GNU bug report logs - #12254
24.2; completion fails backward-char

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Leo <sdl.web <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2; completion fails backward-char
Date: Wed, 22 Aug 2012 10:40:25 +0800

[Message part 1 (text/plain, inline)]

This is a regression. It doesn't happen in Emacs 23.4.

1. Emacs -q -l b.el (b.el is attached)
2. M-x b-mode
3. Type I followed by <tab> to complete to IGNORE
4. C-b

In step 4, C-b could not move backwards; point appears to be trapped
there.

Leo

[b.el (application/emacs-lisp, inline)]

Message #8 received at 12254 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Leo <sdl.web <at> gmail.com>
Cc: 12254 <at> debbugs.gnu.org
Subject: Re: bug#12254: 24.2; completion fails backward-char
Date: Wed, 22 Aug 2012 12:17:27 -0400

Thanks for those bug reports, Leo.
I'm probably to blame for most/all of those completion problems, but I'm
just coming back from a vacation and have to prepare for the "beginning
of the end of the semester" (for reasons of student strikes (tho
I guess it's probably more due to government's obtuseness), we're about
to resume classes for the last 4 weeks of the winter semester ;-).
So, I'll try to look at it ASAP, but you may have to wait a week or two.


        Stefan

Message #15 received at 12254-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Leo <sdl.web <at> gmail.com>
Cc: 12254-done <at> debbugs.gnu.org
Subject: Re: bug#12254: 24.2; completion fails backward-char
Date: Wed, 29 Aug 2012 14:05:19 -0400

tags 12254 notabug
thanks

> (defun b-completion-at-point ()
>   (let ((beg (progn
>                (skip-syntax-backward "w")
>                (point)))
>         (end (progn
>                (skip-syntax-forward "w")
>                (point))))
>     (list beg end '("IGNORE" "DEBUG" "HELLO"))))

This needs to save-excursion.

> This is a regression. It doesn't happen in Emacs 23.4.

That's only because completion-at-point-functions is used less often so
the bug in the above code doesn't bite as often.
But your above completion function is already buggy in Emacs-23.4 since
it can't complete "IG!R" to "IGNORE", whereas after adding the
save-excursion such completion works just fine.


        Stefan

Message #18 received at 12254 <at> debbugs.gnu.org (full text, mbox):

From: Leo <sdl.web <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 12254 <at> debbugs.gnu.org
Subject: Re: bug#12254: 24.2; completion fails backward-char
Date: Thu, 30 Aug 2012 20:05:03 +0800

On 2012-08-30 02:05 +0800, Stefan Monnier wrote:
> That's only because completion-at-point-functions is used less often so
> the bug in the above code doesn't bite as often.
> But your above completion function is already buggy in Emacs-23.4 since
> it can't complete "IG!R" to "IGNORE", whereas after adding the
> save-excursion such completion works just fine.

Thank you for this.

This isn't clear on the documentation on completion-at-point-functions.
It is a trap that one can easily fall into. I wonder if you may add a
note in the doc-string of completion-at-point-functions. Thanks.

Leo

Message #21 received at 12254 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Leo <sdl.web <at> gmail.com>
Cc: 12254 <at> debbugs.gnu.org
Subject: Re: bug#12254: 24.2; completion fails backward-char
Date: Thu, 30 Aug 2012 11:39:59 -0400

> This isn't clear on the documentation on completion-at-point-functions.
> It is a trap that one can easily fall into. I wonder if you may add a
> note in the doc-string of completion-at-point-functions. Thanks.

How 'bout the patch below?


        Stefan


=== modified file 'lisp/minibuffer.el'
--- lisp/minibuffer.el	2012-08-14 17:10:38 +0000
+++ lisp/minibuffer.el	2012-08-30 15:39:14 +0000
@@ -1821,7 +1821,9 @@
  `:predicate'	a predicate that completion candidates need to satisfy.
  `:exclusive'	If `no', means that if the completion table fails to
    match the text at point, then instead of reporting a completion
-   failure, the completion should try the next completion function.")
+   failure, the completion should try the next completion function.
+As is the case with most hooks, the functions are responsible to preserve
+things like point and current buffer.")
 
 (defvar completion--capf-misbehave-funs nil
   "List of functions found on `completion-at-point-functions' that misbehave.

Message #24 received at 12254 <at> debbugs.gnu.org (full text, mbox):

From: Leo <sdl.web <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 12254 <at> debbugs.gnu.org
Subject: Re: bug#12254: 24.2; completion fails backward-char
Date: Fri, 31 Aug 2012 06:25:31 +0800

On 2012-08-30 23:39 +0800, Stefan Monnier wrote:
> === modified file 'lisp/minibuffer.el'
> --- lisp/minibuffer.el	2012-08-14 17:10:38 +0000
> +++ lisp/minibuffer.el	2012-08-30 15:39:14 +0000
> @@ -1821,7 +1821,9 @@
>   `:predicate'	a predicate that completion candidates need to satisfy.
>   `:exclusive'	If `no', means that if the completion table fails to
>     match the text at point, then instead of reporting a completion
> -   failure, the completion should try the next completion function.")
> +   failure, the completion should try the next completion function.
> +As is the case with most hooks, the functions are responsible to preserve
> +things like point and current buffer.")
>  
>  (defvar completion--capf-misbehave-funs nil
>    "List of functions found on `completion-at-point-functions' that misbehave.

Thank you. That looks good ;)

Leo

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