Subject: Re: bug#59311: 29.0.50; tab-bar global-mode-string affected by global-display-line-numbers

From: Juri Linkov <[email-masked]>
Date: Fri, 18 Nov 2022 09:15:02 +0200

> 2) Eval the following to enable global-display-line-numbers-mode:
>
> (progn
>   (global-display-line-numbers-mode 1))
> ...
> Result: the global-mode-line is displayed in the tab-bar, right-aligned,
> with an incorrect padding on the right. See attached video.

Thanks for the bug report.  Here is a possible fix
to get the correct pixel width without taking into account
line numbers inserted to the text area of the same buffer:

diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 6e4d88b4df..92bbdfaa9c 100644
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -322,6 +322,8 @@ string-pixel-width
     ;; Keeping a work buffer around is more efficient than creating a
     ;; new temporary buffer.
     (with-current-buffer (get-buffer-create " *string-pixel-width*")
+      (when display-line-numbers-mode
+        (display-line-numbers-mode -1))
       (delete-region (point-min) (point-max))
       (insert string)
       (car (buffer-text-pixel-size nil nil t)))))

But really I think the bug is in global-display-line-numbers-mode.
Maybe it should not enable display-line-numbers-mode
in internal buffers whose names start with a space?

For example, here is what tab-line-mode--turn-on does:

  (defun tab-line-mode--turn-on ()
    (unless (or (minibufferp)
                (string-match-p "\\` " (buffer-name))
                (memq major-mode tab-line-exclude-modes)
                (get major-mode 'tab-line-exclude)
                (buffer-local-value 'tab-line-exclude (current-buffer)))
      (tab-line-mode 1)))

But display-line-numbers--turn-on is only:

  (defun display-line-numbers--turn-on ()
    (unless (minibufferp)
      (display-line-numbers-mode)))

I think we should add at least (string-match-p "\\` " (buffer-name))
to display-line-numbers--turn-on.