fast-export: Omit tags that tag trees

Commit c0582c53bc introduced logic to just
omit tags that point to tree objects.  However, these objects were still
being output and were pointing at "mark :0", which caused fast-import to
crash.  This patch makes sure such tags (including deeper nestings such
as tags of tags of trees), are omitted.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-fast-export.c

@@ -289,6 +289,21 @@ static void handle_tag(const char *name, struct tag *tag)
 	char *buf;
 	const char *tagger, *tagger_end, *message;
 	size_t message_size = 0;
+	struct object *tagged;
+
+	/* Trees have no identifer in fast-export output, thus we have no way
+	 * to output tags of trees, tags of tags of trees, etc.  Simply omit
+	 * such tags.
+	 */
+	tagged = tag->tagged;
+	while (tagged->type == OBJ_TAG) {
+		tagged = ((struct tag *)tagged)->tagged;
+	}
+	if (tagged->type == OBJ_TREE) {
+		warning("Omitting tag %s,\nsince tags of trees (or tags of tags of trees, etc.) are not supported.",
+			sha1_to_hex(tag->object.sha1));
+		return;
+	}
 
 	buf = read_sha1_file(tag->object.sha1, &type, &size);
 	if (!buf)

t/t9301-fast-export.sh

@@ -271,8 +271,14 @@ test_expect_success 'set-up a few more tags for tag export tests' '
 	git tag -a tag-obj_tag-obj -m "tagging a tag" tree_tag-obj
 '
 
+test_expect_success 'tree_tag'        '
+	mkdir result &&
+	(cd result && git init) &&
+	git fast-export tree_tag > fe-stream &&
+	(cd result && git fast-import < ../fe-stream)
+'
+
 # NEEDSWORK: not just check return status, but validate the output
-test_expect_success 'tree_tag'        'git fast-export tree_tag'
 test_expect_success 'tree_tag-obj'    'git fast-export tree_tag-obj'
 test_expect_success 'tag-obj_tag'     'git fast-export tag-obj_tag'
 test_expect_success 'tag-obj_tag-obj' 'git fast-export tag-obj_tag-obj'