Clarification on hooks and custom-set-variables

Clarification on hooks and custom-set-variables

[Tassilo Horn]

Hi all,

this is related to AUCTeX bug#21188.  The problem is this: A user who
uses AUCTeX from ELPA customized `LaTeX-mode-hook' so that

  (custom-set-variables
   '(LaTeX-mode-hook '(flyspell-mode LaTeX-math-mode turn-on-reftex)))

is in his ~/.emacs.  I can reproduce the problem with this being the
only contents of ~/.emacs.

Now when he starts emacs, the value of `LaTeX-mode-hook' will be
'(LaTeX-preview-setup).  Huh, where are the configs gone?

AUCTeX uses `LaTeX-mode-hook' internally, too.  auctex-autoloads.el adds
the preview setup function

  (add-hook 'LaTeX-mode-hook #'LaTeX-preview-setup)

which in turn does

  (remove-hook 'LaTeX-mode-hook #'LaTeX-preview-setup)
  (add-hook 'LaTeX-mode-hook #'preview-mode-setup)

But `add-hook' / `remove-hook' should be harmless, and there's no place
where `LaTeX-mode-hook' would be set.

If we add a t NOW flag to the customization, it works.  After startup,
`LaTeX-mode-hook' is the customized value plus `LaTeX-preview-setup'.

The `custom-set-variables' docs don't tell me when customizations are
applied when NOW is omitted or nil.  I guess, it'll be done just when
the corresponding defcustom form is evaluated, right?

So a shot in the blue would be:

  1. Emacs starts and stores the customization value for later
     application since `LaTeX-mode-hook' isn't defined yet.
  2. `package-initialize' runs which loads auctex-autoloads.el which
     adds `LaTeX-preview-setup' to `LaTeX-mode-hook'.
  3. Eventually, latex.el gets loaded and evals the (defcustom
     LaTeX-mode-hook nil) form.  Now customization should kick in but
     maybe it skips applying the customized value because the current
     value '(LaTeX-preview-setup) differs from the default value?

Does that make sense?  Or why does the customized value get lost?  And
most importantly, how to I fix that?

Bye,
Tassilo

Re: Clarification on hooks and custom-set-variables

[Stefan Monnier]

>   (custom-set-variables
>    '(LaTeX-mode-hook '(flyspell-mode LaTeX-math-mode turn-on-reftex)))
[...]
> Now when he starts emacs, the value of `LaTeX-mode-hook' will be
> '(LaTeX-preview-setup).  Huh, where are the configs gone?

Not applied (yet).  What happens after he opens a LaTeX file?

> AUCTeX uses `LaTeX-mode-hook' internally, too.  auctex-autoloads.el adds
> the preview setup function
>   (add-hook 'LaTeX-mode-hook #'LaTeX-preview-setup)

FWIW, this probably made sense back when latex-preview was a separate
package, but now you're better off calling LaTeX-preview-setup
unconditionally from AUCTeX's latex-mode.

> The `custom-set-variables' docs don't tell me when customizations are
> applied when NOW is omitted or nil.  I guess, it'll be done just when
> the corresponding defcustom form is evaluated, right?

Sound be, yes.

> Does that make sense?  Or why does the customized value get lost?  And
> most importantly, how to I fix that?

Custom just sucks at handling vars which are both set via Custom and set
by random Elisp code.  E.g. depending on the circumstances, you could
end up with only (flyspell-mode LaTeX-math-mode turn-on-reftex) in the
hook, i.e. without LaTeX-preview-setup.

The best fixes I can think of:
- don't make it a defcustom.
- split it into a defcustom (only set by the user) and a defvar (only
  set by Elisp code).


        Stefan

Re: Clarification on hooks and custom-set-variables

[Tassilo Horn]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Now when he starts emacs, the value of `LaTeX-mode-hook' will be
>> '(LaTeX-preview-setup).  Huh, where are the configs gone?
>
> Not applied (yet).  What happens after he opens a LaTeX file?

Then it contains just `preview-mode-setup'.  That's because
`LaTeX-preview-setup' replaces itself with that.  In any case, the user
configs won't be applied.

>> AUCTeX uses `LaTeX-mode-hook' internally, too.  auctex-autoloads.el adds
>> the preview setup function
>>   (add-hook 'LaTeX-mode-hook #'LaTeX-preview-setup)
>
> FWIW, this probably made sense back when latex-preview was a separate
> package, but now you're better off calling LaTeX-preview-setup
> unconditionally from AUCTeX's latex-mode.

Indeed.

>> The `custom-set-variables' docs don't tell me when customizations are
>> applied when NOW is omitted or nil.  I guess, it'll be done just when
>> the corresponding defcustom form is evaluated, right?
>
> Sound be, yes.
>
>> Does that make sense?  Or why does the customized value get lost?
>> And most importantly, how to I fix that?
>
> Custom just sucks at handling vars which are both set via Custom and
> set by random Elisp code.  E.g. depending on the circumstances, you
> could end up with only (flyspell-mode LaTeX-math-mode turn-on-reftex)
> in the hook, i.e. without LaTeX-preview-setup.
>
> The best fixes I can think of:
> - don't make it a defcustom.

Probably that ship has sailed since it has been a defcustom for ages.

> - split it into a defcustom (only set by the user) and a defvar (only
>   set by Elisp code).

Well, in this concrete case I just go with calling `LaTeX-preview-setup'
unconditionally.

Bye,
Tassilo