Change deprecation mechanism to use a function

[nicoddemus]

As discussed in #7362 (comment)_, let's change our warnings mechanism to include a new PytestExpiredDeprecationWarning exception which is chosen at runtime depending on the current pytest version.

This will simplify our side because we won't need to change PytestDeprecationWarnings into errors anymore before each major release.

[nicoddemus]

Also, test_deprecation_warning_as_error will probably be removed.

[nicoddemus]

I'll be reverting these entries from the CHANGELOG:

- `#6981 <https://github.com/pytest-dev/pytest/issues/6981>`_: Deprecate the ``pytest.collect`` module as it's just aliases into ``pytest``.


- `#7097 <https://github.com/pytest-dev/pytest/issues/7097>`_: The ``pytest._fillfuncargs`` function is now deprecated. This function was kept
  for backward compatibility with an older plugin.

  It's functionality is not meant to be used directly, but if you must replace
  it, use `function._request._fillfixtures()` instead, though note this is not
  a public API and may break in the future.

EDIT: done in #7482

[nicoddemus]

@RonnyPfannschmidt I just realized something.

The plan here is to have a function somewhat like this:

def deprecated(reason: str, *, due: int, stacklevel: int):
    if due >= pytest version [0]:
        warnings.warn(PytestExpiredDeprecationWarning(reason), stacklevel=stacklevel)
    else:
        warnings.warn(PytestDeprecationWarning(reason), stacklevel=stacklevel)

Usage:

def use_of_deprecated_thing():
   deprecated("don't use this function, use X instead", due=7)
   # do its thing

However, because our version depends on the tag of the release, the actual pytest version will stay 6.X until the actual tag 7.0.0 is pushed at release time, and in that moment that function will issue PytestExpiredDeprecationWarning, which will then break the actual release. Any ideas?

[RonnyPfannschmidt]

For implementation towncrier support in setuptools_scm is intended and planned

[nicoddemus]

For implementation towncrier support in setuptools_scm is intended and planned

Not sure what you mean, can you elaborate please?

[graingert]

Remember the stacklevel for warnings.warn:

def deprecated(reason: str, *, due: int, stacklevel=0):
    stacklevel = stacklevel + 1
    if due >= pytest version [0]:
        warnings.warn(PytestExpiredDeprecationWarning(reason), stacklevel=stacklevel)
    else:
        warnings.warn(PytestDeprecationWarning(reason), stacklevel=stacklevel)

[RonnyPfannschmidt]

I strongly oppose combining declaration and triggering of warnings

[RonnyPfannschmidt]

@nicoddemus if the next guessed version is based on semver + towncrier inference, it's 7.0.dev... As soon as a breaking change is merged

[nicoddemus]

I strongly oppose combining declaration and triggering of warnings

Noted, just to get this out of the way then:

def deprecated_warning(reason: str, *, due: int) -> PytestWarning:
    if due >= pytest version [0]:
        return PytestExpiredDeprecationWarning(reason)
    else:
        return PytestDeprecationWarning(reason)

@nicoddemus if the next guessed version is based on semver + towncrier inference, it's 7.0.dev... As soon as a breaking change is merged

Ahh I see, thanks.

Should we hold this issue until that happens then?

[RonnyPfannschmidt]

Yup