forward-line now works with bignums

* src/cmds.c (Fforward_line): Support bignum arg.
(scan_newline): Return void since no caller was using the
return value.
* src/search.c (find_newline, scan_newline_from_point)
(find_newline1): Return the number of newlines counted, not
the count shortage, so that the return value always fits in
ptrdiff_t even if the original count was a bignum.  All
callers changed.
* test/src/cmds-tests.el (forward-line-with-bignum): New test.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/src/cmds-tests.el b/test/src/cmds-tests.el
index 05c62858773..bab8b5f26ec 100644
--- a/test/src/cmds-tests.el
+++ b/test/src/cmds-tests.el
@@ -30,5 +30,13 @@
   (let ((last-command-event ?a))
     (should-error (self-insert-command -1))))
 
+(ert-deftest forward-line-with-bignum ()
+  (with-temp-buffer
+    (insert "x\n")
+    (let ((shortage (forward-line (1- most-negative-fixnum))))
+      (should (= shortage most-negative-fixnum)))
+    (let ((shortage (forward-line (+ 2 most-positive-fixnum))))
+      (should (= shortage (1+ most-positive-fixnum))))))
+
 (provide 'cmds-tests)
 ;;; cmds-tests.el ends here