Merge branch 'sg/ref-filter-wo-repository'

"git ls-remote --sort=<thing>" can feed an object that is not yet
available into the comparison machinery and segfault, which has
been corrected to check such a request upfront and reject it.

* sg/ref-filter-wo-repository:
  ref-filter: don't look for objects when outside of a repository

ref-filter.c

@@ -534,6 +534,10 @@ static int parse_ref_filter_atom(const struct ref_format *format,
 	if (ARRAY_SIZE(valid_atom) <= i)
 		return strbuf_addf_ret(err, -1, _("unknown field name: %.*s"),
 				       (int)(ep-atom), atom);
+	if (valid_atom[i].source != SOURCE_NONE && !have_git_dir())
+		return strbuf_addf_ret(err, -1,
+				       _("not a git repository, but the field '%.*s' requires access to object data"),
+				       (int)(ep-atom), atom);
 	/* Add it in, including the deref prefix */
 	at = used_atom_cnt;

t/t5512-ls-remote.sh

@@ -302,6 +302,12 @@ test_expect_success 'ls-remote works outside repository' '
 	nongit git ls-remote dst.git
 '
+test_expect_success 'ls-remote --sort fails gracefully outside repository' '
+	# Use a sort key that requires access to the referenced objects.
+	nongit test_must_fail git ls-remote --sort=authordate "$TRASH_DIRECTORY" 2>err &&
+	test_i18ngrep "^fatal: not a git repository, but the field '\''authordate'\'' requires access to object data" err
+'
+
 test_expect_success 'ls-remote patterns work with all protocol versions' '
 	git for-each-ref --format="%(objectname)	%(refname)" \
 		refs/heads/master refs/remotes/origin/master >expect &&