bug#64121: 28.2; C-SPC not working in term char mode

bug#64121: 28.2; C-SPC not working in term char mode

[Al Petrofsky]

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   emacs-28.2 -Q
   M-x term RET RET
   C-SPC

This should send an ASCII NUL (a zero byte) to the pty, but instead it
displays "Mark set" in the echo area.

To fix it, C-SPC needs to get special handling akin to the handling of
C-/.  Here's a patch that also makes C-M-SPC and C-M-/ work.

--- term.el 2022-09-06 17:31:54.000000000 -0400
+++ term-c-spc-fixed.el 2023-06-15 11:21:41.780140053 -0400
@@ -916,6 +916,9 @@
     (define-key map [next] 'term-send-next)
     (define-key map [xterm-paste] #'term--xterm-paste)
     (define-key map [?\C-/] #'term-send-C-_)
+    (define-key map [?\C- ] #'term-send-C-@)
+    (define-key map [?\C-\M-/] #'term-send-C-M-_)
+    (define-key map [?\C-\M- ] #'term-send-C-M-@)
     map)
   "Keyboard map for sending characters directly to the inferior process.")

@@ -1359,6 +1362,9 @@
 (defun term-send-del   () (interactive) (term-send-raw-string "\e[3~"))
 (defun term-send-backspace  () (interactive) (term-send-raw-string "\C-?"))
 (defun term-send-C-_  () (interactive) (term-send-raw-string "\C-_"))
+(defun term-send-C-@  () (interactive) (term-send-raw-string "\C-@"))
+(defun term-send-C-M-_  () (interactive) (term-send-raw-string "\e\C-_"))
+(defun term-send-C-M-@  () (interactive) (term-send-raw-string "\e\C-@"))

 (defun term-char-mode ()
   "Switch to char (\"raw\") sub-mode of term mode.

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bug#64121: 28.2; C-SPC not working in term char mode

[Eli Zaretskii]

> From: Al Petrofsky <al@petrofsky.org>
> Date: Fri, 16 Jun 2023 20:06:57 -0400
> 
>    emacs-28.2 -Q
>    M-x term RET RET
>    C-SPC
> 
> This should send an ASCII NUL (a zero byte) to the pty, but instead it
> displays "Mark set" in the echo area.

I cannot reproduce this here: I don't see "Mark set" in the echo area.

Maybe this somehow depends on the terminal emulator?  (I use PuTTY.)

How to verify that the null character is sent to the pty?

bug#64121: 28.2; C-SPC not working in term char mode

[Al Petrofsky]

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On Sat, Jun 17, 2023 at 2:12 AM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Al Petrofsky <al@petrofsky.org>
> > Date: Fri, 16 Jun 2023 20:06:57 -0400
> >
> >    emacs-28.2 -Q
> >    M-x term RET RET
> >    C-SPC
> >
> > This should send an ASCII NUL (a zero byte) to the pty, but instead it
> > displays "Mark set" in the echo area.
>
> I cannot reproduce this here: I don't see "Mark set" in the echo area.
>
> Maybe this somehow depends on the terminal emulator?  (I use PuTTY.)
>

I should have mentioned this bug won't show up if emacs is running in a
tty. The bug
stems from the subtle difference between C-SPC and C-@ input events on
graphical
terminals.  On a tty, C-SPC and C-@ become the same thing before they get
to emacs.


> How to verify that the null character is sent to the pty?
>

You can start an emacs -nw inside the term. Then pressing C-SPC should
result in a "Mark set" in the inner emacs's echo area.

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bug#64121: 28.2; C-SPC not working in term char mode

[Eli Zaretskii]

> From: Al Petrofsky <al@petrofsky.org>
> Date: Sat, 17 Jun 2023 02:26:40 -0400
> Cc: 64121@debbugs.gnu.org
> 
> On Sat, Jun 17, 2023 at 2:12 AM Eli Zaretskii <eliz@gnu.org> wrote:
> 
>  > From: Al Petrofsky <al@petrofsky.org>
>  > Date: Fri, 16 Jun 2023 20:06:57 -0400
>  >
>  >    emacs-28.2 -Q
>  >    M-x term RET RET
>  >    C-SPC
>  >
>  > This should send an ASCII NUL (a zero byte) to the pty, but instead it
>  > displays "Mark set" in the echo area.
> 
>  I cannot reproduce this here: I don't see "Mark set" in the echo area.
> 
>  Maybe this somehow depends on the terminal emulator?  (I use PuTTY.)
> 
> I should have mentioned this bug won't show up if emacs is running in a tty. The bug
> stems from the subtle difference between C-SPC and C-@ input events on graphical
> terminals.  On a tty, C-SPC and C-@ become the same thing before they get to emacs.

Then I'm afraid I cannot evaluate this bug and its proposed solution,
as I don't have access to a platform where I can run a GUI Emacs with
"M-x term" still supported.

Could someone else please reproduce this and review the proposed
changes?  TIA.

bug#64121: 28.2; C-SPC not working in term char mode

[Gregory Heytings]

>
> Could someone else please reproduce this and review the proposed 
> changes?  TIA.
>

I can reproduce this (with Emacs 29), and the proposed changes LGTM.

bug#64121: 28.2; C-SPC not working in term char mode

[Eli Zaretskii]

> Date: Sat, 17 Jun 2023 07:08:25 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: Al Petrofsky <al@petrofsky.org>, 64121@debbugs.gnu.org
> 
> > Could someone else please reproduce this and review the proposed 
> > changes?  TIA.
> 
> I can reproduce this (with Emacs 29), and the proposed changes LGTM.

Thanks, installed on the master branch, and closing the bug.