bug#29597: 26.0.90; line-number-display-width returns incorrect width

[Noam Postavsky <npostavs@users.sourceforge.net>]

On Fri, Dec 8, 2017 at 10:01 AM, Eli Zaretskii <eliz@gnu.org> wrote:

>> I understand that this function is also used internally for specific purposes, so it needs to behave a specific way to appease the initial writer of the code. But for the sake of sanity, I strongly suggest either fixing this function or creating a separate “public” function that operates vaguely in line with user expectation for those of us wanting to accommodate display-line-numbers-mode.
>
> Sorry, I don't understand what is missing.  If you wanted the value of
> 4 in your case, you need to call this function like this:
>
>   (line-number-display-width 'columns)
>
> as documented.

I think the idea would to split that function into 2 simpler ones, e.g.:

(line-number-display-columns) => 4
(line-number-display-width) => 2
(line-number-display-width t) => the equivalent in pixels