fetch: pass ref prefixes when fetching

Construct a list of ref prefixes to be passed to
'transport_get_remote_refs()' from the refspec to be used during the
fetch.  This list of ref prefixes will be used to allow the server to
filter the ref advertisement when communicating using protocol v2.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -332,11 +332,28 @@ static struct ref *get_ref_map(struct transport *transport,
 	struct ref *rm;
 	struct ref *ref_map = NULL;
 	struct ref **tail = &ref_map;
+	struct argv_array ref_prefixes = ARGV_ARRAY_INIT;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
 
-	const struct ref *remote_refs = transport_get_remote_refs(transport, NULL);
+	const struct ref *remote_refs;
+
+	for (i = 0; i < refspec_count; i++) {
+		if (!refspecs[i].exact_sha1) {
+			const char *glob = strchr(refspecs[i].src, '*');
+			if (glob)
+				argv_array_pushf(&ref_prefixes, "%.*s",
+						 (int)(glob - refspecs[i].src),
+						 refspecs[i].src);
+			else
+				expand_ref_prefix(&ref_prefixes, refspecs[i].src);
+		}
+	}
+
+	remote_refs = transport_get_remote_refs(transport, &ref_prefixes);
+
+	argv_array_clear(&ref_prefixes);
 
 	if (refspec_count) {
 		struct refspec *fetch_refspec;