bug#56400: Make setopt warn on type mismatch

[Lars Ingebrigtsen]

Stefan Kangas <stefan@marxist.se> writes:

> Aha, I guess it doesn't throw an error if `tetris' isn't loaded
> already, as it has no way of knowing the type yet.  IOW, in emacs -Q,
> I need to say this to get an error:
>
> (progn
>   (require 'tetris)
>   (setopt tetris-buffer-width "hello"))

Yup.

> That's pretty good, but I wonder if we could do better.  I expect that
> users will often set settings from libraries that aren't yet loaded.
> For example, how about warning upon loading the library if the
> variable is set to an incompatible value?  Or something.

Hm...  yes, that should certainly be possible.  I guess the check would
go in...  `custom-declare-variable'?  Yeah, almost.

Now fixed in Emacs 29.

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   bloggy blog: http://lars.ingebrigtsen.no