dir-local vs major-mode setting

dir-local vs major-mode setting

[Stefan Monnier]

If we have a dir-locals.el that says:

    ((nil . ((indent-tabs-mode . t))))

I think it would make sense to give this setting "lower priority" than
the setting of indent-tabs-mode that might be imposed by the major mode.

I.e. maybe it should be applied in kill-all-local-variables rather than
at the end of the major mode setup.

WDYT?


        Stefan

Re: dir-local vs major-mode setting

[Phil Sainty]

On 2018-11-15 07:30, Stefan Monnier wrote:
> If we have a dir-locals.el that says:
> 
>     ((nil . ((indent-tabs-mode . t))))
> 
> I think it would make sense to give this setting "lower priority"
> than the setting of indent-tabs-mode that might be imposed by the
> major mode.

The current priority order is sensible to me.

I use the major mode hooks to set my preferred behaviour for each
mode, and dir-local settings to override them in cases where I should
*not* be using the defaults (e.g. to enforce a particular project's
coding standards).


-Phil

Re: dir-local vs major-mode setting

[Stefan Monnier]

> I use the major mode hooks to set my preferred behaviour for each
> mode, and dir-local settings to override them in cases where I should
> *not* be using the defaults (e.g. to enforce a particular project's
> coding standards).

I'm thinking of a case where the project says "you should use TABs" so
it sets

    ((nil . ((indent-tabs-mode . t))))

in the .dir-locals.el file.  But TABs in TeX files tend to behave funny,
so tex-mode.el sets indent-tabs-mode to nil.  Assuming the
.dir-locals.el setting was meant for "the majority of the files" and
those aren't .tex files, it would make sense to favor the major
mode's setting for the few .tex files.

I guess sometimes you want one and sometimes you want the other.
So maybe to handle that case we'd want to introduce another wildcard
that works like the `nil` above but implies it's applied before running
the major mode's setup function.


        Stefan

Re: dir-local vs major-mode setting

[Phil Sainty]

On 2018-11-15 11:19, Stefan Monnier wrote:
> I'm thinking of a case where the project says "you should use TABs" so
> it sets
> 
>     ((nil . ((indent-tabs-mode . t))))
> 
> in the .dir-locals.el file.  But TABs in TeX files tend to behave
> funny, so tex-mode.el sets indent-tabs-mode to nil.  Assuming the
> .dir-locals.el setting was meant for "the majority of the files"
> and those aren't .tex files, it would make sense to favor the major
> mode's setting for the few .tex files.

If the project is expected to contain .tex files then the above would
constitute a bug in the .dir-locals.el file (which should contain mode-
specific entries for exceptions to the global settings).

Users could either fix the .dir-locals.el file, or add their own
custom .dir-locals-2.el file with the necessary overrides.

They can also use `hack-local-variables-hook'.


> I guess sometimes you want one and sometimes you want the other.
> So maybe to handle that case we'd want to introduce another wildcard
> that works like the `nil` above but implies it's applied before running
> the major mode's setup function.

If a "hack certain local vars before running hooks" facility was added,
I wouldn't think it should be constrained to the nil case?

Perhaps add something like the string path syntax, under which you
can provide a complete dir-locals spec, which should run early.  The
key might be a keyword like :early or some such.


-Phil

Re: dir-local vs major-mode setting

[Stefan Monnier]

> If the project is expected to contain .tex files then the above would
> constitute a bug in the .dir-locals.el file (which should contain mode-
> specific entries for exceptions to the global settings).

The whole point of `nil` is that it's not mode-specific.

>> I guess sometimes you want one and sometimes you want the other.
>> So maybe to handle that case we'd want to introduce another wildcard
>> that works like the `nil` above but implies it's applied before running
>> the major mode's setup function.
> If a "hack certain local vars before running hooks" facility was added,
> I wouldn't think it should be constrained to the nil case?

For the non-nil case, the need is much less severe: for any given major
mode, in 99% of the cases, an early setting will either have no effect
or have the same effect as a late setting.

This said, for parent major modes (e.g. prog-mode, text-mode), it can
still be useful in more than 1% of the cases, indeed.


        Stefan

Re: dir-local vs major-mode setting

[Phil Sainty]

On 2018-11-15 16:00, Stefan Monnier wrote:
>> If the project is expected to contain .tex files then the above would
>> constitute a bug in the .dir-locals.el file (which should contain 
>> mode-
>> specific entries for exceptions to the global settings).
> 
> The whole point of `nil` is that it's not mode-specific.

Sorry, I shouldn't have said "global" there; that was confusing.
I was referring to the nil case.

i.e. I would expect the .dir-locals.el to have, say:

((nil . ((indent-tabs-mode . t)))
  (tex-mode . ((indent-tabs-mode . nil))))

So that tex-mode files don't use tabs, but other modes will.

However, I've also just noticed that Emacs 26.1 appears to have broken/
inverted the way that such overrides work.

https://emacs.stackexchange.com/a/46005/454


-Phil

Re: dir-local vs major-mode setting

[Stefan Monnier]

>>> If the project is expected to contain .tex files then the above would
>>> constitute a bug in the .dir-locals.el file (which should contain mode-
>>> specific entries for exceptions to the global settings).
>>
>> The whole point of `nil` is that it's not mode-specific.
>
> Sorry, I shouldn't have said "global" there; that was confusing.
> I was referring to the nil case.
>
> i.e. I would expect the .dir-locals.el to have, say:
>
> ((nil . ((indent-tabs-mode . t)))
>  (tex-mode . ((indent-tabs-mode . nil))))
>
> So that tex-mode files don't use tabs, but other modes will.

But having to add

    (tex-mode . ((indent-tabs-mode . nil)))

when the major mode normally does it for you is kind of a let-down.

IOW, I think .dir-locals.el should offer some way to say "for files in
this directory, behave as if var `foo` was `setq-default` to `bar`".

> However, I've also just noticed that Emacs 26.1 appears to have broken/
> inverted the way that such overrides work.
>
> https://emacs.stackexchange.com/a/46005/454

That looks like a bug.


        Stefan

Re: dir-local vs major-mode setting

[Phil Sainty]

On 15/11/18 4:27 PM, Stefan Monnier wrote:
>> However, I've also just noticed that Emacs 26.1 appears to have broken/
>> inverted the way that such overrides work.
>>
>> https://emacs.stackexchange.com/a/46005/454
> 
> That looks like a bug.

n.b. That has now been raised as bug#33400

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=33400