GNU bug report logs - #5293
23.1; unload-feature on buffer-local hooks

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Juanma Barranquero <lekktu <at> gmail.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#5293: closed (23.1; unload-feature on buffer-local hooks)
Date: Wed, 13 Jul 2011 20:29:02 +0000

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Your message dated Wed, 13 Jul 2011 22:28:02 +0200
with message-id <CAAeL0SS_nH7ywDknYydqfd+7qMmhEDjN0rG4KjtOs=hfyxWAyQ <at> mail.gmail.com>
and subject line Re: bug#5293: 23.1; unload-feature on buffer-local hooks
has caused the GNU bug report #5293,
regarding 23.1; unload-feature on buffer-local hooks
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
5293: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=5293
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From: Kevin Ryde <user42 <at> zip.com.au>
To: bug-gnu-emacs <at> gnu.org
Subject: 23.1; unload-feature on buffer-local hooks
Date: Sun, 03 Jan 2010 08:06:14 +1100

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When `unload-feature' looks in hooks for functions that it's going to
unload, it doesn't seem to look in buffer-local values, other than for
the current buffer.

Evalling the code in try-foo.el below loads then unloads foo.el.  It
gets an error

    void-function foo-message

where I hoped unload-feature might have purged that `foo-message' from
`after-change-functions'.

I suppose looking in all buffers is more work for unload-feature, but
would be a good protection against bad things happening later.  I expect
some of the standard hooks like `after-change-functions' are used
buffer-local most of the time.

If instead it's an intentional omission (to save work) then the elisp
manual and the docstring could note it so that modes or packages using
buffer-local hook settings can take steps to undo.

[foo.el (application/emacs-lisp, attachment)]

[try-foo.el (application/emacs-lisp, attachment)]

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In GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.16.5)
 of 2009-09-14 on raven, modified by Debian
configured using `configure  '--build=i486-linux-gnu' '--host=i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_AU
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-1-unix
  default-enable-multibyte-characters: t

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From: Juanma Barranquero <lekktu <at> gmail.com>
To: Kevin Ryde <user42 <at> zip.com.au>
Cc: 5293-done <at> debbugs.gnu.org
Subject: Re: bug#5293: 23.1; unload-feature on buffer-local hooks
Date: Wed, 13 Jul 2011 22:28:02 +0200

> Evalling the code in try-foo.el below loads then unloads foo.el.  It
> gets an error
>
>    void-function foo-message
>
> where I hoped unload-feature might have purged that `foo-message' from
> `after-change-functions'.
>
> I suppose looking in all buffers is more work for unload-feature, but
> would be a good protection against bad things happening later.  I expect
> some of the standard hooks like `after-change-functions' are used
> buffer-local most of the time.

You're right that some hooks are used buffer-locally most of the time,
but it's also true that in many cases they are used from a major mode,
i.e., in your case, if foo.el defined a foo-mode and set
`after-change-functions' locally in foo-mode buffers, unload-feature
would do OK (with the current trunk, not any released Emacsen).

As it is, foo.el is doing something non-standard, and unload-feature
cannot try to revert by itself every non-standard thing packages do.
That's why FEATURE-unload-function exists. So, in this case, the right
fix would be adding this function to foo.el:

(defun foo-unload-function ()
  "Unload foo.el."
  (ignore-errors
    (with-current-buffer (get-buffer "foo-buffer")
      (remove-hook 'after-change-functions 'foo-message t)))
  ;; continue standard unloading
  nil)

That said, there are improvements that could be made to unload-feature
(for example, trying to automatically deactivate minor modes being
undefined), but I'm not sure that looking in every buffer-local
variable of every live buffer is a sensible thing to do. I'm closing
this one because it is not really a bug. We can open a wishlist bug
for unload-feature is you want.

    Juanma

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