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

From: Phillip Lord <[email-masked]>
Date: Fri, 01 May 2020 09:26:44 +0100

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.

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.