Just to note: I consider this bug pretty important. The example function looks artificial, but I got the real failure by combining macros from different packages (`dash.el' for all the `it' bindings, plus `pcase' and `iter2' for lambdas, but I'm pretty sure you could get a failure with nested complicated `pcase' alone, if you want to go "only built-in" route). So, while it is apparently unlikely, you still can stumble into an incomprehensible breakdown in any sofisticated function by nesting enough macros that work otherwise and actually produce code that should work also in this case. But doesn't, when byte-compiled.

Paul

On Sat, 20 Nov 2021 at 05:44, Michael Heerdegen <michael_heerdegen@web.de> wrote:

Hello Paul,

thanks for the report, I can reproduce the issue, there is something
going wrong when compiling. I guess this is something for Mattias or
Stefan maybe? (CC'd)

#+begin_src emacs-lisp
; -*- lexical-binding: t -*-

(defun wtf (x)
(let ((it 0))
#'(lambda ()
(let ((fn #'(lambda () it)))
(if x
(let ((it x))
it)
(funcall fn))))))
#+end_src

Byte compile:

> wtf.el:9:17:Warning: reference to free variable ‘it’

(funcall (wtf 1))

> Symbol’s value as variable is void: it

while expected result is 1. Uncompiled code works as expected.

TIA,

Michael.