[PATCH 2/2] remote: resolve URL-valued push tracking remotes

["Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Harald Nordgren <haraldnordgren@gmail.com>

A branch may name its push destination with a URL instead of a
configured remote. This is useful in fork workflows, where the original
remote is renamed to "upstream", the fork is added as "origin", and an
existing branch.<name>.pushRemote continues to contain the fork URL.

Git can still push through the anonymous remote created for that URL.
However, the anonymous remote has no fetch refspec. Git therefore cannot
resolve @{push} to origin/<branch> or update that remote-tracking branch
after a push. The push can succeed, or report that everything is up to
date, while status continues to compare against a stale tracking ref or
cannot show the push branch at all.

A uniquely matching configured remote already provides the missing
mapping. Use its fetch refspec when resolving the push tracking branch
and when updating tracking refs after a push. This changes neither the
push destination nor configuration. Keep the existing behavior when no
remote matches or multiple remotes share the URL, since either case is
ambiguous.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/revisions.adoc |   3 +
 remote.c                     |  27 ++++++++-
 remote.h                     |   2 +
 t/t5505-remote.sh            | 104 +++++++++++++++++++++++++++++++++++
 transport.c                  |   5 +-
 5 files changed, 139 insertions(+), 2 deletions(-)

diff --git a/Documentation/revisions.adoc b/Documentation/revisions.adoc
index 6ea6c7cead..b691691c8c 100644
--- a/Documentation/revisions.adoc
+++ b/Documentation/revisions.adoc
@@ -127,6 +127,9 @@ some output processing may assume ref names in UTF-8.
   `git push` were run while `branchname` was checked out (or the current
   `HEAD` if no branchname is specified). Like for '@\{upstream\}', we report
   the remote-tracking branch that corresponds to that branch at the remote.
+  If the push remote is specified as a URL, the fetch refspec of a uniquely
+  matching configured remote is used to find and update the remote-tracking
+  branch.
 +
 Here's an example to make it more clear:
 +
diff --git a/remote.c b/remote.c
index 89d0f9e2d8..03908dfe8d 100644
--- a/remote.c
+++ b/remote.c
@@ -1887,13 +1887,38 @@ const char *branch_get_upstream(struct branch *branch, struct strbuf *err)
 	return branch->merge[0]->dst;
 }
 
-static char *tracking_for_push_dest(struct repository *repo UNUSED,
+struct remote *repo_remote_for_push_tracking(struct repository *repo,
+					     struct remote *remote)
+{
+	struct remote *first_match = NULL;
+	struct remote_state *remote_state = repo->remote_state;
+
+	if (remote->origin != REMOTE_UNCONFIGURED || remote->url.nr != 1)
+		return remote;
+
+	for (int i = 0; i < remote_state->remotes_nr; i++) {
+		struct remote *candidate = remote_state->remotes[i];
+
+		if (!candidate || candidate == remote ||
+		    !remote_is_configured(candidate, 0) ||
+		    !remote_has_url(candidate, remote->url.v[0]))
+			continue;
+		if (first_match)
+			return remote;
+		first_match = candidate;
+	}
+
+	return first_match ? first_match : remote;
+}
+
+static char *tracking_for_push_dest(struct repository *repo,
 				    struct remote *remote,
 				    const char *refname,
 				    struct strbuf *err)
 {
 	char *ret;
 
+	remote = repo_remote_for_push_tracking(repo, remote);
 	ret = apply_refspecs(&remote->fetch, refname);
 	if (!ret)
 		return error_buf(err,
diff --git a/remote.h b/remote.h
index 72a54d84ad..cca02033b9 100644
--- a/remote.h
+++ b/remote.h
@@ -345,6 +345,8 @@ 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);
+struct remote *repo_remote_for_push_tracking(struct repository *repo,
+					     struct remote *remote);
 
 /* returns true if the given branch has merge configuration given. */
 int branch_has_merge_config(struct branch *branch);
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index e592c0bcde..e16b3f320a 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -24,6 +24,28 @@ setup_repository () {
 	)
 }
 
+setup_url_pushremote () {
+	rm -rf fork.git client &&
+	git clone --bare one fork.git &&
+	git clone one client &&
+	fork_url="$TRASH_DIRECTORY/fork.git" &&
+	(
+		cd client &&
+		git checkout -b topic --track origin/main &&
+		git commit --allow-empty -m topic-change &&
+		git config push.default current &&
+		git config status.compareBranches "@{upstream} @{push}" &&
+		git config branch.topic.pushRemote "$fork_url" &&
+		git push
+	)
+}
+
+check_status () {
+	git -C client status >actual &&
+	cat >expected &&
+	test_cmp expected actual
+}
+
 tokens_match () {
 	echo "$1" | tr ' ' '\012' | sort | sed -e '/^$/d' >expect &&
 	echo "$2" | tr ' ' '\012' | sort | sed -e '/^$/d' >actual &&
@@ -1018,6 +1040,88 @@ test_expect_success 'rename a remote renames repo remote.pushDefault but keeps g
 	)
 '
 
+test_expect_success 'URL-valued pushRemote without matching remote is not trackable' '
+	setup_url_pushremote &&
+
+	check_status <<-EOF
+	On branch topic
+	Your branch is ahead of ${SQ}origin/main${SQ} by 1 commit.
+	  (use "git push" to publish your local commits)
+
+	nothing to commit, working tree clean
+	EOF
+'
+
+test_expect_success 'adding fork remote makes URL-valued pushRemote trackable' '
+	setup_url_pushremote &&
+
+	(
+		cd client &&
+		git remote rename origin upstream &&
+		git remote add -f origin "$fork_url"
+	) &&
+
+	check_status <<-EOF
+	On branch topic
+	Your branch is ahead of ${SQ}upstream/main${SQ} by 1 commit.
+
+	Your branch is up to date with ${SQ}origin/topic${SQ}.
+
+	nothing to commit, working tree clean
+	EOF
+'
+
+test_expect_success 'up-to-date URL push refreshes stale tracking branch' '
+	setup_url_pushremote &&
+	(
+		cd client &&
+		git remote rename origin upstream &&
+		git remote add -f origin "$fork_url" &&
+		git commit --allow-empty -m another-topic-change &&
+		git -C ../fork.git fetch ../client topic:topic
+	) &&
+
+	check_status <<-EOF &&
+	On branch topic
+	Your branch is ahead of ${SQ}upstream/main${SQ} by 2 commits.
+
+	Your branch is ahead of ${SQ}origin/topic${SQ} by 1 commit.
+	  (use "git push" to publish your local commits)
+
+	nothing to commit, working tree clean
+	EOF
+
+	git -C client push >actual 2>&1 &&
+	test_grep "Everything up-to-date" actual &&
+
+	check_status <<-EOF
+	On branch topic
+	Your branch is ahead of ${SQ}upstream/main${SQ} by 2 commits.
+
+	Your branch is up to date with ${SQ}origin/topic${SQ}.
+
+	nothing to commit, working tree clean
+	EOF
+'
+
+test_expect_success 'duplicate remote URL leaves URL-valued pushRemote ambiguous' '
+	setup_url_pushremote &&
+	(
+		cd client &&
+		git remote rename origin upstream &&
+		git remote add -f origin "$fork_url" &&
+		git remote add duplicate "$fork_url"
+	) &&
+
+	check_status <<-EOF
+	On branch topic
+	Your branch is ahead of ${SQ}upstream/main${SQ} by 1 commit.
+	  (use "git push" to publish your local commits)
+
+	nothing to commit, working tree clean
+	EOF
+'
+
 test_expect_success 'rename handles remote without fetch refspec' '
 	git clone --bare one no-refspec.git &&
 	# confirm assumption that bare clone does not create refspec
diff --git a/transport.c b/transport.c
index fc144f0aed..30a4ab2cd5 100644
--- a/transport.c
+++ b/transport.c
@@ -1553,8 +1553,11 @@ int transport_push(struct repository *r,
 	if (!(flags & (TRANSPORT_PUSH_DRY_RUN |
 		       TRANSPORT_RECURSE_SUBMODULES_ONLY))) {
 		struct ref *ref;
+		struct remote *tracking_remote = repo_remote_for_push_tracking(
+			r, transport->remote);
+
 		for (ref = remote_refs; ref; ref = ref->next)
-			transport_update_tracking_ref(transport->remote, ref, verbose);
+			transport_update_tracking_ref(tracking_remote, ref, verbose);
 	}
 
 	if (porcelain && !push_ret)
-- 
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