bug#23204: 25.1.50; Strange behaviour of ‘read-char’

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Mark Karpov]

I'm not sure if it's sort of feature (rather undocumented) or a bug.
Let's say I have a command that uses ‘read-char’ repeatedly, and it's
given a custom prompt as the first argument, like this:

  (defun my-command ()
    (interactive)
    (while (read-char "My prompt…" t)))

Now if you call this from lisp or like this: ‘M-x my-command RET’,
everything is fine: you see the prompt and you can type some chars
(press ‘C-g’ to get out of this).

But if you bind the command to key sequence, like this:

  (global-set-key (kbd "<menu> t y") #'my-command)

Then you have a nasty problem when you actually call it. Try to call it
and then type some characters — you will see no prompt and they will
accumulate in echo area indefinitely:

  menu t y h e r e SPC I SPC t y p e SPC t h i n g s SPC a n d SPC i t
  SPC i s SPC g e t t i n g SPC r a t h e r SPC l o n g

Does this work as intended? I would like to continue using ‘read-char’,
is there a way to just display my prompt in this case as well?



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bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Eli Zaretskii]

> From: Mark Karpov <markkarpov@openmailbox.org>
> Date: Sun, 03 Apr 2016 16:32:33 +0600
> 
>   (defun my-command ()
>     (interactive)
>     (while (read-char "My prompt…" t)))
> 
> Now if you call this from lisp or like this: ‘M-x my-command RET’,
> everything is fine: you see the prompt and you can type some chars
> (press ‘C-g’ to get out of this).
> 
> But if you bind the command to key sequence, like this:
> 
>   (global-set-key (kbd "<menu> t y") #'my-command)
> 
> Then you have a nasty problem when you actually call it. Try to call it
> and then type some characters — you will see no prompt and they will
> accumulate in echo area indefinitely:
> 
>   menu t y h e r e SPC I SPC t y p e SPC t h i n g s SPC a n d SPC i t
>   SPC i s SPC g e t t i n g SPC r a t h e r SPC l o n g

What if you do this instead:

  (global-set-key (kbd "<f8>") #'my-command)

Does this work as expected?  If so, does that explain what happens in
your original example?

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Mark Karpov]

This works, but I do not see how it explains this behavior. IMO, the
prompt should appear no matter how the command is invoked, because that
prompt is part of that command's functioning.

Eli Zaretskii writes:

> What if you do this instead:
>
>   (global-set-key (kbd "<f8>") #'my-command)
>
> Does this work as expected?  If so, does that explain what happens in
> your original example?

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Noam Postavsky]

severity 23204 minor
quit

I also don't quite understand why this happens, but it seems that
using (message nil) to clear the minibuffer also works:

(defun my-command ()
  (interactive)
  (message nil)
  (while (read-char "My prompt…" t)))

(global-set-key (kbd "<f12> t y") #'my-command)

(I can't bind <menu> t y in emacs -Q, I get an error message telling
me <menu> is not a prefix key)

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Sun, 12 Jun 2016 13:02:30 -0400
> Cc: Mark Karpov <markkarpov@openmailbox.org>
> 
> I also don't quite understand why this happens, but it seems that
> using (message nil) to clear the minibuffer also works:
> 
> (defun my-command ()
>   (interactive)
>   (message nil)
>   (while (read-char "My prompt…" t)))
> 
> (global-set-key (kbd "<f12> t y") #'my-command)
> 
> (I can't bind <menu> t y in emacs -Q, I get an error message telling
> me <menu> is not a prefix key)

I think the problem is specifically with invoking such commands via
menus, and the reason is that menu handling is inside the toolkit, out
of Emacs control.

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Noam Postavsky]

On Sun, Jun 12, 2016 at 1:11 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> I think the problem is specifically with invoking such commands via
> menus, and the reason is that menu handling is inside the toolkit, out
> of Emacs control.

No, without the (message nil) I see the problem when binding to <f12> t y.

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Sun, 12 Jun 2016 13:13:09 -0400
> Cc: 23204@debbugs.gnu.org, Mark Karpov <markkarpov@openmailbox.org>
> 
> On Sun, Jun 12, 2016 at 1:11 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> > I think the problem is specifically with invoking such commands via
> > menus, and the reason is that menu handling is inside the toolkit, out
> > of Emacs control.
> 
> No, without the (message nil) I see the problem when binding to <f12> t y.

Because F12 is not a prefix key.

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Noam Postavsky]

On Sun, Jun 12, 2016 at 1:17 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Noam Postavsky <npostavs@users.sourceforge.net>
>> Date: Sun, 12 Jun 2016 13:13:09 -0400
>> Cc: 23204@debbugs.gnu.org, Mark Karpov <markkarpov@openmailbox.org>
>>
>> On Sun, Jun 12, 2016 at 1:11 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> > I think the problem is specifically with invoking such commands via
>> > menus, and the reason is that menu handling is inside the toolkit, out
>> > of Emacs control.
>>
>> No, without the (message nil) I see the problem when binding to <f12> t y.
>
> Because F12 is not a prefix key.

Ok, then I don't quite understand what you mean by "menus", I thought
that means the thing at the top of the screen that can be clicked with
the mouse.

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Sun, 12 Jun 2016 13:23:31 -0400
> Cc: 23204@debbugs.gnu.org, Mark Karpov <markkarpov@openmailbox.org>
> 
> On Sun, Jun 12, 2016 at 1:17 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> >> From: Noam Postavsky <npostavs@users.sourceforge.net>
> >> Date: Sun, 12 Jun 2016 13:13:09 -0400
> >> Cc: 23204@debbugs.gnu.org, Mark Karpov <markkarpov@openmailbox.org>
> >>
> >> On Sun, Jun 12, 2016 at 1:11 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> >> > I think the problem is specifically with invoking such commands via
> >> > menus, and the reason is that menu handling is inside the toolkit, out
> >> > of Emacs control.
> >>
> >> No, without the (message nil) I see the problem when binding to <f12> t y.
> >
> > Because F12 is not a prefix key.
> 
> Ok, then I don't quite understand what you mean by "menus"

Maybe nothing, if the OP's problem is also that <menu>, whatever it
is, is not a prefix key.

> I thought that means the thing at the top of the screen that can be
> clicked with the mouse.

Me too, but maybe I was just confused.

bug#23204: 25.1.50; Strange behaviour of ‘read-char’

[Lars Ingebrigtsen]

Mark Karpov <markkarpov@openmailbox.org> writes:

> I'm not sure if it's sort of feature (rather undocumented) or a bug.
> Let's say I have a command that uses ‘read-char’ repeatedly, and it's
> given a custom prompt as the first argument, like this:
>
>   (defun my-command ()
>     (interactive)
>     (while (read-char "My prompt…" t)))
>
> Now if you call this from lisp or like this: ‘M-x my-command RET’,
> everything is fine: you see the prompt and you can type some chars
> (press ‘C-g’ to get out of this).
>
> But if you bind the command to key sequence, like this:
>
>   (global-set-key (kbd "<menu> t y") #'my-command)
>
> Then you have a nasty problem when you actually call it. Try to call it
> and then type some characters — you will see no prompt and they will
> accumulate in echo area indefinitely:
>
>   menu t y h e r e SPC I SPC t y p e SPC t h i n g s SPC a n d SPC i t
>   SPC i s SPC g e t t i n g SPC r a t h e r SPC l o n g

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

I can reproduce this problem in Emacs 25.1, but not on the current
master, so it looks like it's been fixed in the years since this was
first reported, and I'm therefore closing this bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no