Treat warnings as errors

[tomchristie]

Closes #1686
Closes #1670

• Use -Werror when running pytest, to treat warnings as errors.
• Use try..finally around auth_flow generator usage, with a .close() in the finally block.
• Use getattr in __del__ to handle a case where an attribute might not exist on a partially initialised instance.
• Use a context managed open() file in a test case.
• Use ssl.PROTOCOL_TLS_CLIENT instead of deprecated ssl.PROTOCOL_TLS
• Use context.minimum_version = instead of context.options |= ssl.OP_NO_* on Python 3.10+

[tomchristie]

Weirdly, at this point the 3.10 test runs are hanging, but there's not any feedback to guide where or why.

[j178]

Ran tests locally, I find that it is because the uvicorn server failed to start if we treat warnings as error:

We need to get uvicorn running under 3.10 without warnings first.

Related: encode/uvicorn#1070

[tomchristie]

@j178 Fantastic bit of digging, thanks! Okay, so blocked on a 3.10 compatriot uvicorn release. Gotcha.

[graingert]

use filterwarnings=error

[j178]

This reminds me that we can use

filterwarnings = 
    error
    default:::uvicorn

to exempt uvicorn warnings, so that we will not be blocked by uvicorn.

[tomchristie]

use filterwarnings=error

Could you expand on that @graingert?

to exempt uvicorn warnings, so that we will not be blocked by uvicorn.

Oh, that's a great tip, @j178. I'm not sure what I need to do to inline that here, but will look into it.

[tomchristie]

Ah okay, cribbing an example from here pytest-dev/pytest#4180

[tool:pytest]
addopts =
  -W error
  -v
filterwarnings =
  error
  # ignored by default
  ignore::ImportWarning
  ignore::PendingDeprecationWarning
  # raised by Cython, usually harmless
  ignore:numpy.dtype size changed:RuntimeWarning
  ignore:numpy.ufunc size changed:RuntimeWarning
  # raised by Werkzeug
  ignore:Request.is_xhr is deprecated:DeprecationWarning
  # raised by Moto
  ignore:Flags not at the start of the expression:DeprecationWarning

[graingert]

The filterwarnings in option is preferred eg https://github.com/pytest-dev/pytest/blob/main/pyproject.toml#L23

[tomchristie]

to exempt uvicorn warnings, so that we will not be blocked by uvicorn.

Okay, gave that a try. Looks like 3.10 is still stuck.

[j178]

@tomchristie drop -Werror from addopts will work

[tomchristie]

Alrighty, ready for review I think.