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

[Christoph Arenz]

On 09.04.22 09:34, Eli Zaretskii wrote:
> > Date: Fri, 8 Apr 2022 21:44:38 +0200
> > From: Christoph Arenz <tiga.arenz@web.de>
> >
> > 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, but I think using NOFORCE is not the best solution here,
> because that causes Emacs to recenter the stack window, thus showing
> fewer stack entries than possible.
>
> I think the bug is actually off-by-one error, because the
> vertical-motion call doesn't take the header-line into account.  So I
> suggest the following patch instead, please see if it solves the
> problem:

Your patch solves the problem and shows maximum content of the stack
in the window.
Note that it still contains the NOFORCE while the off-by-one fix also
works without it.

> diff --git a/lisp/calc/calc.el b/lisp/calc/calc.el
> index 81677d7..900940d 100644
> --- a/lisp/calc/calc.el
> +++ b/lisp/calc/calc.el
> @@ -1815,8 +1815,8 @@ calc-align-stack-window
>           (if win
>               (progn
>                 (calc-cursor-stack-index 0)
> -               (vertical-motion (- 2 (window-height win)))
> -               (set-window-start win (point)))))
> +               (vertical-motion (- 3 (window-height win)))
> +               (set-window-start win (point) 'noforce))))
>         (calc-cursor-stack-index 0)
>         (if (looking-at " *\\.$")
>             (goto-char (1- (match-end 0)))))