fetch-pack: do not take shallow lock unnecessarily

When fetching using protocol v2, the remote may send a "shallow-info"
section if the client is shallow. If so, Git as the client currently
takes the shallow file lock, even if the "shallow-info" section is
empty.

This is not a problem except that Git does not support taking the
shallow file lock after modifying the shallow file, because
is_repository_shallow() stores information that is never cleared. And
this take-after-modify occurs when Git does a tag-following fetch from a
shallow repository on a transport that does not support tag following
(since in this case, 2 fetches are performed).

To solve this issue, take the shallow file lock (and perform all other
shallow processing) only if the "shallow-info" section is non-empty;
otherwise, behave as if it were empty.

A full solution (probably, ensuring that any action of committing
shallow file locks also includes clearing the information stored by
is_repository_shallow()) would solve the issue without need for this
patch, but this patch is independently useful (as an optimization to
prevent writing a file in an unnecessary case), hence why I wrote it. I
have included a NEEDSWORK outlining the full solution.

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

1 files changed, 18 insertions, 0 deletions

diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 0f2b09ebb8..fd164d414d 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -471,6 +471,24 @@ test_expect_success 'upload-pack respects client shallows' '
 	grep "fetch< version 2" trace
 '
 
+test_expect_success 'ensure that multiple fetches in same process from a shallow repo works' '
+	rm -rf server client trace &&
+
+	test_create_repo server &&
+	test_commit -C server one &&
+	test_commit -C server two &&
+	test_commit -C server three &&
+	git clone --shallow-exclude two "file://$(pwd)/server" client &&
+
+	git -C server tag -a -m "an annotated tag" twotag two &&
+
+	# Triggers tag following (thus, 2 fetches in one process)
+	GIT_TRACE_PACKET="$(pwd)/trace" git -C client -c protocol.version=2 \
+		fetch --shallow-exclude one origin &&
+	# Ensure that protocol v2 is used
+	grep "fetch< version 2" trace
+'
+
 # Test protocol v2 with 'http://' transport
 #
 . "$TEST_DIRECTORY"/lib-httpd.sh