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

[martin rudalics <rudalics@gmx.at>]

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 >>> 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).

I think MAX-WIDTH should be nil here.

 >>> 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.

This would not work.  The 'height' frame parameter counts in characters
while 'window-text-pixel-size' wants pixels as X-LIMIT.  Also, the sizes
of frame and window decorations would hardly match.

 >>> 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.

Please try the attached diff.

Thanks, martin

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diff --git a/lisp/window.el b/lisp/window.el
index 1b8fe2b262..7b8ca87f6a 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -9382,14 +9382,17 @@ fit-frame-to-buffer-1
              ((numberp (nth 1 sizes)) (* (nth 1 sizes) line-height))
              (t (window-min-size window nil nil t))))
            (max-width
-            (min
-             (cond
-              ((numberp max-width) (* max-width char-width))
-              ((numberp (nth 2 sizes)) (* (nth 2 sizes) char-width))
-              (t parent-or-display-width))
-             ;; The following is the maximum width that fits into the
-             ;; left and right margins.
-             (max (- right-margin left-margin outer-minus-body-width))))
+            (let ((max-width
+                   (cond
+                    ((numberp max-width) (* max-width char-width))
+                    ((numberp (nth 2 sizes)) (* (nth 2 sizes) char-width))
+                    ((not (eq only 'vertically)) parent-or-display-width))))
+              (when (numberp max-width)
+                (min max-width
+                     ;; The following is the maximum width that fits
+                     ;; into the left and right margins.
+                     (max (- right-margin left-margin
+                             outer-minus-body-width))))))
            (min-width
             (cond
              ((numberp min-width) (* min-width char-width))