[PATCH v2 3/3] Teach git-fetch to exploit server side automatic tag following

["Shawn O. Pearce" <spearce@spearce.org>]

If the remote peer upload-pack process supports the auto-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>
---
 builtin-fetch.c      |    3 +++
 t/t5503-tagfollow.sh |   26 ++++++++++++++++++++++++++
 transport.c          |    5 +++++
 transport.h          |    3 +++
 4 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/builtin-fetch.c b/builtin-fetch.c
index 26c3d74..55f611e 100644
--- a/builtin-fetch.c
+++ b/builtin-fetch.c
@@ -555,6 +555,8 @@ static int do_fetch(struct transport *transport,
 			read_ref(rm->peer_ref->name, rm->peer_ref->old_sha1);
 	}
 
+	if (tags == TAGS_DEFAULT && autotags)
+		transport_set_option(transport, TRANS_OPT_FOLLOWTAGS, "1");
 	if (fetch_refs(transport, ref_map)) {
 		free_refs(ref_map);
 		return 1;
@@ -568,6 +570,7 @@ static int do_fetch(struct transport *transport,
 		ref_map = NULL;
 		find_non_local_tags(transport, &ref_map, &tail);
 		if (ref_map) {
+			transport_set_option(transport, TRANS_OPT_FOLLOWTAGS, NULL);
 			transport_set_option(transport, TRANS_OPT_DEPTH, "0");
 			fetch_refs(transport, ref_map);
 		}
diff --git a/t/t5503-tagfollow.sh b/t/t5503-tagfollow.sh
index 45ff982..86e5b9b 100755
--- a/t/t5503-tagfollow.sh
+++ b/t/t5503-tagfollow.sh
@@ -121,4 +121,30 @@ test_expect_success 'fetch B, S (commit and tag : 1 connection)' '
 	git diff expect actual
 '
 
+cat - <<EOF >expect
+#S
+want $B
+want $S
+#E
+EOF
+test_expect_success 'new clone fetch master and tags' '
+	git branch -D cat
+	rm -f $U
+	(
+		mkdir clone2 &&
+		cd clone2 &&
+		git init &&
+		git remote add origin .. &&
+		GIT_DEBUG_SEND_PACK=3 git fetch 3>../$U &&
+		test $B = $(git rev-parse --verify origin/master) &&
+		test $S = $(git rev-parse --verify tag2) &&
+		test $B = $(git rev-parse --verify tag2^0) &&
+		test $T = $(git rev-parse --verify tag1) &&
+		test $A = $(git rev-parse --verify tag1^0)
+	) &&
+	test -s $U &&
+	cut -d" " -f1,2 $U >actual &&
+	git diff expect actual
+'
+
 test_done
diff --git a/transport.c b/transport.c
index 166c1d1..12873db 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.auto_include_tag = data->followtags;
 	args.verbose = transport->verbose > 0;
 	args.depth = data->depth;
 
diff --git a/transport.h b/transport.h
index 6fb4526..8abfc0a 100644
--- a/transport.h
+++ b/transport.h
@@ -53,6 +53,9 @@ struct transport *transport_get(struct remote *, const char *);
 /* Limit the depth of the fetch if not null */
 #define TRANS_OPT_DEPTH "depth"
 
+/* Aggressively fetch annotated tags if possible */
+#define TRANS_OPT_FOLLOWTAGS "followtags"
+
 /**
  * Returns 0 if the option was used, non-zero otherwise. Prints a
  * message to stderr if the option is not used.
-- 
1.5.4.3.529.gb25fb