bug#50034: 28.0.50; elisp capf error "Wrong type argument: listp, elisp--witness--lisp"

[Lars Ingebrigtsen]

Daniel Mendler <mail@daniel-mendler.de> writes:

> Steps to reproduce:
>
> 1. Start "emacs -Q"
> 2. Enter "(defmacro foo bar" in the scratch buffer
> 3. Press M-<tab> to invoke 'completion-at-point'
>
> The capf will throw the error "Wrong type argument: listp,
> elisp--witness--lisp". This error will be shown on Emacs 27 and Emacs 28.

Slightly simpler repro:

(defmacro foo bar
M-: (elisp--local-variables) RET

It fails here:

                    (`(lambda ,args . ,body)
                     (elisp--local-variables-1
                      (append (remq '&optional (remq '&rest args)) vars)
                      (car (last body))))

where it expects args to be a list, but it's the symbol
`elisp--witness--lisp'.  I'm not quite sure what the correct fix is
here, so I've added Stefan to the CCs.  :-)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no