Temporarily suppress a hook?

Temporarily suppress a hook?

[Skip Montanaro]

I have before-save-hook defined in ~/.emacs

(add-hook 'before-save-hook 'delete-trailing-whitespace)

This is useful almost all the time. I just discovered a case where
it's not so helpful (a file full of regular expressions to feed into
"grep -E -f ..."

I can think of various ways to tweak the regular expressions to not
require trailing whitespace, but let's assume for a moment that's not
possible. Is it possible to suppress the before-save-hook on a
per-file basis?

Thx,

Skip

RE: Temporarily suppress a hook?

[Drew Adams]

> I have before-save-hook defined in ~/.emacs
> (add-hook 'before-save-hook 'delete-trailing-whitespace)
> 
> This is useful almost all the time. I just discovered a case where
> it's not so helpful (a file full of regular expressions to feed into
> "grep -E -f ..."
> 
> I can think of various ways to tweak the regular expressions to not
> require trailing whitespace, but let's assume for a moment that's not
> possible. Is it possible to suppress the before-save-hook on a
> per-file basis?

Both `add-hook' and `remove-hook' take an optional
LOCAL argument, to affect only the current buffer
(the buffer-local value of the hook).

Re: Temporarily suppress a hook?

[Skip Montanaro]

> I have before-save-hook defined in ~/.emacs
> > (add-hook 'before-save-hook 'delete-trailing-whitespace)


Both `add-hook' and `remove-hook' take an optional
> LOCAL argument, to affect only the current buffer
> (the buffer-local value of the hook).
>

It's not clear how that helps me. In essentially every other file I edit, I
want to delete trailing whitespace, so I enable it globally. It seems
buffer-local enabling of that hook would be appropriate if I only
occasionally wanted to enable it.

Skip

>

Re: Temporarily suppress a hook?

[Bob Proulx]

Skip Montanaro wrote:
> Is it possible to suppress the before-save-hook on a
> per-file basis?

I know this isn't quite what you are wanting but sometimes a crazy
squirrel cage argument which is outside the normal box can still be
useful...

Could you suppress you entire .emacs so as to avoid all of your
customization?

  emacs -q that-special-flie

Or you would pick another user on your system that has a compatible
file to you but without the hooks.  Perhaps root?  Perhaps another
user?  Use their .emacs file for that one file.

  emacs -u root that-special-flie

I know that will be less desirable for many reasons.  You won't get
your normal configuration for other things.  But if you can take a
default configuration for just that moment then it would suppress your
hooks as they would not be added then.

Bob

Re: Temporarily suppress a hook?

[Óscar Fuentes]

Skip Montanaro <skip.montanaro@gmail.com> writes:

> I have before-save-hook defined in ~/.emacs
>
> (add-hook 'before-save-hook 'delete-trailing-whitespace)
>
> This is useful almost all the time. I just discovered a case where
> it's not so helpful (a file full of regular expressions to feed into
> "grep -E -f ..."
>
> I can think of various ways to tweak the regular expressions to not
> require trailing whitespace, but let's assume for a moment that's not
> possible. Is it possible to suppress the before-save-hook on a
> per-file basis?

AFAIK, no. But you can use your own function instead of
delete-trailing-whitespace:

(defun my-delete-trailing-whitespace ()
  (interactive)
  (unless my-special-buffer
    (delete-trailing-whitespace)))

(add-hook 'before-save-hook 'my-delete-trailing-whitespace)

Or advice delete-trailing-whitespace.

Re: Temporarily suppress a hook?

[tomas]

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On Mon, Jul 09, 2018 at 07:21:12AM +0200, Óscar Fuentes wrote:
> Skip Montanaro <skip.montanaro@gmail.com> writes:

[...]

> AFAIK, no. But you can use your own function instead of
> delete-trailing-whitespace:
> 
> (defun my-delete-trailing-whitespace ()
>   (interactive)
>   (unless my-special-buffer
>     (delete-trailing-whitespace)))

> (add-hook 'before-save-hook 'my-delete-trailing-whitespace)
> 
> Or advice delete-trailing-whitespace.

Or perhaps make the hook read a local variable you set in
the file (see "file local variables") and act accordingly.

This way you could declare whithin those special files that you
don't want trailing space removed.

Cheers
- -- t
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Re: Temporarily suppress a hook?

[Óscar Fuentes]

<tomas@tuxteam.de> writes:

> On Mon, Jul 09, 2018 at 07:21:12AM +0200, Óscar Fuentes wrote:
>> Skip Montanaro <skip.montanaro@gmail.com> writes:
>
> [...]
>
>> AFAIK, no. But you can use your own function instead of
>> delete-trailing-whitespace:
>> 
>> (defun my-delete-trailing-whitespace ()
>>   (interactive)
>>   (unless my-special-buffer
>>     (delete-trailing-whitespace)))
>
>> (add-hook 'before-save-hook 'my-delete-trailing-whitespace)
>> 
>> Or advice delete-trailing-whitespace.
>
> Or perhaps make the hook read a local variable you set in
> the file (see "file local variables") and act accordingly.
>
> This way you could declare whithin those special files that you
> don't want trailing space removed.

I thought that it was unnecessary to explain that my-special-buffer is
whatever predicate the OP feels convenient.

Re: Temporarily suppress a hook?

[Skip Montanaro]

On Mon, Jul 9, 2018, 1:00 AM <tomas@tuxteam.de> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Mon, Jul 09, 2018 at 07:21:12AM +0200, Óscar Fuentes wrote:
> > Skip Montanaro <skip.montanaro@gmail.com> writes:
>
> [...]
>
> > AFAIK, no. But you can use your own function instead of
> > delete-trailing-whitespace:
> >
> > (defun my-delete-trailing-whitespace ()
> >   (interactive)
> >   (unless my-special-buffer
> >     (delete-trailing-whitespace)))
>
> > (add-hook 'before-save-hook 'my-delete-trailing-whitespace)
> >
> > Or advice delete-trailing-whitespace.
>
> Or perhaps make the hook read a local variable you set in
> the file (see "file local variables") and act accordingly.
>
> This way you could declare whithin those special files that you
> don't want trailing space removed.
>

Thanks all. Óscar's idea seems to come closest to a solution. I might use
that to suppress the hook for files with, say, a ".txt" extension. Those
would benefit least from scrubbing all trailing whitespace. Or... I could
use a prefix argument and check to see if it's been set to a magic value.
C-u -7 C-x C-s. Assuming I can read any prefix arg set by the user.

Unfortunately, file local variables aren't too helpful here. "grep -f file"
reads a series of patterns from the named file, so interprets every line as
a pattern. While it might work to track on a file local variable section,
you run the risk of a line being a false positive match for a line in the
file(s) you're running grep against.

Skip

>

Re: Temporarily suppress a hook?

[João Távora]

On Mon, Jul 9, 2018, 02:40 Skip Montanaro <skip.montanaro@gmail.com> wrote:

> > I have before-save-hook defined in ~/.emacs
> > > (add-hook 'before-save-hook 'delete-trailing-whitespace)
>
>
> Both `add-hook' and `remove-hook' take an optional
> > LOCAL argument, to affect only the current buffer
> > (the buffer-local value of the hook).
> >
>
> It's not clear how that helps me. In essentially every other file I edit, I
> want to delete trailing whitespace, so I enable it globally. It seems
> buffer-local enabling of that hook would be appropriate if I only
> occasionally wanted to enable it.
>

Indeed, using remove-hook with a local argument in those special buffers
won't help you if you've already affected the global value of
before-save-hook.

But you can add the hook locally, as Drew suggests, in those buffers where
you need it, and refrain from doing so in the buffers where you don't.
Prog-mode is a very pervasive mode: many modes derive from it.

Here's what I mean

(add-hook 'prog-mode-hook
  (lambda ()
    (add-hook 'before-save-hook 'delete-trailing-whitespace nil t)))

Now, in those special files/buffers (some special major mode?), a
remove-hook should do what you want.

João

Re: Temporarily suppress a hook?

[Stefan Monnier]

> I have before-save-hook defined in ~/.emacs
> (add-hook 'before-save-hook 'delete-trailing-whitespace)
[...]
> possible.  Is it possible to suppress the before-save-hook on a
> per-file basis?

I suggest you file a feature request (via M-x report-emacs-bug)

I think it should be possible to buffer-locally "remove" a function from
a hook, even if that function was added globally (I toyed with an
implementation of that idea which added `(not . FUNCTION)` to the
(buffer-local part of the) hook, and then `run-hook` would honor such
a value by disregarding any subsequent occurrence of FUNCTION).

With my hack, you'd be able to do:

    (add-hook 'my-special-mode-hook
              (lambda ()
                (remove-hook 'before-save-hook
                             #'delete-trailing-whitespace 'local)))

so that buffers using `my-special-mode` won't delete their trailing spaces.


        Stefan

Re: Temporarily suppress a hook?

[Marcin Borkowski]

On 2018-07-09, at 13:01, Skip Montanaro <skip.montanaro@gmail.com> wrote:

> C-u -7 C-x C-s. Assuming I can read any prefix arg set by the user.

Yes, you can.  See http://mbork.pl/2017-07-09_current-prefix-arg and an
example use in http://mbork.pl/2018-07-02_Smart_yanking .

Hth,

-- 
Marcin Borkowski
http://mbork.pl

Re: Temporarily suppress a hook?

[Emanuel Berg]

Skip Montanaro wrote:

> I have before-save-hook defined in ~/.emacs
>
> (add-hook 'before-save-hook
> 'delete-trailing-whitespace)
>
> This is useful almost all the time. I just
> discovered a case where it's not so helpful
> (a file full of regular expressions to feed
> into "grep -E -f ..."
>
> I can think of various ways to tweak the
> regular expressions to not require trailing
> whitespace, but let's assume for a moment
> that's not possible. Is it possible to
> suppress the before-save-hook on
> a per-file basis?

You just need to find some property of the
exception file by which it is identifiable to
the program (that is executing the hook
functionality), be it its mode (best, as easily
checked), file name suffix, or some property of
the text (which might be more difficult to get
unambiguously right). Then just do like this:

;; (setq before-save-hook nil)
(defun before-save-hook-f ()
  ;; insert `if' branch here, and
  ;; don't do anything if such a file, else
  ;; do:
  (delete-trailing-whitespace) )
(add-hook 'before-save-hook #'before-save-hook-f)

BTW for everyone viewing pleasure here is
a "one shot hook" that is executed only once,
i.e. it removes itself after the first
execution:

(defun add-one-shot-hook-args-ignored (hook fun)
  (let ((name (cl-gensym)))
    (setf (symbol-function name)
          (lambda (&rest _unused)
            (remove-hook hook name)
            (funcall fun) ))
    (add-hook hook name) ))

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