GNU bug report logs - #28725
26.0.60; Error when using Edebug on a generator

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From: Gemini Lasswell <gazally <at> runbox.com>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 28725 <at> debbugs.gnu.org
Subject: bug#28725: 26.0.60; Error when using Edebug on a generator
Date: Mon, 21 Oct 2019 09:29:04 -0700

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> I'm able to reproduce this bug in Emacs 27.
>
> Does anybody know what's causing this?  It's bugging out in the
> `iter-yield' call.

I took a look and I think the problem is that cps--transform-1 doesn't
look inside lambda forms.  When Edebug instruments a function, it wraps
the body of the function in a lambda form.

Here's a code sample to reproduce the bug with just eval-buffer, no
Edebug necessary:

;;;  -*- lexical-binding: t -*-

(require 'generator)

(iter-defun mycounter (start)
  (let ((i 0)
	(offset-yield-func (lambda (x) (iter-yield (+ x start)))))
    (while t
      (funcall offset-yield-func i)
      (setq i (1+ i)))))

(defun my-iter-do ()
  (let (results
	(tally (mycounter 10)))
    (dotimes (_ 4)
      (push (iter-next tally) results))
    results))

(my-iter-do)

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