[PATCH 7/7] send-pack: support pushing to a shallow clone

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

When send-pack receives "shallow" lines from receive-pack, it knows
the other end does not have a complete commit chains. It restrict
itself to the commits that are not cut out by either end to make sure
the result pack is usuable by receive-pack.

The same technique here, using setup_alternate_shallow() and
--shallow-file, might simplify similar code in upload-pack.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/send-pack.c     |  7 +++++--
 send-pack.c             | 38 +++++++++++++++++++++++++++++++++-----
 send-pack.h             |  4 +++-
 t/t5537-push-shallow.sh | 18 ++++++++++++++++++
 transport.c             |  5 +++--
 5 files changed, 62 insertions(+), 10 deletions(-)

diff --git a/builtin/send-pack.c b/builtin/send-pack.c
index f0ad0ce..b177120 100644
--- a/builtin/send-pack.c
+++ b/builtin/send-pack.c
@@ -94,6 +94,7 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
 	int fd[2];
 	struct child_process *conn;
 	struct extra_have_objects extra_have;
+	struct extra_have_objects shallow;
 	struct ref *remote_refs, *local_refs;
 	int ret;
 	int helper_status = 0;
@@ -206,8 +207,10 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
 	}
 
 	memset(&extra_have, 0, sizeof(extra_have));
+	memset(&shallow, 0, sizeof(shallow));
 
-	get_remote_heads(fd[0], NULL, 0, &remote_refs, REF_NORMAL, &extra_have, NULL);
+	get_remote_heads(fd[0], NULL, 0, &remote_refs, REF_NORMAL,
+			 &extra_have, &shallow);
 
 	transport_verify_remote_names(nr_refspecs, refspecs);
 
@@ -227,7 +230,7 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
 	set_ref_status_for_push(remote_refs, args.send_mirror,
 		args.force_update);
 
-	ret = send_pack(&args, fd, conn, remote_refs, &extra_have);
+	ret = send_pack(&args, fd, conn, remote_refs, &extra_have, &shallow);
 
 	if (helper_status)
 		print_helper_status(remote_refs);
diff --git a/send-pack.c b/send-pack.c
index 81d4b1c..08de681 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -27,14 +27,19 @@ static int feed_object(const unsigned char *sha1, int fd, int negative)
 /*
  * Make a pack stream and spit it out into file descriptor fd
  */
-static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *extra, struct send_pack_args *args)
+static int pack_objects(int fd, struct ref *refs,
+			struct extra_have_objects *extra,
+			struct extra_have_objects *extra_shallow,
+			struct send_pack_args *args)
 {
 	/*
 	 * The child becomes pack-objects --revs; we feed
 	 * the revision parameters to it via its stdin and
 	 * let its stdout go back to the other end.
 	 */
-	const char *argv[] = {
+	const char *av[] = {
+		"--shallow-file",
+		NULL,
 		"pack-objects",
 		"--all-progress-implied",
 		"--revs",
@@ -45,10 +50,27 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 		NULL,
 		NULL,
 	};
+	const char **argv;
 	struct child_process po;
+	static struct lock_file shallow_lock;
+	const char *alternate_shallow_file = NULL;
 	int i;
 
-	i = 4;
+	if (extra_shallow->nr) {
+		memset(&shallow_lock, 0, sizeof(shallow_lock));
+		/* just to load up .git/shallow if exists */
+		is_repository_shallow();
+		setup_alternate_shallow(&shallow_lock,
+					&alternate_shallow_file,
+					extra_shallow,
+					0);
+		av[1] = alternate_shallow_file;
+		argv = av;
+		i = 6;
+	} else {
+		argv = &av[2];
+		i = 4;
+	}
 	if (args->use_thin_pack)
 		argv[i++] = "--thin";
 	if (args->use_ofs_delta)
@@ -100,6 +122,10 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 
 	if (finish_command(&po))
 		return -1;
+
+	if (extra_shallow->nr)
+		rollback_lock_file(&shallow_lock);
+
 	return 0;
 }
 
@@ -176,7 +202,8 @@ static int sideband_demux(int in, int out, void *data)
 int send_pack(struct send_pack_args *args,
 	      int fd[], struct child_process *conn,
 	      struct ref *remote_refs,
-	      struct extra_have_objects *extra_have)
+	      struct extra_have_objects *extra_have,
+	      struct extra_have_objects *extra_shallow)
 {
 	int in = fd[0];
 	int out = fd[1];
@@ -294,7 +321,8 @@ int send_pack(struct send_pack_args *args,
 	}
 
 	if (new_refs && cmds_sent) {
-		if (pack_objects(out, remote_refs, extra_have, args) < 0) {
+		if (pack_objects(out, remote_refs, extra_have, extra_shallow,
+				 args) < 0) {
 			for (ref = remote_refs; ref; ref = ref->next)
 				ref->status = REF_STATUS_NONE;
 			if (args->stateless_rpc)
diff --git a/send-pack.h b/send-pack.h
index 05d7ab1..1c8a343 100644
--- a/send-pack.h
+++ b/send-pack.h
@@ -16,6 +16,8 @@ struct send_pack_args {
 
 int send_pack(struct send_pack_args *args,
 	      int fd[], struct child_process *conn,
-	      struct ref *remote_refs, struct extra_have_objects *extra_have);
+	      struct ref *remote_refs,
+	      struct extra_have_objects *extra_have,
+	      struct extra_have_objects *extra_shallow);
 
 #endif
diff --git a/t/t5537-push-shallow.sh b/t/t5537-push-shallow.sh
index 30fdbc8..76d3d51 100755
--- a/t/t5537-push-shallow.sh
+++ b/t/t5537-push-shallow.sh
@@ -64,4 +64,22 @@ EOF
 	test_cmp expect actual
 '
 
+test_expect_success 'push from shallow to shallow' '
+	(
+	cd shallow &&
+	git push ../shallow2/.git +master:refs/remotes/shallow/master
+	) &&
+	(
+	cd shallow2 &&
+	git log --format=%s shallow/master >actual &&
+	git fsck &&
+	cat <<EOF >expect &&
+5
+4
+3
+EOF
+	test_cmp expect actual
+	)
+'
+
 test_done
diff --git a/transport.c b/transport.c
index 17fef16..d592e8d 100644
--- a/transport.c
+++ b/transport.c
@@ -802,7 +802,8 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 		struct ref *tmp_refs;
 		connect_setup(transport, 1, 0);
 
-		get_remote_heads(data->fd[0], NULL, 0, &tmp_refs, REF_NORMAL, NULL, NULL);
+		get_remote_heads(data->fd[0], NULL, 0, &tmp_refs, REF_NORMAL,
+				 NULL, &data->shallow);
 		data->got_remote_heads = 1;
 	}
 
@@ -817,7 +818,7 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 	args.porcelain = !!(flags & TRANSPORT_PUSH_PORCELAIN);
 
 	ret = send_pack(&args, data->fd, data->conn, remote_refs,
-			&data->extra_have);
+			&data->extra_have, &data->shallow);
 
 	close(data->fd[1]);
 	close(data->fd[0]);
-- 
1.8.2.83.gc99314b