bug#69501: 30.0.50; customize-mode error with substring completion style

bug#69501: 30.0.50; customize-mode error with substring completion style

[Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Hi,

With both Emacs 29.2 and with the current master:

1. emacs -Q
2. (setq completion-styles '(substring))
3. C-u M-x customize-mode TAB
4. "Assertion failed: (stringp suffix)"

I not sure exactly why this error occurs, but IIUC it has to do with the
fact that customize-mode let-binds completion-regexp-list.  I suspect
that the substring completion style doesn't handle that correctly.

In general, let-binding completion-regexp-list around completing-read is
not a great idea IMO because it affects recursive minibuffers as well.
So perhaps the best solution is to avoid doing that in customize-mode,
and to rely only on the predicate argument of completing-read instead?


Best,

Eshel

bug#69501: 30.0.50; customize-mode error with substring completion style

[Eli Zaretskii]

> Date: Sat, 02 Mar 2024 09:59:48 +0100
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> With both Emacs 29.2 and with the current master:
> 
> 1. emacs -Q
> 2. (setq completion-styles '(substring))
> 3. C-u M-x customize-mode TAB
> 4. "Assertion failed: (stringp suffix)"
> 
> I not sure exactly why this error occurs, but IIUC it has to do with the
> fact that customize-mode let-binds completion-regexp-list.  I suspect
> that the substring completion style doesn't handle that correctly.
> 
> In general, let-binding completion-regexp-list around completing-read is
> not a great idea IMO because it affects recursive minibuffers as well.
> So perhaps the best solution is to avoid doing that in customize-mode,
> and to rely only on the predicate argument of completing-read instead?

Stefan and Mauro, any suggestions?

bug#69501: 30.0.50; customize-mode error with substring completion style

[Mauro Aranda]

On 4/3/24 10:16, Eli Zaretskii wrote:
 >> Date: Sat, 02 Mar 2024 09:59:48 +0100
 >> From:  Eshel Yaron via "Bug reports for GNU Emacs,
 >>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
 >>
 >> With both Emacs 29.2 and with the current master:
 >>
 >> 1. emacs -Q
 >> 2. (setq completion-styles '(substring))
 >> 3. C-u M-x customize-mode TAB
 >> 4. "Assertion failed: (stringp suffix)"
 >>
 >> I not sure exactly why this error occurs, but IIUC it has to do with the
 >> fact that customize-mode let-binds completion-regexp-list.  I suspect
 >> that the substring completion style doesn't handle that correctly.
 >>
 >> In general, let-binding completion-regexp-list around completing-read is
 >> not a great idea IMO because it affects recursive minibuffers as well.
 >> So perhaps the best solution is to avoid doing that in customize-mode,
 >> and to rely only on the predicate argument of completing-read instead?
 >
 > Stefan and Mauro, any suggestions?

I took a quick look, but I don't know how "relying on the predicate
argument of completing-read" looks in practice.  It seems I have
forgotten how to use the completion functions (if I ever knew how to use
them at all).  Hopefully Stefan will be of more help.

bug#69501: 30.0.50; customize-mode error with substring completion style

[Eli Zaretskii]

> Date: Tue, 5 Mar 2024 09:36:01 -0300
> Cc: 69501@debbugs.gnu.org
> From: Mauro Aranda <maurooaranda@gmail.com>
> 
> On 4/3/24 10:16, Eli Zaretskii wrote:
>  >> Date: Sat, 02 Mar 2024 09:59:48 +0100
>  >> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  >>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>  >>
>  >> With both Emacs 29.2 and with the current master:
>  >>
>  >> 1. emacs -Q
>  >> 2. (setq completion-styles '(substring))
>  >> 3. C-u M-x customize-mode TAB
>  >> 4. "Assertion failed: (stringp suffix)"
>  >>
>  >> I not sure exactly why this error occurs, but IIUC it has to do with the
>  >> fact that customize-mode let-binds completion-regexp-list.  I suspect
>  >> that the substring completion style doesn't handle that correctly.
>  >>
>  >> In general, let-binding completion-regexp-list around completing-read is
>  >> not a great idea IMO because it affects recursive minibuffers as well.
>  >> So perhaps the best solution is to avoid doing that in customize-mode,
>  >> and to rely only on the predicate argument of completing-read instead?
>  >
>  > Stefan and Mauro, any suggestions?
> 
> I took a quick look, but I don't know how "relying on the predicate
> argument of completing-read" looks in practice.  It seems I have
> forgotten how to use the completion functions (if I ever knew how to use
> them at all).  Hopefully Stefan will be of more help.

Stefan?

bug#69501: 30.0.50; customize-mode error with substring completion style

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> In general, let-binding completion-regexp-list around completing-read is
> not a great idea IMO

Definitely: `completion-regexp-list` should be let-bound only right
around calls to `try/all-completions`.

> because it affects recursive minibuffers as well.
> So perhaps the best solution is to avoid doing that in customize-mode,
> and to rely only on the predicate argument of completing-read instead?

Indeed (see patch below).

We should probably also change the completion code so it defends against
such let-bindings of `completion-regexp-list`.


        Stefan


diff --git a/lisp/cus-edit.el b/lisp/cus-edit.el
index 8fad51dc116..f004002333b 100644
--- a/lisp/cus-edit.el
+++ b/lisp/cus-edit.el
@@ -1159,14 +1159,15 @@ customize-mode
 for the MODE to customize."
   (interactive
    (list
-    (let ((completion-regexp-list '("-mode\\'"))
-	  (group (custom-group-of-mode major-mode)))
+    (let ((group (custom-group-of-mode major-mode)))
       (if (and group (not current-prefix-arg))
 	  major-mode
 	(intern
 	 (completing-read (format-prompt "Mode" (and group major-mode))
 			  obarray
-			  'custom-group-of-mode
+			  (lambda (s)
+			    (and (string-match "-mode\\'" (symbol-name s))
+			         (custom-group-of-mode s)))
 			  t nil nil (if group (symbol-name major-mode))))))))
   (customize-group (custom-group-of-mode mode)))
 

bug#69501: 30.0.50; customize-mode error with substring completion style

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> Indeed (see patch below).

Pushed to `master`.


        Stefan