Re: Add a separate mode for .dir-locals.el

["Clément Pit-Claudel" <cpitclaudel@gmail.com>]

On 2019-10-19 10:14, Eli Zaretskii wrote:
>> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
>> Date: Sat, 19 Oct 2019 08:53:23 -0400
>> Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org
>>
>> Yes, I can describe in more details. [...]
> 
> Thanks, Clément, for your detailed description.  It really makes the
> situation with Flymake crystal clear.

:)

>> My motivation for proposing a separate mode was that we already have a mechanism (atuo-mode-alist) to attach specific behaviors to specific file names, so it seemed natural to reuse that mechanism to run different code for regular ELisp files and dir-locals files.  IOW, I thought it was an anti-pattern to do file-name checks in a major-mode definition.  
> 
> But this part only works for .dir-locals.el files, it will not work
> for any file named otherwise. 

That's true.  I didn't give these files much thought, because (since they don't end in .el) they don't trigger emacs-lisp-mode, and so they are not a problem for Flycheck.

> E.g., my saveplace file is called
> _places.sav (for boring historical reasons), and the only way of using
> such a new mode for it would be to manually turn it on when that file
> is visited.
That's true if we were to introduce a general mode for Lisp data (and, indeed I haven't given such a mode much thought).  If we introduced a mode specifically designed for dir-locals files, on the other hand, it would be turned on automatically for all relevant files (but I see why it's more attractive to look for a solution more general than a dir-locals mode).

> I suggested to collect the traits common to these files, and then
> discuss what would be the appropriate mode for them.  I don't think we
> have now a clear picture of what is or might be needed.  In
> particular, I don't think we have enough data to decide whether
> elisp-mode should support such files as a built-in feature, or there's
> enough differences to justify a separate mode.  In the latter case, we
> will have to devise some way of turning on that new mode automatically
> in most cases.

Understood.  So, for now at least, I will push a patch to Flycheck along the lines of the patch you suggested for Flymake.

Clément.