Teach git-fetch to exploit server side automatic tag following

If the remote peer upload-pack process supports the include-tag
protocol extension then we can avoid running a second fetch cycle
on the client side by letting the server send us the annotated tags
along with the objects it is packing for us.  In the following graph
we can now fetch both "tag1" and "tag2" on the same connection that
we fetched "master" from the remote when we only have L available
on the local side:

         T - tag1          S - tag2
        /                 /
   L - o ------ o ------ B
    \                     \
     \                     \
      origin/master         master

The objects for "tag1" are implicitly downloaded without our direct
knowledge.  The existing "quickfetch" optimization within git-fetch
discovers that tag1 is complete after the first connection and does
not open a second connection.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/transport.c b/transport.c
index 166c1d1d46..393e0e8fe2 100644
--- a/transport.c
+++ b/transport.c
@@ -560,6 +560,7 @@ static int close_bundle(struct transport *transport)
 struct git_transport_data {
 	unsigned thin : 1;
 	unsigned keep : 1;
+	unsigned followtags : 1;
 	int depth;
 	struct child_process *conn;
 	int fd[2];
@@ -580,6 +581,9 @@ static int set_git_option(struct transport *connection,
 	} else if (!strcmp(name, TRANS_OPT_THIN)) {
 		data->thin = !!value;
 		return 0;
+	} else if (!strcmp(name, TRANS_OPT_FOLLOWTAGS)) {
+		data->followtags = !!value;
+		return 0;
 	} else if (!strcmp(name, TRANS_OPT_KEEP)) {
 		data->keep = !!value;
 		return 0;
@@ -628,6 +632,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 	args.keep_pack = data->keep;
 	args.lock_pack = 1;
 	args.use_thin_pack = data->thin;
+	args.include_tag = data->followtags;
 	args.verbose = transport->verbose > 0;
 	args.depth = data->depth;