GNU bug report logs - #74091
31.0.50; string-pixel-width in mode line disables region

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Eshel Yaron <me <at> eshelyaron.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 31.0.50; string-pixel-width in mode line disables region
Date: Tue, 29 Oct 2024 18:27:05 +0100

The new implementation of string-pixel-width has some unexpected effect
when it is called from mode-line-format, as happens for example when
mode-line-format-right-align occurs in mode-line-format:

1. emacs -Q
2. (setq-default mode-line-format
	      '("" (:eval (progn (string-pixel-width "foo") nil))))
3. C-x C-f /path/to/emacs/lisp/subr.el
4. C-SPC
5. C-n

At this point the region is expected to be active since we activated it
in step 4.  But in step 5 the mode line is updated, which calls
string-pixel-width, which in turn unexpectedly disables the region.

I'm not really sure why this happens...  Also, if I now trace
string-pixel-width, then it no longer disables the region and everything
starts working as expected.


Thanks,

Eshel

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