bug#36566: 27.0.50; debug is sometimes horribly slow

[Gemini Lasswell <gazally@runbox.com>]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> A case to reproduce the problem that doesn't require org files would be
> nice.  `data' in the example here is a parse tree, so perhaps the
> slowness is in printing tree-like structures?  (But I haven't actually
> tried to debug this.)

The slowness does come from printing large tree-like structures. Here is
a small example to reproduce the problem.  Paste the following code into
*scratch*:

(defun my-make-a-tree (depth)
  (if (natnump depth)
      (list (my-make-a-tree (1- depth)) (my-make-a-tree (1- depth)))
    (list 'leaf)))

(defun my-func ()
  (let ((tree (my-make-a-tree 13)))
    tree))

(my-func)

Evaluate the first form using C-M-x and the second using C-u C-M-x.
Then evaluate the third form with C-M-x.  You will enter Edebug; press
space to step through.

Result: Each step takes a few seconds and creates a message of about
150K characters.