Mention new strictness for &optional, &rest in arglists (Bug#29165)

* etc/NEWS: Explain that '&optional' not followed by a variable is now
an error.
* lisp/emacs-lisp/cl-macs.el (cl--transform-lambda, cl--do-&aux)
(cl--do-arglist): Also reject '&optional', '&rest', or '&aux' not
followed by a variable for consistency.
* test/lisp/emacs-lisp/cl-macs-tests.el (cl-macs-bad-arglist): New
test.

1 files changed, 11 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 64b53d88c83..5324a0944ea 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1462,6 +1462,17 @@ them through 'format' first.  Even that is discouraged: for ElDoc
 support, you should set 'eldoc-documentation-function' instead of
 calling 'eldoc-message' directly.
 
+---
+** Using '&rest' or '&optional' incorrectly is now an error.
+For example giving '&optional' without a following variable, or
+passing '&optional' multiple times:
+
+    (defun foo (&optional &rest x))
+    (defun bar (&optional &optional x))
+
+Previously, Emacs would just ignore the extra keyword, or give
+incorrect results in certain cases.
+
 
 * Lisp Changes in Emacs 26.1