bug#60787: setq-mode-local doesn't work for buffers not visiting files

[Sean Whitton <spwhitton@spwhitton.name>]

Hello,

On Thu 19 Jan 2023 at 08:31AM +02, Eli Zaretskii wrote:

>> Cc: 60787@debbugs.gnu.org
>> From: Sean Whitton <spwhitton@spwhitton.name>
>> Date: Wed, 18 Jan 2023 15:42:42 -0700
>>
>> On Tue 17 Jan 2023 at 09:31AM +02, Juri Linkov wrote:
>>
>> >>   (setq-mode-local diff-mode view-read-only nil)
>> >>
>> >> doesn't affect *vc-diff* buffers, but it should, according to the docstring of
>> >> setq-mode-local.
>> >
>> > Is this because of the condition `(buffer-file-name b)`
>> > in mode-local-map-file-buffers?
>>
>> Yes, but also how setq-mode-local relies on find-file-hook.
>
> All of mode-local.el is written under the assumption that only
> file-visiting buffers are supported.  Evidently, it assumes that modes
> for buffers that don't visit files are "not interesting" enough.  This
> assumption is explicitly in the doc strings of some of its functions.
>
> I don't know why this was the assumption (maybe because CEDET was
> about support of editing program source files?), but if we want to
> lift the restriction, it would require changing many of the functions
> in the package, not just this one.  Maybe we should do that.
> mode-local.el wasn't significantly changed since it was added to Emacs
> as part of CEDET merge, so maybe it's time to extend it?

Sounds good to me.

-- 
Sean Whitton