bug#67248: 30.0.50; string-pixel-width is affected by the global value of display-line-numbers

[Dmitry Gutov <dgutov@yandex.ru>]

1. (string-pixel-width "abc") ; => 51
2. (customize-set-variable 'display-line-numbers t)
3. (string-pixel-width "abc") ; => 119

This function's implementation makes provision for
display-line-numbers-mode, but not for the original variable
display-line-numbers, which will be t independent of the value of
display-line-numbers-mode.

I think it's a bad idea to have these two different ways to do the same
thing, and it can lead to bugs like this one. I would suggest obsoleting
the public use of display-line-numbers -- making it private, probably.
At least removing it from the customization group display-line-numbers.

Barring that, the patch below seems to work.  Although it proliferates
the differences between Emacs versions which one would have to be on the
lookout for.

Originally reported at
https://github.com/company-mode/company-mode/issues/1427.

diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 572822351b1..4fda98ae3d0 100644
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -343,8 +343,7 @@ string-pixel-width
      (with-current-buffer (get-buffer-create " *string-pixel-width*")
        ;; If `display-line-numbers-mode' is enabled in internal
        ;; buffers, it breaks width calculation, so disable it (bug#59311)
-      (when (bound-and-true-p display-line-numbers-mode)
-        (display-line-numbers-mode -1))
+      (setq-local display-line-numbers nil)
        (delete-region (point-min) (point-max))
        ;; Disable line-prefix and wrap-prefix, for the same reason.
        (setq line-prefix nil


In GNU Emacs 30.0.50 (build 271, x86_64-pc-linux-gnu, GTK+ Version
  3.24.34, cairo version 1.16.0) of 2023-11-17 built on potemkin
Repository revision: 94849ba35f40393362050b5937578dcf3076b4bf
Repository branch: feature/cl-lib-improvements
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Ubuntu 22.10