upload/receive-pack: allow hiding ref hierarchies

A repository may have refs that are only used for its internal
bookkeeping purposes that should not be exposed to the others that
come over the network.

Teach upload-pack to omit some refs from its initial advertisement
by paying attention to the uploadpack.hiderefs multi-valued
configuration variable.  Do the same to receive-pack via the
receive.hiderefs variable.  As a convenient short-hand, allow using
transfer.hiderefs to set the value to both of these variables.

Any ref that is under the hierarchies listed on the value of these
variable is excluded from responses to requests made by "ls-remote",
"fetch", etc. (for upload-pack) and "push" (for receive-pack).

Because these hidden refs do not count as OUR_REF, an attempt to
fetch objects at the tip of them will be rejected, and because these
refs do not get advertised, "git push :" will not see local branches
that have the same name as them as "matching" ones to be sent.

An attempt to update/delete these hidden refs with an explicit
refspec, e.g. "git push origin :refs/hidden/22", is rejected.  This
is not a new restriction.  To the pusher, it would appear that there
is no such ref, so its push request will conclude with "Now that I
sent you all the data, it is time for you to update the refs.  I saw
that the ref did not exist when I started pushing, and I want the
result to point at this commit".  The receiving end will apply the
compare-and-swap rule to this request and rejects the push with
"Well, your update request conflicts with somebody else; I see there
is such a ref.", which is the right thing to do. Otherwise a push to
a hidden ref will always be "the last one wins", which is not a good
default.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 39 insertions, 0 deletions

diff --git a/t/t5512-ls-remote.sh b/t/t5512-ls-remote.sh
index d16e5d384..321c3e523 100755
--- a/t/t5512-ls-remote.sh
+++ b/t/t5512-ls-remote.sh
@@ -126,4 +126,16 @@ test_expect_success 'Report match with --exit-code' '
 	test_cmp expect actual
 '
 
+for configsection in transfer uploadpack
+do
+	test_expect_success "Hide some refs with $configsection.hiderefs" '
+		test_config $configsection.hiderefs refs/tags &&
+		git ls-remote . >actual &&
+		test_unconfig $configsection.hiderefs &&
+		git ls-remote . |
+		sed -e "/	refs\/tags\//d" >expect &&
+		test_cmp expect actual
+	'
+done
+
 test_done
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index 60093728f..2b26ecebf 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1037,4 +1037,31 @@ test_expect_success 'push --prune refspec' '
 	! check_push_result $the_first_commit tmp/foo tmp/bar
 '
 
+for configsection in transfer receive
+do
+	test_expect_success "push to update a ref hidden by $configsection.hiderefs" '
+		mk_test heads/master hidden/one hidden/two hidden/three &&
+		(
+			cd testrepo &&
+			git config $configsection.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 :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
+	'
+done
+
 test_done