"Error: invalid type: 'void' for var" compile error on AsyncHttpClient.downloadFile (devel branch)

[rominf]

Nim from the devel branch doesn't compile simple example with AsyncHttpClient.downloadFile.

Example

import asyncdispatch
import httpclient

proc test_async {.async.} =
  var client = newAsyncHttpClient()
  await client.downloadFile("http://speedtest-ams2.digitalocean.com/10mb.test", "/tmp/10mb.test")
  
waitFor test_async()

Current Output

Hint: used config file '/home/rominf/dev/nim/config/nim.cfg' [Conf]
Hint: used config file '/home/rominf/dev/nim/config/config.nims' [Conf]
................................................
/tmp/test_asynchttpclient_downloadfile_bug.nim(4, 19) template/generic instantiation of `async` from here
/tmp/test_asynchttpclient_downloadfile_bug.nim(6, 15) template/generic instantiation of `downloadFile` from here
/home/rominf/dev/nim/lib/pure/httpclient.nim(1250, 28) template/generic instantiation of `downloadFileEx` from here
/home/rominf/dev/nim/lib/pure/httpclient.nim(1226, 3) Error: invalid type: 'void' for var

Expected Output

[downloaded file]

Possible Solution

If I change httpclient implementation:

-proc downloadFile*(client: AsyncHttpClient, url: Uri | string,
+proc downloadFile*(client: AsyncHttpClient, url: string,

it works again.

$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-01-17
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 6c07b0a1f8daf96078ae68b83ead1d48675969d7
active boot switches: -d:release

[ghost]

Seems to be caused by #15919 - on line 1226 there's a generic proc inside of another generic proc, so the compiler doesn't like that (or maybe it's not allowed at all).

One possible solution is to move downloadFileEx out of downloadFile, then it starts working again.

[timotheecour]

on line 1226 there's a generic proc inside of another generic proc, so the compiler doesn't like that (or maybe it's not allowed at all).

wrong diagnostic, generic inside generic is ok. I just filed #16786 which shows root cause