I now came up with a fix for 'fit-window-to-buffer' too which had some
strange misbehavior with different size restricting arguments when the
window's text size did not change.  See attached diffs and Change Log
below.

 > I think I understand better now, I was hampered by some weird debugging
 > artifacts in my current setup.  With the default
 > `frame-resize-pixelwise' of nil, and the otherwise bug-fixed code,
 > nothing is cut off, but there is some slack whitespace, indeed.

I suppose that part of that whitespace comes from the fact that with
'line-spacing' greater zero, 'window-text-pixel-size' includes the
space below the last line of its text.  It would be nice to get rid of
that but ISTR that a line's text may now get centered within the space
reserved for it.  So I cannot just remove the entire line space of one
line from the return value but probably only half of the line spacing
value.  How would I know the right value?

martin


Fixes for fitting windows and frames to their buffers (Bug#37563)

* lisp/window.el (window-default-font-height)
(window-default-line-height): New functions.
(fit-frame-to-buffer): Interpret values of MAX-HEIGHT and
MIN-HEIGHT arguments in terms of WINDOW's default line height
(Bug#37563).
(fit-window-to-buffer): Obey size restricting arguments even
when size of WINDOW's text does not change.  Do not
temporarily select WINDOW and perform height/width related
calculations if and only if WINDOW is accordingly combined.
Interpret values of MAX-HEIGHT and MIN-HEIGHT arguments in
terms of WINDOW's default line height.