view CONTRIBUTING @ 51928:ad83e4f9b40e

typing: correct pytype mistakes in `mercurial/vfs.py`

With the previous changes in this series (prior to merging the *.pyi file), this
wasn't too bad- the only definitively wrong things were the `data` argument to
`writelines()`, and the return type on `backgroundclosing()` (both of these
errors were dropped in the previous commit; for some reason pytype doesn't like
`contextlib._GeneratorContextManager`, even though that's what it determined it
is):

    File "/mnt/c/Users/Matt/hg/mercurial/vfs.py", line 411, in abstractvfs:
         Bad return type 'contextlib._GeneratorContextManager' for generator function abstractvfs.backgroundclosing [bad-yield-annotation]
      Expected Generator, Iterable or Iterator

PyCharm thinks this is `Generator[backgroundfilecloser], Any, None]`, which can
be reduced to `Iterator[backgroundfilecloser]`, but pytype flagged the line that
calls `yield` without an argument unless it's also `Optional`.  PyCharm is happy
either way.  For some reason, `Iterable` didn't work for pytype:

    File "/mnt/c/Users/Matt/hg/mercurial/vfs.py", line 390, in abstractvfs:
        Function contextlib.contextmanager was called with the wrong arguments [wrong-arg-types]
             Expected: (func: Callable[[Any], Iterator])
      Actually passed: (func: Callable[[Any, Any, Any], Iterable[Optional[Any]]])
      Attributes of protocol Iterator[_T_co] are not implemented on Iterable[Optional[Any]]: __next__

Our full contribution guidelines are in our wiki, please see:

https://www.mercurial-scm.org/wiki/ContributingChanges

If you just want a checklist to follow, you can go straight to

https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist

If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).