Async causes return, which is only run if nothing raises, to be considered as as always run.

[kayabaNerve]

If a raisable statement and a return is inside a try/catch, any code after the raises will be considered unreachable, despite the fact that if the raisable statement raises the return is not executed.

Example

import asyncdispatch

proc trySync() {.async.} =
  raise newException(ValueError, "")

proc x() {.async.} =
  try:
    await trySync()
    return
  except ValueError:
    discard
  
  echo "Hello"

Current Output

/usercode/in.nim(3, 18) template/generic instantiation of `async` from here
/usercode/in.nim(4, 3) Error: unreachable statement after 'return' statement or '{.noReturn.}' proc

Expected Output

Hello

Additional Information

Tested on Nim Playground 1.0.2.

[disruptek]

Whenever you have a situation like this, it's worked-around by providing a trailing block that the async can gobble up:

proc foo() {.async.} =
  block:
    raise newException(Exception, "")