Mauro Aranda <
maurooaranda@gmail.com> writes:
> Drew Adams <
drew.adams@oracle.com> writes:
>
>>> To sum it up, the prompt is an unfortunate mistake, and maybe we could
>>> protect against that, but I think the real problem comes from the
>>> defcustom, which fails to provide a valid default value.
>>
>> Thanks for this explanation. Makes sense.
>>
>> Can we somehow help users by raising an error when they
>> do this? Seems like a simple mistake to make.
>
> I think it makes sense, but I'm not sure where would be the right place
> to do it.
Coming back to this, perhaps a good place to warn about a bad default
value is where we find it for the first time. So I attach a patch that
makes the restricted-sexp widget warn (but not error out) if the
internal value is not a string.
So, for the defcustom in the recipe:
(defcustom bar
`(ignore)
"..."
:type
'(repeat (restricted-sexp :match-alternatives (functionp)))
:group 'emacs)
When the user clicks the INS button, the following warning pops up:
Warning (widget-bad-default-value):
A widget of type restricted-sexp has a bad default value.
value: nil
match function: widget-restricted-sexp-match
match-alternatives: (functionp)
which I hope conveys good enough information to fix the mistake.
I made it just a warning, because this mistake doesn't always result in
a messed up buffer. But it can be changed to an error, of course.
0001-Warn-about-a-bad-default-value-in-restricted-sexp-wi.patch