bug#36566: 27.0.50; debug is sometimes horribly slow

[Gemini Lasswell <gazally@runbox.com>]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> BTW, when I eval this
>
> (let ((x '#1=(1 . #1#)))
>   (debug)
>   (cons x x))
>
> I get a backtrace like
>
> Debugger entered: nil
>   (let ((x '(1 . #6))) (debug) (cons x x))
>   eval((let ((x '(1 . #7))) (debug) (cons x x)) t)
>
> whereby when I hit C-u # all references get number 1, or start from 1
> for every frame:
>
> Debugger entered: nil
>   (let ((x '#1=(1 . #1#))) (debug) (cons x x))
>   eval((let ((x '#1=(1 . #1#))) (debug) (cons x x)) t)
>
> Just a minor inconvenience, though.

Without print-circle turned on, no hash table gets built to identify
objects, so the #<number> is only an indicator that a loop was found in
the data structure, not an indicator of any particular object. The
number printed comes from the depth of nested data structures at the
point the loop is detected.