bug#66678: 30.0.50; Tabs close erratically in text terminal

bug#66678: 30.0.50; Tabs close erratically in text terminal

[Petteri Hintsanen]

[-- Attachment #1: Type: text/plain, Size: 4471 bytes --]

I'm running Emacs in xterm with xterm-mouse-mode and tab-bar-mode
enabled.  There, tabs have an "x" mark for closing them.  However, tabs
will also close if you click on the character position right after the
buffer name in the tab.  This makes it easy to unintentionally close a
tab instead of switching to it, which is very annoying.

Recipe:

- In xterm, start emacs by `emacs -Q -nw'.
- M-x xterm-mouse-mode
- M-x tab-bar-mode
- Create a new tab by clicking on "+" on the tab bar.
  Now you should have two tabs named `*scratch*'
- Click on the first (leftmost) tab right after the second asterisk.

Expected behavior: Leftmost tab is selected.
Actual behavior: Leftmost tab is closed.

I traced the issue to `tab-bar-auto-width' function which — I think — is
used to pad a tab text with spaces to make it have a uniform width
within the tab bar.  The function erroneously copies 'close-tab text
property from the close button text (tab-bar-close-button) and positions
it right after the buffer name, causing the said behavior.

The attached patch fixes the immediate issue, but I doubt if it is
sufficient, given that there is similar close tab-related logic elsewhere
in the code.  Another workaround is to set `tab-bar-close-button' to one
character string "x" instead of " x".


In GNU Emacs 30.0.50 (build 4, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.16.0) of 2023-10-22 built on romeo
Repository revision: ae337884107c4d5f66aaceef0e8b548565317412
Repository branch: master
System Description: Debian GNU/Linux 12 (bookworm)

Configured features:
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X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LC_MESSAGES: en_US.UTF-8
  value of $LANG: fi_FI.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  xterm-mouse-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  tab-bar-mode: t
  menu-bar-mode: t
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  global-font-lock-mode: t
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  minibuffer-regexp-mode: t
  line-number-mode: t
  indent-tabs-mode: t
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  auto-compression-mode: t

Load-path shadows:
None found.

Features:
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[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: Tab bar patch --]
[-- Type: text/x-diff, Size: 747 bytes --]

diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
index d2815c03ebf..e21367255a0 100644
--- a/lisp/tab-bar.el
+++ b/lisp/tab-bar.el
@@ -1227,7 +1227,9 @@ tab-bar-auto-width
                    ((< prev-width width)
                     (let* ((space (apply #'propertize " "
                                          (text-properties-at 0 name)))
-                           (ins-pos (- len (if close-p 1 0)))
+                           (ins-pos (- len (if close-p
+                                               (length tab-bar-close-button)
+                                             0)))
                            (prev-name name))
                       (while continue
                         (setq name (concat (substring name 0 ins-pos)

bug#66678: 30.0.50; Tabs close erratically in text terminal

[Eli Zaretskii]

> From: Petteri Hintsanen <petterih@iki.fi>
> Date: Sun, 22 Oct 2023 14:21:16 +0300
> 
> I'm running Emacs in xterm with xterm-mouse-mode and tab-bar-mode
> enabled.  There, tabs have an "x" mark for closing them.  However, tabs
> will also close if you click on the character position right after the
> buffer name in the tab.  This makes it easy to unintentionally close a
> tab instead of switching to it, which is very annoying.
> 
> Recipe:
> 
> - In xterm, start emacs by `emacs -Q -nw'.
> - M-x xterm-mouse-mode
> - M-x tab-bar-mode
> - Create a new tab by clicking on "+" on the tab bar.
>   Now you should have two tabs named `*scratch*'
> - Click on the first (leftmost) tab right after the second asterisk.
> 
> Expected behavior: Leftmost tab is selected.
> Actual behavior: Leftmost tab is closed.

This is not specific to xterm or xterm-mouse, it happens with any
mouse-equipped text-mode terminal.  It happens in Emacs 29 as well.

> I traced the issue to `tab-bar-auto-width' function which — I think — is
> used to pad a tab text with spaces to make it have a uniform width
> within the tab bar.  The function erroneously copies 'close-tab text
> property from the close button text (tab-bar-close-button) and positions
> it right after the buffer name, causing the said behavior.
> 
> The attached patch fixes the immediate issue, but I doubt if it is
> sufficient, given that there is similar close tab-related logic elsewhere
> in the code.  Another workaround is to set `tab-bar-close-button' to one
> character string "x" instead of " x".

Juri, please install the fix you think is appropriate on the emacs-29
branch, since the problem exists there as well.

Thanks.

bug#66678: 30.0.50; Tabs close erratically in text terminal

[Juri Linkov]

close 66678 29.1.90
thanks

> - Create a new tab by clicking on "+" on the tab bar.
>   Now you should have two tabs named `*scratch*'
> - Click on the first (leftmost) tab right after the second asterisk.
>
> Expected behavior: Leftmost tab is selected.
> Actual behavior: Leftmost tab is closed.
>
> I traced the issue to `tab-bar-auto-width' function which — I think — is
> used to pad a tab text with spaces to make it have a uniform width
> within the tab bar.  The function erroneously copies 'close-tab text
> property from the close button text (tab-bar-close-button) and positions
> it right after the buffer name, causing the said behavior.
>
> The attached patch fixes the immediate issue, but I doubt if it is
> sufficient, given that there is similar close tab-related logic elsewhere
> in the code.  Another workaround is to set `tab-bar-close-button' to one
> character string "x" instead of " x".

Thank you for finding this subtle bug and fixing it.
The space before "x" was intended to give more space to click
on the close button, i.e. for more wider clicking area.
So better to keep the 'close-tab' text property on the space.
This means that your patch is the right way to fix this.
Now it's pushed to the emacs-29 branch as well as separately
to master to avoid merge conflicts.