test.nim:
#import parsecfg
import asynchttpserver, asyncdispatch
var server = newAsyncHttpServer()
proc cb(req: Request) {.async.} =
  await req.respond(Http200, "Hello World")

waitFor server.serve(Port(8080), cb)
------- parsecfg commented out ---------
$ nim --hints:off c test.nim
...
$
-------- parsecfg uncommented -------
$ nim --hints:off c test.nim
lib/pure/httpcore.nim(84, 20) Error: undeclared field: 'key'
$