show dmypy errors post serving

[svalentin]

After dmypy starts serving, stdout and stderr gets captured. If we have an error, we assume we can send it to the client. However, if we have an error outside of client communication, that error is lost. The easiest way to see this is to run dmypy in daemonize mode, run a check once, then Control-C to send a KeyboardInterrupt. That exception is not printed though it should. After this change you can clearly see it.

term1$ python3 -m mypy.dmypy daemon

term2$ python3 -m mypy.dmypy check -v test.py
[... some output ...]

term1$ [Control-C]
^CTraceback (most recent call last):
  File "/home/svalentin/src/mypy-svalentin/mypy/dmypy_server.py", line 220, in serve
    with server:
  File "/home/svalentin/src/mypy-svalentin/mypy/ipc.py", line 232, in __enter__
    self.connection, _ = self.sock.accept()
  File "/usr/lib/python3.8/socket.py", line 292, in accept
    fd, addr = self._accept()
KeyboardInterrupt
Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/svalentin/src/mypy-svalentin/mypy/dmypy/__main__.py", line 6, in <module>
    console_entry()
  File "/home/svalentin/src/mypy-svalentin/mypy/dmypy/client.py", line 748, in console_entry
    main(sys.argv[1:])
  File "/home/svalentin/src/mypy-svalentin/mypy/dmypy/client.py", line 275, in main
    args.action(args)
  File "/home/svalentin/src/mypy-svalentin/mypy/dmypy/client.py", line 629, in do_daemon
    Server(options, args.status_file, timeout=args.timeout).serve()
  File "/home/svalentin/src/mypy-svalentin/mypy/dmypy_server.py", line 220, in serve
    with server:
  File "/home/svalentin/src/mypy-svalentin/mypy/ipc.py", line 232, in __enter__
    self.connection, _ = self.sock.accept()
  File "/usr/lib/python3.8/socket.py", line 292, in accept
    fd, addr = self._accept()
KeyboardInterrupt

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅