GNU bug report logs - #76817
30.1; completion-preview and shell

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

From: Rufus Segar <rhs <at> riseup.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.1; completion-preview and shell
Date: Fri, 07 Mar 2025 16:38:11 +0000

It appears that completion-preview-mode is not quite working as intended
with shell. When inserting path completions it inserts a trailing space.

An example will show why this is undesirable:

Say I want to complete path `~/foobar/baz'. I start with `cd ~/foob` and
completion-preview successfully completes the 'foobar' portion. However,
after I do completion-preview-insert I'm left with the following:

"cd ~/foobar/ "
             ^-- Notice the trailing space

This means that if I want to continue completing my path all the way to
'~/foobar/baz', I have to delete that trailing space. completion-preview
should not leave a trailing space, and if possible immediately continue
completing the path, so that in this case I'm given '~/foobar/baz' as my
next completion candidate and can simply call completion-preview-insert
again to get the full path.

P.S. I'm loving completion-preview-mode by the way, I can tell that a
lot of care was put into this mode. I'm looking forward to this issue
being resolved so that I can use it in my shell too.

=====

I have tested this with `emacs -q` and have observed the same behavior.
However, here is the auto-filled info from report-emacs-bug:

In GNU Emacs 30.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.48,
cairo version 1.18.2)
Windowing system distributor 'The X.Org Foundation', version 11.0.12101015
System Description: Arch Linux

Configured using:
 'configure --sysconfdir=/etc --prefix=/usr --libexecdir=/usr/lib
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Configured features:
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Important settings:
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Major mode: mu4e:main

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Load-path shadows:
/home/vent/.emacs.d/straight/build/transient/transient hides /usr/share/emacs/30.1/lisp/transient
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-- 
Thanks,
~Rufus

Message #8 received at 76817 <at> debbugs.gnu.org (full text, mbox):

From: Eshel Yaron <me <at> eshelyaron.com>
To: Rufus Segar <rhs <at> riseup.net>
Cc: 76817 <at> debbugs.gnu.org
Subject: Re: bug#76817: 30.1; completion-preview and shell
Date: Fri, 07 Mar 2025 19:47:09 +0100

Hi Rufus,

Rufus Segar <rhs <at> riseup.net> writes:

> It appears that completion-preview-mode is not quite working as intended
> with shell. When inserting path completions it inserts a trailing space.

The trailing space comes from the :exit-function that the completion
backend specifies.  completion-preview-mode calls that :exit-function
when you insert a completion suggestion, so in that sense it does work
as intended.

Of course, I agree that this trailing space is undesirable for exactly
the reason you describe below.  You can disable it, as I do, by setting
either pcomplete-termination-string or pcomplete-exit-function.  Do you
get a better behavior with (setq pcomplete-termination-string "") ?

> An example will show why this is undesirable:
>
> Say I want to complete path `~/foobar/baz'. I start with `cd ~/foob` and
> completion-preview successfully completes the 'foobar' portion. However,
> after I do completion-preview-insert I'm left with the following:
>
> "cd ~/foobar/ "
>              ^-- Notice the trailing space
>
> This means that if I want to continue completing my path all the way to
> '~/foobar/baz', I have to delete that trailing space. completion-preview
> should not leave a trailing space, and if possible immediately continue
> completing the path, so that in this case I'm given '~/foobar/baz' as my
> next completion candidate and can simply call completion-preview-insert
> again to get the full path.
>
> P.S. I'm loving completion-preview-mode by the way, I can tell that a
> lot of care was put into this mode. I'm looking forward to this issue
> being resolved so that I can use it in my shell too.

Thanks!

Eshel

Message #11 received at 76817 <at> debbugs.gnu.org (full text, mbox):

From: Eshel Yaron <me <at> eshelyaron.com>
To: Rufus Segar <rhs <at> riseup.net>
Cc: 76817 <at> debbugs.gnu.org
Subject: Re: bug#76817: 30.1; completion-preview and shell
Date: Fri, 14 Mar 2025 17:59:58 +0100

[ Resending with the mailing list back in CC. ]

Hi Rufus,

Rufus Segar <rhs <at> riseup.net> writes:

> Hey Eshel,
>
>> Of course, I agree that this trailing space is undesirable for exactly
>> the reason you describe below.  You can disable it, as I do, by setting
>> either pcomplete-termination-string or pcomplete-exit-function.  Do you
>> get a better behavior with (setq pcomplete-termination-string "") ?
>
> Thanks! I added a hook to comint-mode to (setq pcomplete-termination-string "")
> and this has resolved the issue for me. Its working great now, so thanks again.

Great, thanks for confirming.

There's an alternative to setting pcomplete-termination-string directly,
which is to set comint-completion-addsuffix e.g. to nil.  Shell mode
consults this variable to and sets pcomplete-termination-string
accordingly, so if you set comint-completion-addsuffix once you don't
need to set pcomplete-termination-string via a hook.

I'd really like to make this work as you expect by default, so users
won't need this piece of configuration.  It's not hard to configure but
it's kind of an annoying gotcha...  It's mostly a matter of picking the
right place to tweak, since there are several intertwined components
that come into play.  For example, pcomplete-default-exit-function can
check if the completion ends with a directory separator (/), and if so
avoid adding pcomplete-termination-string.  I'll give it some thought,
and maybe someone who already gave it some thought will chime in too :)

>> The trailing space comes from the :exit-function that the completion
>> backend specifies.  completion-preview-mode calls that :exit-function
>> when you insert a completion suggestion, so in that sense it does work
>> as intended.
>
> I see. Interesting how it still inserts a trailing space after
> completing shell commands, even with the path completion fix described
> above. The trailing space is desirable here, so I ain't complaining,
> just curious.

Yeah, completion in Shell buffers is... involved.  In this case a
different :exit-function is in effect, which inserts a space regardless
of pcomplete-termination-string.  See shell--command-completion-data.


Regards,

Eshel

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