Nim: SIGSEGV with iterator

[timotheecour]

# D20181006T142957
when defined(case1):
  # SIGSEGV
  import os
  proc foo(): auto =
    result = iterator (): auto =
      for path in walkPattern("*"):
        yield 0

when defined(case2):
  # ok
  import os
  iterator foo2(): auto =
    for path in walkPattern("*"):
      yield 0

when defined(case3):
  # SIGSEGV
  # reduced from os.walkPattern. any change seems to remove SIGSEGV
  iterator walkPattern2*(): int =
    defer:
      var ret: int
      let ret2 = addr(ret)
    yield 1

  proc foo(): auto =
    result = iterator (): auto =
      for ai in walkPattern2():
        yield 0

[LemonBoy]

Workaround: don't use auto
Life pro-tip: don't use auto

[timotheecour]

there are cases where explicit types is better (eg fwd declaration) but when type is complex, auto is more DRY

[krux02]

just tested it, not reproducable anymore.

[timotheecour]

indeed, doesn't crash anymore; just tested it, any use of the iterators produced by foo() will result CT error:
Error: expression 'temp()' has no type (or is ambiguous)

when true # was: defined(case3):
  # SIGSEGV
  # reduced from os.walkPattern. any change seems to remove SIGSEGV
  iterator walkPattern2*(): int =
    defer:
      var ret: int
      let ret2 = addr(ret)
    yield 1

  proc foo(): auto =
    result = iterator (): auto =
      for ai in walkPattern2():
        yield 0
    let temp = foo()
    for ai in temp():
      echo ai

but that's just a duplicate of https://github.com/nim-lang/Nim/issues/8284 so closing this was good