Subject: bug#40992: 27.0.90; Evaluating a function while using edebug breaks

From: Alan Mackenzie <[email-masked]>
Date: Fri, 1 May 2020 15:56:30 +0000

Hello, Phillip and Lars.

On Fri, May 01, 2020 at 09:26:44 +0100, Phillip Lord wrote:

> Edebug fails while tracing a function, if that function is evaluated
> during the edebug session. The error reported is:

> Wrong type argument: listp, #<marker at 4045 in hanoi.el>
> edebug--display-1: Wrong type argument: listp, #<marker at 4045 in hanoi.el>

> This is a regression as it works in Emacs-26, but fails in Emacs-27.

Yes.  A bit of bisection shows that the commit which introduced this bug
is:
commit e8b3a15cb6ff187ce08afcb43bd9a0b7907268ca
Author: Lars Ingebrigtsen <[email-masked]>
Date:   Sun Oct 20 12:07:42 2019 +0200

    Mark breakpoints in edebug with highlights

    * lisp/emacs-lisp/edebug.el (edebug--overlay-breakpoints)
    (edebug--overlay-breakpoints-remove): New functions (bug#23468).
    (edebug-modify-breakpoint): Use them to highlight breakpoints.
    (edebug--display-1): Restore breakpoint highlights.
    (edebug--recursive-edit): Remove highlights on exit.

Lars, have you got any comment on this?

> Reproduction:

> In clean emacs -q

> M-x hanoi
> jump to hanoi function
> C-u C-M-x
> M-x hanoi

> After stepping through into hanoi with point still in

> C-M-x

> and step once more.

> I use this workflow quite a lot when debugging. I may start to debug a
> function, decided I have seen enough, to un-instrument so I don't see it
> debugged again.

-- 
Alan Mackenzie (Nuremberg, Germany).