[PATCH v3 8/8] WIP: receive.allowupdatestohidden

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

This does not work yet, and for a good reason.  As the side that
pushes to a hidden ref never sees that the ref already exists, a
request to update such a ref will come in the form of "please
_create_ this ref and point it at this object", which will not pass
the compare-and-swap based anti-race safety at the receiving end.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/config.txt |  6 ++++++
 builtin/receive-pack.c   |  9 ++++++++-
 t/t5516-fetch-push.sh    | 24 ++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 2dce021..8f13fc0 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1849,6 +1849,12 @@ receive.updateserverinfo::
 	If set to true, git-receive-pack will run git-update-server-info
 	after receiving data from git-push and updating refs.
 
+receive.allowupdatestohidden::
+	When `transfer.hiderefs` is in effect, allow `receive-pack`
+	to accept a push request that asks to update or delete a
+	hidden ref (by default, such a request is rejected).
+	see also `transfer.hiderefs`.
+
 remote.<name>.url::
 	The URL of a remote repository.  See linkgit:git-fetch[1] or
 	linkgit:git-push[1].
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index a8248d9..88500e7 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -41,6 +41,7 @@ static int auto_gc = 1;
 static const char *head_name;
 static void *head_name_to_free;
 static int sent_capabilities;
+static int allow_updates_to_hidden;
 
 static enum deny_action parse_deny_action(const char *var, const char *value)
 {
@@ -119,6 +120,11 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (strcmp(var, "receive.allowupdatestohidden") == 0) {
+		allow_updates_to_hidden = git_config_bool(var, value);
+		return 0;
+	}
+
 	return git_default_config(var, value, cb);
 }
 
@@ -726,7 +732,8 @@ static void execute_commands(struct command *commands, const char *unpacker_erro
 				       0, &cmd))
 		set_connectivity_errors(commands);
 
-	reject_updates_to_hidden(commands);
+	if (!allow_updates_to_hidden)
+		reject_updates_to_hidden(commands);
 
 	if (run_receive_hook(commands, pre_receive_hook, 0)) {
 		for (cmd = commands; cmd; cmd = cmd->next) {
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index 522056f..4c8aef9 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1095,4 +1095,28 @@ test_expect_success 'push to update a hidden ref' '
 	check_push_result $the_first_commit hidden/three
 '
 
+test_expect_failure 'allow push to update a hidden ref' '
+	mk_test heads/master hidden/one hidden/two hidden/three &&
+	(
+		cd testrepo &&
+		git config transfer.hiderefs refs/hidden &&
+		git config receive.allowupdatestohidden yes
+	) &&
+
+	# 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 succeed
+	git push testrepo master:refs/hidden/one &&
+	check_push_result $the_commit heads/master &&
+
+	# push to delete a hidden ref should succeed
+	git push testrepo :refs/hidden/two &&
+	(
+		cd testrepo &&
+		test_must_fail git show-ref -q refs/hidden/one
+	)
+'
+
 test_done
-- 
1.8.1.2.589.ga9b91ac