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 7:33 PM, Eli Zaretskii wrote:

> They are used for 2 different purposes, which are contradictory to
> some degree.

But that's true for all core functions with a PIXELWISE argument, isn't 
it? Yet, the rest measure the same thing in both cases, AFAIK.

> The value in column units is primarily meant to be used
> for setting display-line-numbers-width (see, e.g., how
> display-line-numbers.el uses that), and also for users, so burdening
> them with anything that is not directly related to the value of the
> largest visible line number would be a nuisance.

Maybe display-line-numbers-width could include the separator columns as 
well.

> OTOH, the
> column-unit value is of limited utility for layout calculations,
> because the columns are of the line-number face, which could be
> smaller or larger than the default face.

That changes little for me: overlay-based layout can't do anything with 
pixels anyway. If all I can do is divine the resulting value by 
frame-char-width and hope for the best, I might as well use the return 
value in columns to begin with.

Furthermore, in Company, we already call similar functions (like 
window-body-height) with PIXELWISE nil.

> Therefore, layout
> calculations should use the function's pixelwise variety, and convert
> into columns by dividing by the width of the font used for buffer
> text.  (Which btw means my response to you earlier -- see above -- was
> incomplete: you should use the function in pixel-unit mode, if you
> need to account for the screen space eaten by line numbers, and then
> you don't have to add anything to the value it returns.)

I can't help but worry about how an off-by-one error in pixel width 
(which is not strictly defined) would result in an off-by-one error in 
column width after division. And again, I'm in no position to use the 
pixelwise value.

>> On the other hand, the return value of the function can differ from what
>> a variable is set to.
> 
> I think that'd be a nuisance; again, see what display-line-numbers.el
> does.
> 
> I agree that this is not ideal, to say the least, but I hope you at
> least understand the issues now.  If there's a better solution, I'm
> all ears.

display-line-numbers-update-width might look worse, I agree. But we 
could have two functions, right? Both line-number-display-width and 
display-line-numbers-update-width could delegate to 
line-number-display-inner-width.

Just a suggestion.

>> the function's docstring needs updating.
> 
> Done.

Thank you.

> P.S. I'd still like to hear your opinions on the related questions I
> asked here:
> 
>    https://debbugs.gnu.org/cgi/bugreport.cgi?bug=28855#8

Sorry, I haven't noticed your question, and I don't know what :align-to 
is about. And to be frank, I don't understand that question now.

I'll try to re-read and respond.