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>]

[-- Attachment #1: Type: text/plain, Size: 330 bytes --]

 >> I don't know yet either.  I'll send you a patch as soon as I have one.
 >
 > Sounds good, thanks.

I suppose we can manage by fixing some trivial silliness in the code and
making the documentation tell what the code does.  If you don't see any
problems with the attached diff within a week or so, I'll push it.

Thanks, martin

[-- Attachment #2: fit-frame-to-buffer.diff --]
[-- Type: text/x-patch, Size: 5274 bytes --]

diff --git a/doc/lispref/windows.texi b/doc/lispref/windows.texi
index e070e84c67..6a6c91e356 100644
--- a/doc/lispref/windows.texi
+++ b/doc/lispref/windows.texi
@@ -1151,10 +1151,12 @@ Resizing Windows
 its buffer exactly.  @var{frame} can be any live frame and defaults to
 the selected one.  Fitting is done only if @var{frame}'s root window is
 live.  The arguments @var{max-height}, @var{min-height}, @var{max-width}
-and @var{min-width} specify bounds on the new total size of
-@var{frame}'s root window.  @var{min-height} and @var{min-width} default
-to the values of @code{window-min-height} and @code{window-min-width}
-respectively.
+and @var{min-width}, if non-@code{nil}, specify bounds on the new body
+size of @var{frame}'s root window.  @var{min-height} and @var{min-width}
+default to the values of @code{window-safe-min-height} and
+@code{window-safe-min-width} respectively.  A non-@code{nil} value
+specified by any of these arguments overrides the corresponding value
+specified by @code{fit-frame-to-buffer-sizes}.
 
 If the optional argument @var{only} is @code{vertically}, this function
 may resize the frame vertically only.  If @var{only} is
@@ -1179,10 +1181,10 @@ Resizing Windows
 
 @defopt fit-frame-to-buffer-sizes
 This option specifies size boundaries for @code{fit-frame-to-buffer}.
-It specifies the total maximum and minimum lines and maximum and minimum
-columns of the root window of any frame that shall be fit to its buffer.
-If any of these values is non-@code{nil}, it overrides the corresponding
-argument of @code{fit-frame-to-buffer}.
+It specifies the maximum and minimum lines and maximum and minimum
+columns of the root window's body of any frame that shall be fit to its
+buffer.  Any value this option specifies will be overridden by the
+corresponding argument of @code{fit-frame-to-buffer}, if non-@code{nil}.
 @end defopt
 
 @deffn Command shrink-window-if-larger-than-buffer &optional window
diff --git a/lisp/window.el b/lisp/window.el
index a47a1216d1..cb59adc428 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -9053,10 +9053,11 @@ fit-frame-to-buffer-margins
 
 (defcustom fit-frame-to-buffer-sizes '(nil nil nil nil)
   "Size boundaries of frame for `fit-frame-to-buffer'.
-This list specifies the total maximum and minimum lines and
-maximum and minimum columns of the root window of any frame that
-shall be fit to its buffer.  If any of these values is non-nil,
-it overrides the corresponding argument of `fit-frame-to-buffer'.
+This list specifies the total maximum and minimum numbers of
+lines and the maximum and minimum numbers of columns of the body
+of the root window of any frame that shall be fit to its buffer.
+Any value specified by ths variable will be overridden by the
+corresponding argument of `fit-frame-to-buffer', if non-nil.
 
 On window systems where the menubar can wrap, fitting a frame to
 its buffer may swallow the last line(s).  Specifying an
@@ -9252,30 +9253,30 @@ fit-frame-to-buffer-1
               (t parent-or-display-height))
              ;; The following is the maximum height that fits into the
              ;; top and bottom margins.
-             (max (- bottom-margin top-margin outer-minus-body-height))))
+             (max (- bottom-margin top-margin outer-minus-body-height) 0)))
            (min-height
             (cond
              ((numberp min-height) (* min-height line-height))
              ((numberp (nth 1 sizes)) (* (nth 1 sizes) line-height))
-             (t (window-min-size window nil nil t))))
+             (t (window-safe-min-size window 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))))
+            (unless (eq only 'vertically)
+              (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) 0))))
            (min-width
             (cond
              ((numberp min-width) (* min-width char-width))
-             ((numberp (nth 3 sizes)) (nth 3 sizes))
-             (t (window-min-size window t nil t))))
+             ((numberp (nth 3 sizes)) (* (nth 3 sizes) char-width))
+             (t (window-safe-min-size window t t))))
            ;; Note: Currently, for a new frame the sizes of the header
            ;; and mode line may be estimated incorrectly
-           (size
-            (window-text-pixel-size window from to max-width max-height))
+           (size (window-text-pixel-size window from to max-width max-height))
            (width (max (car size) min-width))
            (height (max (cdr size) min-height)))
       ;; Don't change height or width when the window's size is fixed