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

[Dmitry Gutov <dgutov@yandex.ru>]

On 10/17/17 5:34 AM, Eli Zaretskii wrote:

>> Should I always use (+ 2 (line-number-display-width)) instead?
> 
> If you need it in columns, yes.  This is for consistency with the
> value of display-line-numbers-width, which you can set.
>
>> That would be the actual amount of "screen estate used up for
>> line-number display".
>>
>> Can I rely on the extra value always being 2?
> 
> As long as we don't change the implementation, yes.  Alternatively,
> you can call line-number-display-width with the optional argument and
> get the result in pixels, in which case it includes everything (you
> can divide by frame-char-width to get the result back in columns).

Thanks, but isn't that more inconsistent? I would expect both return 
values of this function to measure the same thing, and there's nothing 
in the docstring to explain that difference.

On the other hand, the return value of the function can differ from what 
a variable is set to.

I guess I could live with that, but the function's docstring needs updating.