Raise RTD doc build warnings as errors

[awaelchli]

What does this PR do?

Follow up to #1821 as discussed on slack

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[mergify]

This pull request is now in conflict... :(

[Borda]

RTD build - https://readthedocs.org/projects/pytorch-lightning/builds/11039117/

UPDATE: it seems to be freezing before beginning on Triggered state
ref: readthedocs/readthedocs.org#2257 readthedocs/readthedocs.org#435

[pep8speaks]

Hello @awaelchli! Thanks for updating this PR.

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2020-05-14 14:05:32 UTC

[codecov]

Codecov Report

Merging #1823 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1823   +/-   ##
======================================
  Coverage      88%     88%           
======================================
  Files          71      71           
  Lines        4458    4458           
======================================
  Hits         3915    3915           
  Misses        543     543           

[Borda]

@awaelchli seems to be failing https://readthedocs.org/projects/pytorch-lightning/builds/11039178/

The name of the builder is: epub/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/recommonmark/parser.py:65: UserWarning: Container node skipped: type=document
  warn("Container node skipped: type={0}".format(mdnode.t))

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/cmd/build.py", line 276, in build_main
    app.build(args.force_all, filenames)
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/application.py", line 349, in build
    self.builder.build_update()
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/builders/__init__.py", line 299, in build_update
    len(to_build))
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/builders/__init__.py", line 364, in build
    self.finish()
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/builders/html.py", line 638, in finish
    self.handle_finish()
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/builders/epub3.py", line 81, in handle_finish
    self.build_toc()
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/builders/_epub_base.py", line 705, in build_toc
    self.check_refnodes(refnodes)
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/builders/_epub_base.py", line 211, in check_refnodes
    logger.warning(__('duplicated ToC entry found: %s'), node['refuri'])
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 1736, in warning
    self.log(WARNING, msg, *args, **kwargs)
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/util/logging.py", line 124, in log
    super().log(level, msg, *args, **kwargs)
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 1768, in log
    self.logger.log(level, msg, *args, **kwargs)
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 1449, in log
    self._log(level, msg, args, **kwargs)
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 1519, in _log
    self.handle(record)
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 1529, in handle
    self.callHandlers(record)
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 1591, in callHandlers
    hdlr.handle(record)
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 901, in handle
    rv = self.filter(record)
  File "/home/docs/.pyenv/versions/3.7.3/lib/python3.7/logging/__init__.py", line 762, in filter
    result = f.filter(record)
  File "/home/docs/checkouts/readthedocs.org/user_builds/pytorch-lightning/envs/docs-rtd-warn-as-error/lib/python3.7/site-packages/sphinx/util/logging.py", line 406, in filter
    raise SphinxWarning(message)
sphinx.errors.SphinxWarning: duplicated ToC entry found: hooks.xhtml

Warning, treated as error:
duplicated ToC entry found: hooks.xhtml

maybe just disable whole epub build as we do not use it anyway...?

[Borda]

RTD build - https://readthedocs.org/projects/pytorch-lightning/builds/11039622/

[Borda]

RTD build - https://readthedocs.org/projects/pytorch-lightning/builds/11039662/

[awaelchli]

the build seems fine now, shall we remove the suppress warning now?

[Borda]

the build seems fine now, shall we remove the suppress warning now?

true :]