bug#68602: 29.2; describe-language-environment fails to specify default in its CR

bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Thierry Volpiatto]

Its read-language-name specify default in prompt but not as DEFAULT arg.

diff --git a/lisp/international/mule-cmds.el b/lisp/international/mule-cmds.el
index 07f11a62594..666912300a7 100644
--- a/lisp/international/mule-cmds.el
+++ b/lisp/international/mule-cmds.el
@@ -2159,7 +2159,8 @@ See `set-language-info-alist' for use in programs."
   (interactive
    (list (read-language-name
 	  'documentation
-	  (format-prompt "Describe language environment" current-language-environment))))
+	  (format-prompt "Describe language environment" current-language-environment)
+          current-language-environment)))
   (let ((help-buffer-under-preparation t))
     (if (null language-name)
 	(setq language-name current-language-environment))



In GNU Emacs 29.2 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
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System Description: Linux Mint 21.3

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-- 
Thierry

bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Eli Zaretskii]

> From: Thierry Volpiatto <thievol@posteo.net>
> Date: Sat, 20 Jan 2024 05:56:11 +0000
> 
> 
> Its read-language-name specify default in prompt but not as DEFAULT arg.

Thanks.  But why is that a problem?

bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Thierry Volpiatto]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Thierry Volpiatto <thievol@posteo.net>
>> Date: Sat, 20 Jan 2024 05:56:11 +0000
>> 
>> 
>> Its read-language-name specify default in prompt but not as DEFAULT arg.
>
> Thanks.  But why is that a problem?

Because Helm needs this info to handle DEFAULT, it can't be aware of the
code running after the completing-read (read-language-name in this
case).
Also using the DEFAULT arg of read-language-name save you the
need to compute DEFAULT just after:

    (if (null language-name)
        (setq language-name current-language-environment))

This piece of code can be removed.

-- 
Thierry

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bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Eli Zaretskii]

> From: Thierry Volpiatto <thievol@posteo.net>
> Cc: 68602@debbugs.gnu.org
> Date: Sat, 20 Jan 2024 16:37:04 +0000
> 
> >> From: Thierry Volpiatto <thievol@posteo.net>
> >> Date: Sat, 20 Jan 2024 05:56:11 +0000
> >> 
> >> 
> >> Its read-language-name specify default in prompt but not as DEFAULT arg.
> >
> > Thanks.  But why is that a problem?
> 
> Because Helm needs this info to handle DEFAULT, it can't be aware of the
> code running after the completing-read (read-language-name in this
> case).

Can you elaborate on this?  I don't think I follow (I don't use Helm).

> Also using the DEFAULT arg of read-language-name save you the
> need to compute DEFAULT just after:
> 
>     (if (null language-name)
>         (setq language-name current-language-environment))
> 
> This piece of code can be removed.

Right.

bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Thierry Volpiatto]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Thierry Volpiatto <thievol@posteo.net>
>> Cc: 68602@debbugs.gnu.org
>> Date: Sat, 20 Jan 2024 16:37:04 +0000
>> 
>> >> From: Thierry Volpiatto <thievol@posteo.net>
>> >> Date: Sat, 20 Jan 2024 05:56:11 +0000
>> >> 
>> >> 
>> >> Its read-language-name specify default in prompt but not as DEFAULT arg.
>> >
>> > Thanks.  But why is that a problem?
>> 
>> Because Helm needs this info to handle DEFAULT, it can't be aware of the
>> code running after the completing-read (read-language-name in this
>> case).
>
> Can you elaborate on this?  I don't think I follow (I don't use Helm).

When you press RET on an empty completing-read prompt and the function
provides a default, the completing-read returns this default.
When you run this function with helm-mode enabled, helm provide its
interface for completion on this completing-read and puts default on top
of its list to allow user pressing RET with an empty prompt to have this
default.  If the default arg is handled AFTER the completing-read helm
cannot guess what is it.

Example (selection is "|"):

(defun foo ()
  (let ((val (completing-read
              "test: " '("a" "b" "c" "d") nil nil nil nil "d")))
    val))

d|
a
b
c

(defun foo-1 ()
  (let ((val (completing-read "test: " '("a" "b" "c" "d"))))
    (if (string= val "") "d" val)))

a|
b
c
d

In `foo` and `foo-1` with helm-mode enabled and press RET with nothing
in prompt, helm will return "d" with `foo` but "a" with `foo-1`.

In `foo` helm is aware that "d" is the default, in `foo-1` it has no
ideas of what the default is even if `foo-1` code is as correct as `foo`. 

-- 
Thierry

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bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Thierry Volpiatto]

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Here a patch attached fixing this.

-- 
Thierry

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From 5eb0ec18cea14a8d5a13c8ae02223b67dbdc280c Mon Sep 17 00:00:00 2001
From: Thierry Volpiatto <thievol@posteo.net>
Date: Sun, 21 Jan 2024 19:13:59 +0100
Subject: [PATCH] Use DEFAULT arg of read-language-name (bug#68602)

in describe-language-environment.  This allows external packages
providing completion (helm etc...) to be aware of default easily.

* lisp/international/mule-cmds.el (describe-language-environment): Do it.
---
 lisp/international/mule-cmds.el | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lisp/international/mule-cmds.el b/lisp/international/mule-cmds.el
index 07f11a62594..7ae3bd7c816 100644
--- a/lisp/international/mule-cmds.el
+++ b/lisp/international/mule-cmds.el
@@ -2159,10 +2159,9 @@ See `set-language-info-alist' for use in programs."
   (interactive
    (list (read-language-name
 	  'documentation
-	  (format-prompt "Describe language environment" current-language-environment))))
+	  (format-prompt "Describe language environment" current-language-environment)
+          current-language-environment)))
   (let ((help-buffer-under-preparation t))
-    (if (null language-name)
-	(setq language-name current-language-environment))
     (if (or (null language-name)
 	    (null (get-language-info language-name 'documentation)))
 	(error "No documentation for the specified language"))
-- 
2.34.1


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bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Eli Zaretskii]

> From: Thierry Volpiatto <thievol@posteo.net>
> Cc: 68602@debbugs.gnu.org
> Date: Sun, 21 Jan 2024 18:26:47 +0000
> 
> Here a patch attached fixing this.

Thanks.  I decided to install only part of the patch, leaving the test
for nil alone, just to be on the safe side: with today's proliferation
of different completion schemes and packages, who knows what
read-language-name can yield?

having installed this on the master branch, I'm therefore closing the
bug.

bug#68602: 29.2; describe-language-environment fails to specify default in its CR

[Thierry Volpiatto]

[-- Attachment #1: Type: text/plain, Size: 657 bytes --]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Thierry Volpiatto <thievol@posteo.net>
>> Cc: 68602@debbugs.gnu.org
>> Date: Sun, 21 Jan 2024 18:26:47 +0000
>> 
>> Here a patch attached fixing this.
>
> Thanks.  I decided to install only part of the patch, leaving the test
> for nil alone, just to be on the safe side: with today's proliferation
> of different completion schemes and packages, who knows what
> read-language-name can yield?

Yes, if a package providing completion doesn't handle DEFAULT, indeed
the test is needed.

> having installed this on the master branch, I'm therefore closing the
> bug.

Thanks.

-- 
Thierry

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