bug#56102: 29.0.50; fit-frame-to-buffer's window-text-pixel-size calculation can be incorrect when only is set to vertically

[Aaron Jensen <aaronjensen@gmail.com>]

On Wed, Jun 22, 2022 at 9:59 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Aaron Jensen <aaronjensen@gmail.com>
> > Date: Sun, 19 Jun 2022 23:03:14 -0400
> >
> >
> > To repro, open emacs -Q and resize your frame so that the ";; This
> > buffer..." text wraps (this repro assumes your monitor has more than
> > enough space for it to not wrap if the frame was big enough).
> >
> > Add a few more lines of text and then:
> >
> > M-: (fit-frame-to-buffer nil nil nil nil nil 'vertically)
> >
> > You should see that the frame's height is too short and does not contain
> > all the lines. It contains one fewer line for each wrapped line.
> >
> > Screenshots:
> >
> > https://share.cleanshot.com/huexHe
> > https://share.cleanshot.com/dnhKex
> >
> > The problem appears to be the lines:
> >
> > (size
> >             (window-text-pixel-size window from to max-width max-height))
> >
> > As the max-width will be larger than the current frame (meaning the
> > height calculation will not take wrapping into account).
> >
> > One possible fix is to set min/max height/width based on `only' to
> > (frame-parameter frame 'width) / (frame-parameter frame 'height) but I
> > do not know if that is the best fix.
> >
> > If that is done, then it may be possible to remove the rest of the
> > special handling for `only' that sets width/height to nil and handles that.
>
> I think you're right, but I'd like to hear if Martin has any comments.

Sounds good. The most minimal change I can think of is to use the
current frame's width as max-width in the window-text-pixel-size call
when only is set to vertically. I don't know of any reason we need to
constrain max-height in that call because it doesn't have the same
impact. That can be done either explicitly in that call or by changing
max-width to be set to the current width as I described before. That
would be asymmetrical with max-height though, which would be rather
confusing IMO.

Aaron