[PATCH v2 3/3] receive-pack: reject an attempt to update/delete a hidden ref

[Junio C Hamano <gitster@pobox.com>]

An attempt to update or delete a ref that is hidden from "git push"
is rejected.  With this the server side can implement refs that are
only available for its own use, e.g. refs/pull/11/head used to hold
an incoming pull request at GitHub.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/config.txt |  3 ++-
 builtin/receive-pack.c   | 16 ++++++++++++++++
 t/t5516-fetch-push.sh    | 24 ++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 8e2853e..b7b407b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2063,7 +2063,8 @@ transfer.hiderefs::
 	more than one transfer.hiderefs configuration variables to
 	specify multiple prefix strings. A ref that has one of these
 	strings as its prefix is excluded, and is hidden from
-	`git clone --mirror` and `git push :`.
+	`git clone --mirror` and `git push :`.  An attempt to update
+	or delete a hidden ref by `git push` is	rejected.
 
 transfer.unpackLimit::
 	When `fetch.unpackLimit` or `receive.unpackLimit` are
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 5ed40be..a8248d9 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -696,6 +696,20 @@ static int iterate_receive_command_list(void *cb_data, unsigned char sha1[20])
 	return -1; /* end of list */
 }
 
+static void reject_updates_to_hidden(struct command *commands)
+{
+	struct command *cmd;
+
+	for (cmd = commands; cmd; cmd = cmd->next) {
+		if (cmd->error_string || !ref_is_hidden(cmd->ref_name))
+			continue;
+		if (is_null_sha1(cmd->new_sha1))
+			cmd->error_string = "deny deleting a hidden ref";
+		else
+			cmd->error_string = "deny updating a hidden ref";
+	}
+}
+
 static void execute_commands(struct command *commands, const char *unpacker_error)
 {
 	struct command *cmd;
@@ -712,6 +726,8 @@ static void execute_commands(struct command *commands, const char *unpacker_erro
 				       0, &cmd))
 		set_connectivity_errors(commands);
 
+	reject_updates_to_hidden(commands);
+
 	if (run_receive_hook(commands, pre_receive_hook, 0)) {
 		for (cmd = commands; cmd; cmd = cmd->next) {
 			if (!cmd->error_string)
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index 6009372..8e8287a 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1037,4 +1037,28 @@ test_expect_success 'push --prune refspec' '
 	! check_push_result $the_first_commit tmp/foo tmp/bar
 '
 
+test_expect_success 'push to update a hidden ref' '
+	mk_test heads/master hidden/one hidden/two hidden/three &&
+	(
+		cd testrepo &&
+		git config transfer.hiderefs refs/hidden
+	) &&
+
+	# push to unhidden ref succeeds normally
+	git push testrepo master:refs/heads/master &&
+	check_push_result $the_commit heads/master &&
+
+	# push to update a hidden ref should fail
+	test_must_fail git push testrepo master:refs/hidden/one &&
+	check_push_result $the_first_commit hidden/one &&
+
+	# push to delete a hidden ref should fail
+	test_must_fail git push testrepo master:refs/hidden/two &&
+	check_push_result $the_first_commit hidden/two &&
+
+	# idempotent push to update a hidden ref should fail
+	test_must_fail git push testrepo $the_first_commit:refs/hidden/three &&
+	check_push_result $the_first_commit hidden/three
+'
+
 test_done
-- 
1.8.1.2.548.g0e4986f