submodule: look up remotes by URL first

The get_default_remote_submodule() function performs a lookup to find
the appropriate remote to use within a submodule. The function first
checks to see if it can find the remote for the current branch. If this
fails, it then checks to see if there is exactly one remote. It will use
this, before finally falling back to "origin" as the default.

If a user happens to rename their default remote from origin, either
manually or by setting something like clone.defaultRemoteName, this
fallback will not work.

In such cases, the submodule logic will try to use a non-existent
remote. This usually manifests as a failure to trigger the submodule
update.

The parent project already knows and stores the submodule URL in either
.gitmodules or its .git/config.

Add a new repo_remote_from_url() helper which will iterate over all the
remotes in a repository and return the first remote which has a matching
URL.

Refactor get_default_remote_submodule to find the submodule and get its
URL. If a valid URL exists, first try to obtain a remote using the new
repo_remote_from_url(). Fall back to the repo_default_remote()
otherwise.

The fallback logic is kept in case for some reason the user has manually
changed the URL within the submodule. Additionally, we still try to use
a remote rather than directly passing the URL in the
fetch_in_submodule() logic. This ensures that an update will properly
update the remote refs within the submodule as expected, rather than
just fetching into FETCH_HEAD.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/submodule--helper.c

@@ -72,16 +72,40 @@ static char *resolve_relative_url(const char *rel_url, const char *up_path, int
 
 static int get_default_remote_submodule(const char *module_path, char **default_remote)
 {
+	const struct submodule *sub;
 	struct repository subrepo;
+	const char *remote_name = NULL;
+	char *url = NULL;
+
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), module_path);
+	if (sub && sub->url) {
+		url = xstrdup(sub->url);
+
+		/* Possibly a url relative to parent */
+		if (starts_with_dot_dot_slash(url) ||
+		    starts_with_dot_slash(url)) {
+			char *oldurl = url;
+
+			url = resolve_relative_url(oldurl, NULL, 1);
+			free(oldurl);
+		}
+	}
 
 	if (repo_submodule_init(&subrepo, the_repository, module_path,
 				null_oid(the_hash_algo)) < 0)
 		return die_message(_("could not get a repository handle for submodule '%s'"),
 				   module_path);
 
-	*default_remote = xstrdup(repo_default_remote(&subrepo));
+	/* Look up by URL first */
+	if (url)
+		remote_name = repo_remote_from_url(&subrepo, url);
+	if (!remote_name)
+		remote_name = repo_default_remote(&subrepo);
+
+	*default_remote = xstrdup(remote_name);
 
 	repo_clear(&subrepo);
+	free(url);
 
 	return 0;
 }

remote.c

@@ -1801,6 +1801,21 @@ const char *repo_default_remote(struct repository *repo)
 	return remotes_remote_for_branch(repo->remote_state, branch, NULL);
 }
 
+const char *repo_remote_from_url(struct repository *repo, const char *url)
+{
+	read_config(repo, 0);
+
+	for (int i = 0; i < repo->remote_state->remotes_nr; i++) {
+		struct remote *remote = repo->remote_state->remotes[i];
+		if (!remote)
+			continue;
+
+		if (remote_has_url(remote, url))
+			return remote->name;
+	}
+	return NULL;
+}
+
 int branch_has_merge_config(struct branch *branch)
 {
 	return branch && branch->set_merge;

remote.h

@@ -340,6 +340,7 @@ const char *pushremote_for_branch(struct branch *branch, int *explicit);
 char *remote_ref_for_branch(struct branch *branch, int for_push);
 
 const char *repo_default_remote(struct repository *repo);
+const char *repo_remote_from_url(struct repository *repo, const char *url);
 
 /* returns true if the given branch has merge configuration given. */
 int branch_has_merge_config(struct branch *branch);

t/t7406-submodule-update.sh

@@ -1134,6 +1134,38 @@ test_expect_success 'setup clean recursive superproject' '
 	git clone --recurse-submodules top top-clean
 '
 
+test_expect_success 'submodule update with multiple remotes' '
+	test_when_finished "rm -fr top-cloned" &&
+	cp -r top-clean top-cloned &&
+
+	# Create a commit in each repo, starting with bottom
+	test_commit -C bottom multiple_remote_commit &&
+	# Create middle commit
+	git -C middle/bottom fetch &&
+	git -C middle/bottom checkout -f FETCH_HEAD &&
+	git -C middle add bottom &&
+	git -C middle commit -m "multiple_remote_commit" &&
+	# Create top commit
+	git -C top/middle fetch &&
+	git -C top/middle checkout -f FETCH_HEAD &&
+	git -C top add middle &&
+	git -C top commit -m "multiple_remote_commit" &&
+
+	# rename the submodule remote
+	git -C top-cloned/middle remote rename origin upstream &&
+
+	# Add another remote
+	git -C top-cloned/middle remote add other bogus &&
+
+	# Make the update of "middle" a no-op, otherwise we error out
+	# because of its unmerged state
+	test_config -C top-cloned submodule.middle.update !true &&
+	git -C top-cloned submodule update --recursive 2>actual.err &&
+	cat >expect.err <<-\EOF &&
+	EOF
+	test_cmp expect.err actual.err
+'
+
 test_expect_success 'submodule update with renamed remote' '
 	test_when_finished "rm -fr top-cloned" &&
 	cp -r top-clean top-cloned &&