bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Khoa Vo]

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Note: I have repoduced this bug even without a configuration file.

Steps:
- Enter term-mode.
- Enter term-line-mode.
- Type a command one line below the prompt, but don't hit "enter" yet.
- Issue command "M-x split-window-right".
- You can see the problem: one or more new lines are inserted after the
prompt.
  Pushing the command further down.

This is problematic because:
- If you repeat that enough times, you can't see the command anymore.
- I need the end of the buffer to be where the prompt is,
  so I can get to the prompt quickly.
- Also I sometimes need to copy the command, I can just copy from the
  prompt to the end of the buffer.

It seems to me like the issue is with splitting the window.

In GNU Emacs 27.2 (build 1, x86_64-apple-darwin18.7.0, NS appkit-1671.60
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bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Lars Ingebrigtsen]

Khoa Vo <vodangkhoa873@gmail.com> writes:

> Note: I have repoduced this bug even without a configuration file.
>
> Steps:
> - Enter term-mode.
> - Enter term-line-mode.
> - Type a command one line below the prompt, but don't hit "enter" yet.
> - Issue command "M-x split-window-right".
> - You can see the problem: one or more new lines are inserted after the prompt.
>   Pushing the command further down.

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

I'm not sure I understand the problem.  If by "Enter term-mode" you mean
`M-x term RET RET', then commands like `M-x split-window-right' aren't
available, so perhaps you mean something else?

Can you give a step-by-step recipe to reproduce the problem, starting
from "emacs -Q"?

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

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Robert Pluim]

>>>>> On Mon, 11 Jul 2022 16:42:01 +0200, Lars Ingebrigtsen <larsi@gnus.org> said:

    Lars> Khoa Vo <vodangkhoa873@gmail.com> writes:
    >> Note: I have repoduced this bug even without a configuration file.
    >> 
    >> Steps:
    >> - Enter term-mode.
    >> - Enter term-line-mode.
    >> - Type a command one line below the prompt, but don't hit "enter" yet.
    >> - Issue command "M-x split-window-right".
    >> - You can see the problem: one or more new lines are inserted after the prompt.
    >> Pushing the command further down.

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

    Lars> I'm not sure I understand the problem.  If by "Enter term-mode" you mean
    Lars> `M-x term RET RET', then commands like `M-x split-window-right' aren't
    Lars> available, so perhaps you mean something else?

    Lars> Can you give a step-by-step recipe to reproduce the problem, starting
    Lars> from "emacs -Q"?

M-x term
C-c C-j
C-n
ls C-x 3

reproduces for me (you can run any normal Emacs command when youʼre in term-line-mode)

Robert
-- 

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Michael Heerdegen]

Robert Pluim <rpluim@gmail.com> writes:

> M-x term
> C-c C-j
> C-n
> ls C-x 3

Happens even without C-n:

M-x term
C-c C-j
ls
C-x 2     ;; a linefeed between prompt and "ls" in inserted
C-x 1     ;; another one is inserted

Michael.

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Lars Ingebrigtsen]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> Happens even without C-n:
>
> M-x term
> C-c C-j
> ls
> C-x 2     ;; a linefeed between prompt and "ls" in inserted
> C-x 1     ;; another one is inserted

Thanks.  I've had a brief look at term.el to see what could be causing
this -- I wondered whether it might be a window change hook or
something, but that doesn't seem to be the case.

It seems to be happening non-synchronously -- sometimes the extra
newline isn't added until half a second passes, so perhaps it's
something that happens during communication between the shell and Emacs.

I'm pretty unfamiliar with the term.el code.  Anybody know where to
start poking?

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

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

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

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Lars Ingebrigtsen <larsi@gnus.org> writes:

> Michael Heerdegen <michael_heerdegen@web.de> writes:
>
>> Happens even without C-n:
>>
>> M-x term
>> C-c C-j
>> ls
>> C-x 2     ;; a linefeed between prompt and "ls" in inserted
>> C-x 1     ;; another one is inserted
>
> Thanks.  I've had a brief look at term.el to see what could be causing
> this -- I wondered whether it might be a window change hook or
> something, but that doesn't seem to be the case.
>
> It seems to be happening non-synchronously -- sometimes the extra
> newline isn't added until half a second passes, so perhaps it's
> something that happens during communication between the shell and Emacs.
>
> I'm pretty unfamiliar with the term.el code.  Anybody know where to
> start poking?

When a term.el window is resized, emacs sends a SIGWINCH to it's
process. Bash seems to output some spaces newlines upon receiving a
SIGWINCH. In an ordinary terminal emulator, these spaces have the effect
of clearing bash's readline display and they aren't really visible to
the user. In term.el, however, they are inserted before the "ls" that
the user has input (this "ls" is input in term-line-mode, which means
that bash isn't aware of it yet, until the user presses RET).

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bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Michael Heerdegen]

miha@kamnitnik.top writes:

> When a term.el window is resized, emacs sends a SIGWINCH to it's
> process. Bash seems to output some spaces newlines upon receiving a
> SIGWINCH.

I tried with a different shell: using "dash" (default system
shell in Debian) the problem is not reproducible.

Michael.

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Eli Zaretskii]

> Cc: Robert Pluim <rpluim@gmail.com>, 48399@debbugs.gnu.org,
>  Khoa Vo <vodangkhoa873@gmail.com>
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Tue, 12 Jul 2022 14:28:45 +0200
> 
> Michael Heerdegen <michael_heerdegen@web.de> writes:
> 
> > Happens even without C-n:
> >
> > M-x term
> > C-c C-j
> > ls
> > C-x 2     ;; a linefeed between prompt and "ls" in inserted
> > C-x 1     ;; another one is inserted
> 
> Thanks.  I've had a brief look at term.el to see what could be causing
> this -- I wondered whether it might be a window change hook or
> something, but that doesn't seem to be the case.
> 
> It seems to be happening non-synchronously -- sometimes the extra
> newline isn't added until half a second passes, so perhaps it's
> something that happens during communication between the shell and Emacs.
> 
> I'm pretty unfamiliar with the term.el code.  Anybody know where to
> start poking?

I think it's because we call set-process-window-size, which sends an
IOCTL to the shell.

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Andreas Schwab]

On Jul 12 2022, miha--- via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:

> When a term.el window is resized, emacs sends a SIGWINCH to it's
> process. Bash seems to output some spaces newlines upon receiving a
> SIGWINCH.

That doesn't happen though when just sending SIGWINCH to the shell.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Andreas Schwab]

On Jul 12 2022, Lars Ingebrigtsen wrote:

> I'm pretty unfamiliar with the term.el code.  Anybody know where to
> start poking?

strace tells that the shell, upon receiving SIGWINCH and noticing a
changed terminal size, redraws the prompt preceeded by a CR CSI K CR
sequence.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Andreas Schwab]

You can reproduce that by just printing "\e[K" to the terminal, which is
handled by term-erase-in-line.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

bug#48399: 27.2; term-mode: After splitting window, newlines are inserted

[Lars Ingebrigtsen]

Andreas Schwab <schwab@suse.de> writes:

> You can reproduce that by just printing "\e[K" to the terminal, which is
> handled by term-erase-in-line.

Thanks.  I can confirm that the newline is added by
term-erase-in-line -- the following makes the problem go away:

diff --git a/lisp/term.el b/lisp/term.el
index a28d8c5d76..3a9d41ffc1 100644
--- a/lisp/term.el
+++ b/lisp/term.el
@@ -3979,7 +3979,7 @@ term-erase-in-line
       ;; extra space when wrapped is false.
       (when wrapped
 	(insert ? ))
-      (insert ?\n)
+      ;;(insert ?\n)
       (put-text-property saved-point (point) 'font-lock-face 'default)
       (goto-char saved-point))))
 

But is obviously not the right thing...  But I guess it could be the
right thing if we only skip the newline insertion if we're at the
prompt?  (I don't know how to determine that, though.)

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