Re: master d08c947: Make compilation-mode regexp matching case-sensitive (bug#40119)

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> The regular expressions are written either with or without case-folding
>> in mind, so changing it globally is a recipe for problems.
> Agreed, but I doubt that anyone will ever set the option.

Then let's make it into a simple `defvar` rather than a defcustom and
make the docstring clarify that it's only useful for temporary
backward compatibility.

>> PS: The same applies to the "zero/one-based column numbers" and
>>    the "char-colums vs visual-columns vs byte-columns", admittedly.
>
> Yes, those settings would make more sense if they were rule-specific.
> Still, actual examples of tools needing them would be useful.

In sml-mode.el (GNU ELPA) I set `compilation-error-screen-columns`
buffer-locally but it really should be rule-local.  In tuareg-mode (not
in GNU ELPA, sadly), I set both `compilation-first-column` and
`compilation-error-screen-columns` buffer-locally for the same reason.


        Stefan