bug#28915: Emacs 27 under macOS window system; improper frame resizing (off by 4 pixels)

[martin rudalics <rudalics@gmx.at>]

 > Each time the following two expressions are called, they increase the
 > width or height respectively of the selected frame by 4 pixels rather
 > than leaving the dimension unchanged.  Even if this is a rounding error
 > due to use of column/line math, shouldn't there be a special case test
 > for this that prevents the size change?  It would simplify coding.
 >
 > (progn (set-frame-width nil (frame-pixel-width) nil t)
 >         (frame-pixel-width))
 >
 > (progn (set-frame-height nil (frame-pixel-height) nil t)
 >         (frame-pixel-height))

This is not a bug.  For historic reasons, the second arguments of
‘set-frame-width’ and ‘set-frame-height’ must specify the width and
height of the _text area_ of the frame and not its native width and
height.  You can rely on this to never ever change.  Section 29.3.4
Frame Size of the Elisp manual should explain everything.

martin