sink paramers not moved into closure (refc)

[arnetheduck]

Description

proc fff(v: sink string): iterator(): char =
  return iterator(): char =
    for c in v:
      yield c

var tmp = newString(100*1024*1024)

let iter = fff(move(tmp))

var i = 0
while true:
  let v = iter()
  if finished(iter):
    break

  i+=1
  discard

echo i
echo GC_getStatistics()

The above program should take no more than 100mb + some dust - ie the v parameter clearly can be moved into the iterator but isn't.

The copy happens during environment construction here:

 T1_ = NIM_NIL;  T1_ = (*colonenv_).v1; (*colonenv_).v1 = copyStringRC1(v);      if (T1_) nimGCunrefNoCycle(T1_);

Notably, this only affects refc - devel detects the sink parameter and moves the instance correctly.

This issue in particular can be seen with the {.async.} transformation for both std and chronos - solving it would cut memory usage in something like #13923 by half, most probably.

Nim Version

1.6.12, devel (refc)

Current Output

No response

Expected Output

No response

Possible Solution

No response

Additional Information

No response