Tuple destructuring is broken with closure iterators

[a-mr]

Compiler crashes with --gc:orc or has an internal error:

Example

iterator walk(): (int, int) {.closure.} =
  yield (10,11)

for (i,j) in walk():
  echo i

Current Output

nim c --gc:orc myng7.nim
Hint: used config file '/home/amakarov/activity-public/Nim/config/nim.cfg' [Conf]
Hint: used config file '/home/amakarov/activity-public/Nim/config/config.nims' [Conf]
Hint: used config file '/home/amakarov/activity-personal/nim-try/nim.cfg' [Conf]
....SIGSEGV: Illegal storage access. (Attempt to read from nil?)

Expected Output

not to crash

Possible Solution

Additional Information

$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2020-11-09
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: 53eca459f1d96c710238be95bd3fb048b336f2f3
active boot switches: -d:release

Possibly related with #15896.

[cooldome]

I had a look it is not arc related. Closure iterators and tuple unpacking don't play together in any gc mode

[a-mr]

It may be something very simple. When I rewrite it trivially without destructuring in the header of for, it works fine:

for x in walk():
  let (a, b) = x
  echo a, b, x

[ringabout]

iterator walk(): (int, int) {.closure.} =
  yield (10,11)

for i,j in walk():
  echo i

This works.