bug#54800: 28.1; calc: Cursor positioned at weird position in calc stack

[Christoph Arenz <tiga.arenz@web.de>]

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When the content of the calc stack inclusive top-of-stack symbol `.'
gets larger in height than the calc window, the cursor is positioned at
a weird position in the upper half of the stack window. When
line-numbering is on, the cursor is positioned at the beginning of the
line at the line number. Calling `calc-realign' does not change the
cursor postion.

How to reproduce:
1. emacs -Q
2. C-x * * (to start calc)
3. enter a number and RET
4. repeat No. 3 until the stacks grows and the symptom appears

Expected behavior for the cursor is to be placed on the `.' symbol,
representing the top of the stack.

5. After pressing `o' [calc-realign], the expected behavior would also
be for the cursor to be positioned at the top of the calc stack.

Debugging the function calc-align-stack-window with edebug, the symptom
goes away when placing a breakpoint at the line
(calc-cursor-stack-index 0) just after the set-window-start call, and
then continuing from there.

The following patch fixes the problem for me, but I do not fully
understand the NOFORCE option of the set-window-start function.

Thanks, Christoph

1 file changed, 1 insertion(+), 1 deletion(-)
lisp/calc/calc.el | 2 +-

modified   lisp/calc/calc.el
@@ -1816,7 +1816,7 @@ calc-align-stack-window
            (progn
          (calc-cursor-stack-index 0)
          (vertical-motion (- 2 (window-height win)))
-        (set-window-start win (point)))))
+        (set-window-start win (point) 'noforce))))
      (calc-cursor-stack-index 0)
      (if (looking-at " *\\.$")
          (goto-char (1- (match-end 0)))))


In GNU Emacs 28.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30,
cairo version 1.15.10)
of 2022-04-05 built on M92p
Repository revision: 5a223c7f2ef4c31abbd46367b6ea83cd19d30aa7
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.6 LTS

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
LCMS2 LIBOTF LIBSELINUX LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY PDUMPER
PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM
GTK3 ZLIB

Important settings:
value of $LC_MONETARY: de_DE.UTF-8
value of $LC_NUMERIC: de_DE.UTF-8
value of $LC_TIME: de_DE.UTF-8
value of $LANG: en_US.UTF-8
value of $XMODIFIERS: @im=ibus
locale-coding-system: utf-8-unix


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