Sphinx-autobuild fails on Python 3.8, on Windows

[Peilonrayz]

The source of the issue is better described on this tornado issue, in short 3.8 is making proactor the default asyncio event loop on Windows.

To Reproduce

• Load Windows
• Install Python 3.8

• $ pip list
  Sphinx                        2.4.4
  $ cd docs
  $ sphinx-autobulid
  Traceback (most recent call last):
    ...
    File "C:\Program Files\Python\3.8.0\Lib\asyncio\events.py", line 501, in add_reader 
      raise NotImplementedError
  NotImplementedError

I can provide more complete reproducible instructions if needed.

[tk0miya]

Could you paste a full traceback please? In addition, could you check that is the error raised also on using only sphinx-build?

[Peilonrayz]

This error is not raised in sphinx-build.

Full traceback

nox > sphinx-autobuild --open-browser -b html -W -d _build/doctrees . _build/html     

+--------- manually triggered build ---------------------------------------------
| Running Sphinx v2.4.4
| building [mo]: targets for 0 po files that are out of date
| building [html]: targets for 6 source files that are out of date
| updating environment: [new config] 6 added, 0 changed, 0 removed
f:\peilonrayz\nox\.nox\docs\lib\site-packages\recommonmark\parser.py:75: UserWarning: 
Container node skipped: type=document
  warn("Container node skipped: type={0}".format(mdnode.t))
| reading sources... [ 16%] CHANGELOG
| reading sources... [ 33%] CONTRIBUTING
| reading sources... [ 50%] config
| reading sources... [ 66%] index
| reading sources... [ 83%] tutorial
| reading sources... [100%] usage
| 
| looking for now-outdated files... none found
| pickling environment... done
| checking consistency... done
| preparing documents... done
| writing output... [ 16%] CHANGELOG
| writing output... [ 33%] CONTRIBUTING
| writing output... [ 50%] config
| writing output... [ 66%] index
| writing output... [ 83%] tutorial
| writing output... [100%] usage
| 

Warning, treated as error:
F:\Peilonrayz\nox\docs\index.rst:4:toctree contains reference to document 'CONTRIBUTING' that doesn't have a title: no link will be generated
+--------------------------------------------------------------------------------

[I 200315 02:30:42 server:296] Serving on http://127.0.0.1:8000
Traceback (most recent call last):
  File "c:\program files\python\3.8.0\lib\runpy.py", line 192, in _run_module_as_main 
    return _run_code(code, main_globals, None,
  File "c:\program files\python\3.8.0\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "F:\Peilonrayz\nox\.nox\docs\Scripts\sphinx-autobuild.EXE\__main__.py", line 7, in <module>
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\sphinx_autobuild\__init__.py", line 315, in main
    server.serve(port=portn, host=args.host,
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\livereload\server.py", line 298, in serve
    self.application(
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\livereload\server.py", line 253, in application
    app.listen(port, address=host)
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\tornado\web.py", line 2116, in listen
    server.listen(port, address)
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\tornado\tcpserver.py", line 152, in listen
    self.add_sockets(sockets)
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\tornado\tcpserver.py", line 165, in add_sockets
    self._handlers[sock.fileno()] = add_accept_handler(
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\tornado\netutil.py", line 279, in add_accept_handler
    io_loop.add_handler(sock, accept_handler, IOLoop.READ)
  File "f:\peilonrayz\nox\.nox\docs\lib\site-packages\tornado\platform\asyncio.py", line 100, in add_handler
    self.asyncio_loop.add_reader(fd, self._handle_events, fd, IOLoop.READ)
  File "c:\program files\python\3.8.0\lib\asyncio\events.py", line 501, in add_reader 
    raise NotImplementedError
NotImplementedError

[tk0miya]

It means this is a bug of sphinx-autobuild, right? This is an issue list for Sphinx core, not autobuild.
Please report this to their project.
Thanks,