Subject: bug#50219: 28.0.50; Provide better errors when trying to specialize on optional args in generic methods

From: Stefan Monnier <[email-masked]>
Date: Sat, 28 Aug 2021 10:15:17 -0400

Eric Abrahamsen [2021-08-26 18:31:44] wrote:
> (cl-defmethod testy ((arg1 string) &optional (arg2 integer))
>   (message "Don't do this"))
[...]
> Warning: reference to free variable 'integer'

Hmm....

The same thing happens in Common-Lisp, tho.  What's going on here is
that the arglist of `cl-defmethod` allows Common-Lisp style arguments
(e.g. `&key`) so your `(arg2 integer)` means to use `integer` as the
default value for `arg2`, just as in

    (cl-defun testy (arg1 &optional (arg2 integer)) ...)

-- Stefan