internal error for auto iterator

[pb-cdunn]

EDIT by @narimiran - simplified example at the top, so our tools can pick it up:

iterator FaiReader(): string {.closure.} =
  yield "something"

template toClosure(i): auto =
  iterator j: string {.closure.} =
    for x in FaiReader():
      yield x
  j

proc main = 
  var reader = toClosure(FaiReader())

main()

---

Somewhat related: #5859

I am trying to pass an iterator to another proc. To do that, I've tried using the toClosure() template from @def- : https://forum.nim-lang.org/t/2027

Example

https://github.com/bio-nim/pb/blob/internal-error/src/falconcpkg/rotate.nim

(Hopefully that file will compile for you if you copy/paste, as I've commented out the dependencies.)

Current Output

rotate.nim(182, 9) Error: internal error: expr: var not init FaiReader_932476
No stack traceback available

180 template toClosure(i): auto =
181   iterator j: type(i) {.closure.} =
182     for x in i:
183       yield x
184   j
...
199     var reader = toClosure(FaiReader(fin, full_sequence))

Expected Output

I am willing to do this a different way. I just can't figure out how to pass an "iterator" to another proc, the way I would pass a "generator" in Python.

I thought toClosure() would at least allow me to see the type it returns, using typetraits, but I cannot get this to compile at all.

Possible Solution

No idea. For now, I will simply avoid passing an iterator. But it's a useful pattern if it can work. Again, here is info on passing iterators: https://forum.nim-lang.org/t/2027

Additional Information

$ nim -v
Nim Compiler Version 1.0.99 [Linux: amd64]
Compiled at 2019-09-28

also fails for

Nim Compiler Version 0.20.2 [Linux: amd64]
Compiled at 2019-07-17

I'm on Linux.

[pb-cdunn]

Some discussion at https://forum.nim-lang.org/t/5384

This might be a subtle compiler bug.

[ghost]

Short example to reproduce:

iterator FaiReader(): string {.closure.} =
  yield "something"

template toClosure(i): auto =
  iterator j: string {.closure.} =
    for x in FaiReader():
      yield x
  j

proc main = 
  var reader = toClosure(FaiReader())

main()

[metagn]

Works in devel but not in 2.0?

[metagn]

Fails again since #24108 and works with -d:nimOptIter, meaning #23787 fixed it