bug#68931: 30.0.50; Gnus byte-compilation error with (display . [not expire]) with git emacs

[Eric Abrahamsen]

Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs@gnu.org> writes:

>> For my information: the problem here is that
>> `gnus-category-make-function' runs `gnus-byte-compile' on a form like
>> this:
>
> BTW, `gnus-category-make-function` is a misnomer since it does not
> return a function.

I'll add a FIXME...

>> (lambda nil (not (#f(compiled-function () #<bytecode 0x1980ad44c232>))))
>>
>> And the extra parens around (#f(compiled-function...)) are not strictly 
>> legal?
>
> A Lisp function call has the form (FUN . ARGS) where FUN is not expected
> to be a function *value* but rather should be a function name (and we
> also tolerate a lambda expression, which is a function's source code).

Thanks! I guess I never understood that explicitly.

> The patch below should fix the core of the problem, but it probably
> requires corresponding adjustments in `gnus-function-implies-unread-1`
> and `gnus-category-make-function`.

I'll try this out, and see what's necessary to make it work.

In general I think Gnus goes to a lot of this kind of effort, based on
performance considerations that are no longer current. Especially with
native compilation available, I suspect there's no real need to keep
byte-compiling things on the fly.

>
>         Stefan
>
>
> diff --git a/lisp/gnus/gnus-agent.el b/lisp/gnus/gnus-agent.el
> index 604eea4c33d..cfcbea2e233 100644
> --- a/lisp/gnus/gnus-agent.el
> +++ b/lisp/gnus/gnus-agent.el
> @@ -2911,13 +2911,9 @@
>       (car func)
>        (gnus-byte-compile `(lambda () ,func)))))
>  
> -(defun gnus-agent-true ()
> -  "Return t."
> -  t)
> +(defalias 'gnus-agent-true #'always)
>  
> -(defun gnus-agent-false ()
> -  "Return nil."
> -  nil)
> +(defalias 'gnus-agent-false #'ignore)
>  
>  (defun gnus-category-make-function-1 (predicate)
>    "Make a function from PREDICATE."
> @@ -2925,8 +2921,9 @@ gnus-category-make-function-1
>     ;; Functions are just returned as is.
>     ((or (symbolp predicate)
>       (functionp predicate))
> -    `(,(or (cdr (assq predicate gnus-category-predicate-alist))
> -        predicate)))
> +    (let ((fun (or (cdr (assq predicate gnus-category-predicate-alist))
> +                predicate)))
> +      (if (symbolp fun) `(,fun) `(funcall ',fun))))
>     ;; More complex predicate.
>     ((consp predicate)
>      `(,(cond