asyncio.start_server no error if you forget host and port

[Akuli]

It will error at runtime, but not when type checking.

(env) akuli@akuli-desktop:~/typeshed$ cat foo.py
import asyncio
asyncio.run(asyncio.start_server(print))

(env) akuli@akuli-desktop:~/typeshed$ mypy foo.py
Success: no issues found in 1 source file

(env) akuli@akuli-desktop:~/typeshed$ python3 foo.py
Traceback (most recent call last):
  File "/home/akuli/typeshed/foo.py", line 2, in <module>
    asyncio.run(asyncio.start_server(print))
  File "/usr/lib/python3.9/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
    return future.result()
  File "/usr/lib/python3.9/asyncio/streams.py", line 94, in start_server
    return await loop.create_server(factory, host, port, **kwds)
  File "/usr/lib/python3.9/asyncio/base_events.py", line 1504, in create_server
    raise ValueError('Neither host/port nor sock were specified')
ValueError: Neither host/port nor sock were specified

[Akuli]

I was going to make a PR that fixes this, but the error message was ridiculous, much worse than the error from runtime.

This can hardly be called an improvement. Also, the runtime error typically happens when you start your app, not in some rare corner case that only happens in production at 2AM.

So in short, this can't be fixed in a way that would be practically useful, at least not without something like python/typing#1043.