fetch-pack: objects in our alternates are available to us

Use the helper function split from the receiving end of "git push" to
allow the same optimization on the receiving end of "git fetch".

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

builtin/fetch-pack.c

@@ -9,6 +9,7 @@
 #include "fetch-pack.h"
 #include "remote.h"
 #include "run-command.h"
+#include "transport.h"
 
 static int transfer_unpack_limit = -1;
 static int fetch_unpack_limit = -1;
@@ -217,6 +218,16 @@ static void send_request(int fd, struct strbuf *buf)
 		safe_write(fd, buf->buf, buf->len);
 }
 
+static void insert_one_alternate_ref(const struct ref *ref, void *unused)
+{
+	rev_list_insert_ref(NULL, ref->old_sha1, 0, NULL);
+}
+
+static void insert_alternate_refs(void)
+{
+	foreach_alt_odb(refs_from_alternate_cb, insert_one_alternate_ref);
+}
+
 static int find_common(int fd[2], unsigned char *result_sha1,
 		       struct ref *refs)
 {
@@ -235,6 +246,7 @@ static int find_common(int fd[2], unsigned char *result_sha1,
 	marked = 1;
 
 	for_each_ref(rev_list_insert_ref, NULL);
+	insert_alternate_refs();
 
 	fetching = 0;
 	for ( ; refs ; refs = refs->next) {

t/t5501-fetch-push-alternates.sh

@@ -54,7 +54,7 @@ test_expect_success 'pushing into a repository with the same alternate' '
 	test_cmp one.count receiver.count
 '
 
-test_expect_failure 'fetching from a repository with the same alternate' '
+test_expect_success 'fetching from a repository with the same alternate' '
 	(
 		cd fetcher &&
 		git fetch ../one master:refs/heads/it &&