push: heed user.signingkey for signed pushes

push --signed promises to take user.signingkey as the signing key but
fails to read the config.

Make it do so.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/push.c

@@ -471,6 +471,17 @@ static int option_parse_recurse_submodules(const struct option *opt,
 	return 0;
 }
 
+static int git_push_config(const char *k, const char *v, void *cb)
+{
+	struct wt_status *s = cb;
+	int status;
+
+	status = git_gpg_config(k, v, NULL);
+	if (status)
+		return status;
+	return git_default_config(k, v, s);
+}
+
 int cmd_push(int argc, const char **argv, const char *prefix)
 {
 	int flags = 0;
@@ -511,7 +522,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 	};
 
 	packet_trace_identity("push");
-	git_config(git_default_config, NULL);
+	git_config(git_push_config, NULL);
 	argc = parse_options(argc, argv, prefix, options, push_usage, 0);
 
 	if (deleterefs && (tags || (flags & (TRANSPORT_PUSH_ALL | TRANSPORT_PUSH_MIRROR))))

t/t5534-push-signed.sh

@@ -124,4 +124,48 @@ test_expect_success GPG 'signed push sends push certificate' '
 	test_cmp expect dst/push-cert-status
 '
 
+test_expect_success GPG 'fail without key and heed user.signingkey' '
+	prepare_dst &&
+	mkdir -p dst/.git/hooks &&
+	git -C dst config receive.certnonceseed sekrit &&
+	write_script dst/.git/hooks/post-receive <<-\EOF &&
+	# discard the update list
+	cat >/dev/null
+	# record the push certificate
+	if test -n "${GIT_PUSH_CERT-}"
+	then
+		git cat-file blob $GIT_PUSH_CERT >../push-cert
+	fi &&
+
+	cat >../push-cert-status <<E_O_F
+	SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
+	KEY=${GIT_PUSH_CERT_KEY-nokey}
+	STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+	NONCE_STATUS=${GIT_PUSH_CERT_NONCE_STATUS-nononcestatus}
+	NONCE=${GIT_PUSH_CERT_NONCE-nononce}
+	E_O_F
+
+	EOF
+
+	unset GIT_COMMITTER_EMAIL &&
+	git config user.email hasnokey@nowhere.com &&
+	test_must_fail git push --signed dst noop ff +noff &&
+	git config user.signingkey committer@example.com &&
+	git push --signed dst noop ff +noff &&
+
+	(
+		cat <<-\EOF &&
+		SIGNER=C O Mitter <committer@example.com>
+		KEY=13B6F51ECDDE430D
+		STATUS=G
+		NONCE_STATUS=OK
+		EOF
+		sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+	) >expect &&
+
+	grep "$(git rev-parse noop ff) refs/heads/ff" dst/push-cert &&
+	grep "$(git rev-parse noop noff) refs/heads/noff" dst/push-cert &&
+	test_cmp expect dst/push-cert-status
+'
+
 test_done