GNU bug report logs - #22847
#17062: 24.3 current-fill-column breaks fill-match-adaptive-prefix

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From: Stefan Kangas <stefan <at> marxist.se>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 22847 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: bug#22847: #17062: 24.3 current-fill-column breaks fill-match-adaptive-prefix
Date: Fri, 14 Aug 2020 22:14:09 -0700

[Message part 1 (text/plain, inline)]

tags 22847 + patch
thanks

Glenn Morris <rgm <at> gnu.org> writes:

> Eli Zaretskii wrote:
>
>>> TLDR:
>>> Let's remove the test for nil fill-column in current-fill-column.
>>
>> I don't understand what you propose to do instead.
>> current-fill-column does arithmetics on fill-column when it's non-nil,
>> so we cannot just remove the test, because the function will then
>> signal an error.
>
> Yes, I'm fine with the error.
>
>> I see 3 possible ways to fix these bugs:
>>
>>   . Fix the code which is not prepared for fill-column being nil to be
>>     prepared.  This leaves everyone happy, except, perhaps, the person
>>     who would need to fix all those places in Emacs.
>
> I think this would be a waste of time for the Emacs, and third party,
> maintainers.

Agreed.

>>   . Change current-fill-column to return most-positive-fixnum when
>>     fill-column is nil.
>
> I suppose this would be ok, so long as it comes with something like a
> once-per session display-warning about this being an obsolete usage that
> will be removed soon.

I've attached a proposed patch which does that here.

>>   . Disallow fill-column being nil and remove the test from
>>     current-fill-column without changing anything else, i.e. let it
>>     signal an error, perhaps with some text that tells this value is
>>     no longer supported.  This will break setups of those who use that
>>     value to disable auto-fill, something that was available since
>>     forever, so I don't think we can do that.
>
> That's what I would do. I don't have a problem breaking an undocumented
> feature that already fails in several places, and has a trivial
> workaround (don't want auto-fill - don't turn it on). Other times I can
> recall similar breakage happening: byte-compile of nil, setq with odd
> number of arguments. People gripe for a bit, then get on with life.

I'm perfectly fine with this solution as well, if we prefer that.

Thoughts?

Best regards,
Stefan Kangas

[0001-Make-nil-value-of-fill-column-obsolete.patch (text/x-diff, attachment)]

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