bug#28248: 26.0.50; display-line-numbers does not affect window-width / window-text-width

[Stephen Berman <stephen.berman@gmx.net>]

On Sun, 27 Aug 2017 17:40:04 +1200 Steve Purcell <steve@sanityinc.com> wrote:

> When display-line-numbers mode is enabled, this has no effect on the
> return value of window-width or window-text-width, and there is also no
> variable which contains the current width of the line numbers. This all
> means there is no way to determine the width of the text area of the
> window.
>
> This concretely matters to me because my package "page-break-lines"
> remaps the display table of ^L to a horizontal line the width of the
> window: this technique is based on prior art.

The display of the line separating todo and done items in Todo mode
(part of Emacs) is also affected by this.  (However, with the default
setup of Todo mode displaying line numbers is unnecessary and even
distracting, since Todo mode already numbers the items by default.)

> I note that turning off fringes *does* correctly adjust
> window-text-width, so it seems that display-line-numbers-mode should do
> the same.

I never tried that before with Todo mode but did just now and see that
it doesn't quite work here: the left side is fine but on the right there
is a continuation character in the last column, so the separator line
breaks on the last character (this is with overflow-newline-into-fringe
set to t, the default).

Steve Berman