Merge branch 'mh/fetch-into-shallow'

"git fetch" into a shallow repository from a repository that does
not know about the shallow boundary commits (e.g. a different fork
from the repository the current shallow repository was cloned from)
did not work correctly.

* 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
-it does not know exists on the server.
+the client's history.
 
 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)) {