bug#63586: 29.x: dotimes (possible) problem

[Eli Zaretskii]

> From: balducci@units.it
> Date: Fri, 19 May 2023 17:10:44 +0200
> 
> the dotimes macro behaves differently in 29.x with respect to previous
> versions
> 
> Basically: changing the value of the loop variable in the body of
> dotimes does not seem to have any effect, where for versions <29.x it
> used to.
> 
> Here is a minimal stretch of dummy code clarifying the problem I'm
> reporting.
> 
> emacs-29.0.91 (or 29.0.90)
> ==========================
> 
> (dotimes (ii 10)
> (insert (format "%2d " ii))
> (when (= ii 4)(setq ii 11))
> )
> ==>  0  1  2  3  4  5  6  7  8  9 
> 
> emacs-28.2 (or any version <29.x)
> =================================
> 
> (dotimes (ii 10)
> (insert (format "%2d " ii))
> (when (= ii 4)(setq ii 11))
> )
> ==>  0  1  2  3  4 

I can only reproduce the behavior you see in 28.2 in Emacs 26.3.  All
the later versions, starting from 27.1, behave like Emacs 29 does.

> The ability to jump out of the loop by pushing the loop variable over
> the upper limit is something that I happen to use in my scripts, so
> 29.x breaks them somehow
> 
> Of course, there are very many other equivalent ways to
> accomplish the same result, but I don't see why this one
> shouldn't be supported (any longer)
> 
> Is the changed behavior intentional? Am I missing some blatant point here?
> 
> AFAICS, changing the value of the loop variable from inside the loop
> body is supported by any other language which I know about

Adding Stefan and Mattias who made changes in dotimes recently.