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

[Eli Zaretskii]

> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Mon, 5 Feb 2024 15:00:36 +0100
> Cc: Dan Christensen <jdc@uwo.ca>,
>  68931@debbugs.gnu.org,
>  Stefan Monnier <monnier@iro.umontreal.ca>
> 
> >> Debugger entered--returning value: "Malformed function ‘#[0 
> >> \"\\301\\300!\\207\" [expire gnus-article-marked-p] 2]’"
> ...
> >> * gnus-summary-display-make-predicate((not expire))
> 
> Apparently, gnus-category-make-function-1 creates code that isn't really 
> valid Lisp but that we have previously allowed anyway: (F ...) where F is a 
> (non-symbol) function value, instead of using `funcall`.
> 
> We could (and probably should) allow this for compatibility but perhaps it's 
> time to at least start warning about it? It makes the quirky semantics of a 
> Lisp-2 even quirkier.

I think the offending function should be fixed not to produce invalid
code, rather than support such code.