bug#54894: 28.1; window-body-height returns wrong result if line-spacing is non-nil

[martin rudalics]

> Help for window-body-height says:
> (window-body-height &optional WINDOW PIXELWISE)
>
> Return the height of WINDOW’s text area.
> WINDOW must be a live window and defaults to the selected one.  Optional
> argument PIXELWISE non-nil means return the height of WINDOW’s text area
> in pixels.  The return value does not include the mode line or header
> line or any horizontal divider.
>
> If PIXELWISE is nil, return the largest integer smaller than WINDOW’s
> pixel height divided by the character height of WINDOW’s frame.  This
> means that if a line at the bottom of the text area is only partially
> visible, that line is not counted.
> ----------
>
> It seems the case with PIXELWISE being nil is not handled correctly when
> line-spacing is non-nil.

Line-spacing does not affect the "character height of WINDOW’s frame".
I have made local changes here that describe that function as follows:

 -- Function: window-body-height &optional window pixelwise
     This function returns the height of WINDOW’s body.  WINDOW must be
     a live window and defaults to the selected one.

     If the optional argument PIXELWISE is non-‘nil’, this function
     returns the height of WINDOW’s body in pixels—the body pixel height
     of WINDOW.

     If PIXELWISE is ‘nil’, the return value depends on the current
     value of ‘window-scale-body’ (*note Window Character Size::) as
     follows:

        • If ‘window-scale-body’ is ‘nil’, this function returns the
          largest integer smaller than WINDOW’s body pixel height
          divided by the character height of WINDOW’s frame.

        • If ‘window-scale-body’ is ‘t’, it returns the largest integer
          smaller than WINDOW’s body pixel height divided by WINDOW’s
          character height.

        • If ‘window-scale-body’ is the symbol ‘spaced’, it returns the
          largest integer smaller than WINDOW’s body pixel height
          divided by WINDOW’s spaced character height.

     If PIXELWISE is non-‘nil’, the return value is always rounded down
     to the nearest integer, if necessary.  This means that if a line at
     the bottom of the text area is only partially visible, that line is
     not counted.  It also means that if ‘window-scale-body’ is ‘nil’,
     the value returned by this function can never exceed the value
     returned by ‘window-total-height’ for WINDOW.

martin