bug#73005: [REGRESSION, BISECTED]: line numbers disappear when pressing `df` in evil-mode

[David Ponce]

I forgot to reply to all. Sorry.
 
On 04/11/2024 5:38 PM, Eli Zaretskii wrote:
> > Date: Mon, 4 Nov 2024 14:58:09 +0100
> > Cc: Hi-Angel@yandex.ru, 73005@debbugs.gnu.org
> > From: David Ponce <da_vid@orange.fr>
> >
> > > > 2024-11-04  David Ponce  <da_vid@orange.fr>
> > > >
> > > >         * subr-x.el (string-pixel-width): Set text property
> > > >         `display-line-numbers-disable' instead of changing the
> > > >         buffer-local value of `display-line-numbers'.  Fix bug#73005.
> > >
> > > Thanks, I will look into this when I have time.  It isn't urgent.
> >
> > No problem for me.  At the same time, maybe you can shed some light
> > on why initializing the local variable `display-line-numbers' in the
> > work buffer interferes with the setting in other buffer?  I'm probably
> > missing something in the current implementation.
>
> Without looking at the code, my first guess would be that you change
> the global default value, not the buffer-local value.  The fact that
> you kill-all-local-variables might have something to do with that.

I cannot see where it could happen in the code.

However, I think I have more or less figured out what could be going on.

`display-line-numbers' is a special variable that when changed causes the
current buffer to be redisplayed in the current window (see frame.el from
line 3194).

It seems that, when `string-pixels-width' sets the value of
`display-line-numbers' to nil locally in the working buffer, this triggers
a redisplay of the buffer in the selected window, and the line numbers to
disappear.  When the working buffer is later recycled and local variables
killed, it seems that this does not trigger buffer redisplay, and the line
numbers therefore remain disabled, as observed in the simple recipe provided
by Konstantin.  If you just evaluate (setq display-line-numbers 
display-line-numbers)
after Konstantin's recipe, the current buffer is redisplayed and the line
numbers appear again, because `string-pixel-width' didn't change the global 
value
of `display-line-numbers'.

If I modify `string-pixel-width' to add
`(setq display-line-numbers display-line-numbers)' before to return the result,
line numbers are not deactivated:

(defun string-pixel-width (string &optional buffer)
  "Return the width of STRING in pixels.
If BUFFER is non-nil, use the face remappings from that buffer when
determining the width.
If you call this function to measure pixel width of a string
with embedded newlines, it returns the width of the widest
substring that does not include newlines."
  (declare (important-return-value t))
  (if (zerop (length string))
      0
    ;; Keeping a work buffer around is more efficient than creating a
    ;; new temporary buffer.
    (prog1
        (with-work-buffer
      ;; If `display-line-numbers' is enabled in internal
      ;; buffers (e.g. globally), it breaks width calculation
      ;; (bug#59311).  Disable `line-prefix' and `wrap-prefix',
      ;; for the same reason.
      (setq display-line-numbers nil
            line-prefix nil wrap-prefix nil)
      (if buffer
          (setq-local face-remapping-alist
                      (with-current-buffer buffer
                        face-remapping-alist))
        (kill-local-variable 'face-remapping-alist))
      ;; Avoid deactivating the region as side effect.
      (let (deactivate-mark)
        (insert string))
      ;; Prefer `remove-text-properties' to `propertize' to avoid
      ;; creating a new string on each call.
      (remove-text-properties
       (point-min) (point-max) '(line-prefix nil wrap-prefix nil))
      (car (buffer-text-pixel-size nil nil t)))
      (setq display-line-numbers display-line-numbers))))

However, using the `display-line-numbers-disable' property to temporarily
disable line numbers in `string-pixels-width', without involving redisplay,
seems a better approach to me.

Regarding Konstantin recipe, `string-pixel-width' is called by 
`tab-bar-auto-width'
when (lookup-key global-map [tab-bar]) is evaluated.

Thanks