[PATCH v3 1/2] fetch-pack: call prepare_shallow_info only if v0

[Jonathan Tan <jonathantanmy@google.com>]

In fetch_pack(), be clearer that there is no shallow information before
the fetch when v2 is used - memset the struct shallow_info to 0 instead
of calling prepare_shallow_info().

This patch is in preparation for a future patch in which a v2 fetch
might call prepare_shallow_info() after shallow info has been retrieved
during the fetch, so I needed to ensure that prepare_shallow_info() is
not called before the fetch.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
 commit.h     |  4 ++++
 fetch-pack.c | 10 +++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/commit.h b/commit.h
index 42728c2906..a3f2b2eddb 100644
--- a/commit.h
+++ b/commit.h
@@ -257,6 +257,10 @@ extern void setup_alternate_shallow(struct lock_file *shallow_lock,
 extern const char *setup_temporary_shallow(const struct oid_array *extra);
 extern void advertise_shallow_grafts(int);
 
+/*
+ * Initialize with prepare_shallow_info() or zero-initialize (equivalent to
+ * prepare_shallow_info with a NULL oid_array).
+ */
 struct shallow_info {
 	struct oid_array *shallow;
 	int *ours, nr_ours;
diff --git a/fetch-pack.c b/fetch-pack.c
index e69993b2eb..ebb24ada24 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -1648,13 +1648,17 @@ struct ref *fetch_pack(struct fetch_pack_args *args,
 		packet_flush(fd[1]);
 		die(_("no matching remote head"));
 	}
-	prepare_shallow_info(&si, shallow);
-	if (version == protocol_v2)
+	if (version == protocol_v2) {
+		if (shallow->nr)
+			BUG("Protocol V2 does not provide shallows at this point in the fetch");
+		memset(&si, 0, sizeof(si));
 		ref_cpy = do_fetch_pack_v2(args, fd, ref, sought, nr_sought,
 					   pack_lockfile);
-	else
+	} else {
+		prepare_shallow_info(&si, shallow);
 		ref_cpy = do_fetch_pack(args, fd, ref, sought, nr_sought,
 					&si, pack_lockfile);
+	}
 	reprepare_packed_git(the_repository);
 
 	if (!args->cloning && args->deepen) {
-- 
2.21.0.155.ge902e9bcae.dirty