Merge branch 'en/rev-parse-invalid-range'

"git rev-parse Y..." etc. misbehaved when given endpoints were
not committishes.

* en/rev-parse-invalid-range:
  rev-parse: check lookup'ed commit references for NULL

builtin/rev-parse.c

@@ -282,6 +282,10 @@ static int try_difference(const char *arg)
 			struct commit *a, *b;
 			a = lookup_commit_reference(&start_oid);
 			b = lookup_commit_reference(&end_oid);
+			if (!a || !b) {
+				*dotdot = '.';
+				return 0;
+			}
 			exclude = get_merge_bases(a, b);
 			while (exclude) {
 				struct commit *commit = pop_commit(&exclude);
@@ -328,12 +332,12 @@ static int try_parent_shorthands(const char *arg)
 		return 0;
 
 	*dotdot = 0;
-	if (get_oid_committish(arg, &oid)) {
+	if (get_oid_committish(arg, &oid) ||
+	    !(commit = lookup_commit_reference(&oid))) {
 		*dotdot = '^';
 		return 0;
 	}
 
-	commit = lookup_commit_reference(&oid);
 	if (exclude_parent &&
 	    exclude_parent > commit_list_count(commit->parents)) {
 		*dotdot = '^';

t/t6101-rev-parse-parents.sh

@@ -214,4 +214,12 @@ test_expect_success 'rev-list merge^-1x (garbage after ^-1)' '
 	test_must_fail git rev-list merge^-1x
 '
 
+test_expect_success 'rev-parse $garbage^@ does not segfault' '
+	test_must_fail git rev-parse $EMPTY_TREE^@
+'
+
+test_expect_success 'rev-parse $garbage...$garbage does not segfault' '
+	test_must_fail git rev-parse $EMPTY_TREE...$EMPTY_BLOB
+'
+
 test_done