send-pack: fix push nego. when remote has refs

Commit 477673d6f3 ("send-pack: support push negotiation", 2021-05-05)
did not test the case in which a remote advertises at least one ref. In
such a case, "remote_refs" in get_commons_through_negotiation() in
send-pack.c would also contain those refs with a zero ref->new_oid (in
addition to the refs being pushed with a nonzero ref->new_oid). Passing
them as negotiation tips to "git fetch" causes an error, so filter them
out.

(The exact error that would happen in "git fetch" in this case is a
segmentation fault, which is unwanted. This will be fixed in the
subsequent commit.)

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

send-pack.c

@@ -425,8 +425,10 @@ static void get_commons_through_negotiation(const char *url,
 	child.no_stdin = 1;
 	child.out = -1;
 	strvec_pushl(&child.args, "fetch", "--negotiate-only", NULL);
-	for (ref = remote_refs; ref; ref = ref->next)
-		strvec_pushf(&child.args, "--negotiation-tip=%s", oid_to_hex(&ref->new_oid));
+	for (ref = remote_refs; ref; ref = ref->next) {
+		if (!is_null_oid(&ref->new_oid))
+			strvec_pushf(&child.args, "--negotiation-tip=%s", oid_to_hex(&ref->new_oid));
+	}
 	strvec_push(&child.args, url);
 
 	if (start_command(&child))

t/t5516-fetch-push.sh

@@ -201,6 +201,7 @@ test_expect_success 'push with negotiation' '
 	# Without negotiation
 	mk_empty testrepo &&
 	git push testrepo $the_first_commit:refs/remotes/origin/first_commit &&
+	test_commit -C testrepo unrelated_commit &&
 	git -C testrepo config receive.hideRefs refs/remotes/origin/first_commit &&
 	echo now pushing without negotiation &&
 	GIT_TRACE2_EVENT="$(pwd)/event" git -c protocol.version=2 push testrepo refs/heads/main:refs/remotes/origin/main &&
@@ -210,6 +211,7 @@ test_expect_success 'push with negotiation' '
 	rm event &&
 	mk_empty testrepo &&
 	git push testrepo $the_first_commit:refs/remotes/origin/first_commit &&
+	test_commit -C testrepo unrelated_commit &&
 	git -C testrepo config receive.hideRefs refs/remotes/origin/first_commit &&
 	GIT_TRACE2_EVENT="$(pwd)/event" git -c protocol.version=2 -c push.negotiate=1 push testrepo refs/heads/main:refs/remotes/origin/main &&
 	grep_wrote 2 event # 1 commit, 1 tree
@@ -219,6 +221,7 @@ test_expect_success 'push with negotiation proceeds anyway even if negotiation f
 	rm event &&
 	mk_empty testrepo &&
 	git push testrepo $the_first_commit:refs/remotes/origin/first_commit &&
+	test_commit -C testrepo unrelated_commit &&
 	git -C testrepo config receive.hideRefs refs/remotes/origin/first_commit &&
 	GIT_TEST_PROTOCOL_VERSION=0 GIT_TRACE2_EVENT="$(pwd)/event" \
 		git -c push.negotiate=1 push testrepo refs/heads/main:refs/remotes/origin/main 2>err &&
@@ -1767,5 +1770,4 @@ test_expect_success 'denyCurrentBranch and worktrees' '
 	git -C cloned push origin HEAD:new-wt &&
 	test_must_fail git -C cloned push --delete origin new-wt
 '
-
 test_done

t/t5549-fetch-push-http.sh

@@ -27,6 +27,7 @@ setup_client_and_server () {
 	git init "$SERVER" &&
 	test_when_finished 'rm -rf "$SERVER"' &&
 	test_config -C "$SERVER" http.receivepack true &&
+	test_commit -C "$SERVER" unrelated_commit &&
 	git -C client push "$URI" first_commit:refs/remotes/origin/first_commit &&
 	git -C "$SERVER" config receive.hideRefs refs/remotes/origin/first_commit
 }