Merge branch 'mh/fetch-into-shallow' into maint

* mh/fetch-into-shallow:
  t5500: add test for fetching with an unknown 'shallow'
  upload-pack: ignore 'shallow' lines with unknown obj-ids

Documentation/technical/pack-protocol.txt

@@ -228,8 +228,7 @@ obtained through ref discovery.
 The client MUST write all obj-ids which it only has shallow copies
 of (meaning that it does not have the parents of a commit) as
 'shallow' lines so that the server is aware of the limitations of
-the client's history. Clients MUST NOT mention an obj-id which
+the client's history.
-it does not know exists on the server.
 
 The client now sends the maximum commit history depth it wants for
 this transaction, which is the number of commits it wants from the

t/t5500-fetch-pack.sh

@@ -373,6 +373,20 @@ test_expect_success 'clone shallow with packed refs' '
 	test_cmp count8.expected count8.actual
 '
 
+test_expect_success 'fetch in shallow repo unreachable shallow objects' '
+	(
+		git clone --bare --branch B --single-branch "file://$(pwd)/." no-reflog &&
+		git clone --depth 1 "file://$(pwd)/no-reflog" shallow9 &&
+		cd no-reflog &&
+		git tag -d TAGB1 TAGB2 &&
+		git update-ref refs/heads/B B~~ &&
+		git gc --prune=now &&
+		cd ../shallow9 &&
+		git fetch origin &&
+		git fsck --no-dangling
+	)
+'
+
 test_expect_success 'setup tests for the --stdin parameter' '
 	for head in C D E F
 	do

upload-pack.c

@@ -592,7 +592,7 @@ static void receive_needs(void)
 				die("invalid shallow line: %s", line);
 			object = parse_object(sha1);
 			if (!object)
-				die("did not find object for %s", line);
+				continue;
 			if (object->type != OBJ_COMMIT)
 				die("invalid shallow object %s", sha1_to_hex(sha1));
 			if (!(object->flags & CLIENT_SHALLOW)) {