 			ret = 1;
+		} else {
+			/*
+			 * An empty directory is normal,
+			 * the submodule is not initialized
+			 */
+			if (S_ISGITLINK(ce->ce_mode) &&
+			    !is_empty_dir(ce->name)) {
+				spf->result = 1;
+				strbuf_addf(err,
+					    _("Could not access submodule '%s'"),
+					    ce->name);
+			}
 		}
-		strbuf_release(&submodule_path);
-		strbuf_release(&submodule_git_dir);
 		strbuf_release(&submodule_prefix);
 		if (ret) {
 			spf->count++;