Improve deprecation message for class-scoped fixtures as instance methods

[The-Compiler]

Shorten the message with -Werror slightly via __tracebackhide__, point out the name of the fixture, and fix some grammar issues.

Before:

Details

======================================================= ERRORS =======================================================
______________________________________ ERROR at setup of TestFixture.test_fixt _______________________________________

cls = <class '_pytest.runner.CallInfo'>, func = <function call_and_report.<locals>.<lambda> at 0x7f69abbe7cc0>
when = 'setup', reraise = (<class '_pytest.outcomes.Exit'>, <class 'KeyboardInterrupt'>)

    @classmethod
    def from_call(
        cls,
        func: Callable[[], TResult],
        when: Literal["collect", "setup", "call", "teardown"],
        reraise: type[BaseException] | tuple[type[BaseException], ...] | None = None,
    ) -> CallInfo[TResult]:
        """Call func, wrapping the result in a CallInfo.
    
        :param func:
            The function to call. Called without arguments.
        :type func: Callable[[], _pytest.runner.TResult]
        :param when:
            The phase in which the function is called.
        :param reraise:
            Exception or exceptions that shall propagate if raised by the
            function, instead of being wrapped in the CallInfo.
        """
        excinfo = None
        instant = timing.Instant()
        try:
>           result: TResult | None = func()
                                     ^^^^^^

src/_pytest/runner.py:361: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
src/_pytest/runner.py:250: in <lambda>
    lambda: runtest_hook(item=item, **kwds),
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/pluggy/_hooks.py:512: in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/pluggy/_manager.py:120: in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/logging.py:858: in pytest_runtest_setup
    yield
src/_pytest/capture.py:895: in pytest_runtest_setup
    return (yield)
            ^^^^^
src/_pytest/runner.py:170: in pytest_runtest_setup
    item.session._setupstate.setup(item)
src/_pytest/runner.py:536: in setup
    col.setup()
src/_pytest/python.py:1712: in setup
    self._request._fillfixtures()
src/_pytest/fixtures.py:807: in _fillfixtures
    item.funcargs[argname] = self.getfixturevalue(argname)
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/fixtures.py:631: in getfixturevalue
    fixturedef = self._get_active_fixturedef(argname)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/fixtures.py:727: in _get_active_fixturedef
    fixturedef.execute(request=subrequest)
src/_pytest/fixtures.py:1233: in execute
    result: FixtureValue = ihook.pytest_fixture_setup(
.venv/lib/python3.14/site-packages/pluggy/_hooks.py:512: in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/pluggy/_manager.py:120: in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/setuponly.py:36: in pytest_fixture_setup
    return (yield)
            ^^^^^
src/_pytest/fixtures.py:1314: in pytest_fixture_setup
    fixturefunc = resolve_fixture_function(fixturedef, request)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

fixturedef = <FixtureDef argname='fixt' scope='class' baseid='test_fixt.py::TestFixture'>
request = <SubRequest 'fixt' for <Function test_fixt>>

    def resolve_fixture_function(
        fixturedef: FixtureDef[FixtureValue], request: FixtureRequest
    ) -> _FixtureFunc[FixtureValue]:
        """Get the actual callable that can be called to obtain the fixture
        value."""
        fixturefunc = fixturedef.func
        # The fixture function needs to be bound to the actual
        # request.instance so that code working with "fixturedef" behaves
        # as expected.
        instance = request.instance
    
        if fixturedef._scope is Scope.Class:
            # Check if fixture is an instance method (bound to instance, not class)
            if hasattr(fixturefunc, "__self__"):
                bound_to = fixturefunc.__self__
                # classmethod: bound_to is the class itself (a type)
                # instance method: bound_to is an instance (not a type)
                if not isinstance(bound_to, type):
>                   warnings.warn(CLASS_FIXTURE_INSTANCE_METHOD, stacklevel=2)
E                   pytest.PytestRemovedIn10Warning: Class-scoped fixture defined as instance method is deprecated.
E                   Instance attributes set in this fixture will NOT be visible to test methods,
E                   as each test gets a new instance while the fixture runs only once per class.
E                   Use @classmethod decorator and set attributes on cls instead.
E                   See https://docs.pytest.org/en/stable/deprecations.html#class-scoped-fixture-as-instance-method

src/_pytest/fixtures.py:1290: PytestRemovedIn10Warning
============================================== short test summary info ===============================================
ERROR test_fixt.py::TestFixture::test_fixt - pytest.PytestRemovedIn10Warning: Class-scoped fixture defined as instance method is deprecated.

after:

Details

======================================================= ERRORS =======================================================
______________________________________ ERROR at setup of TestFixture.test_fixt _______________________________________

cls = <class '_pytest.runner.CallInfo'>, func = <function call_and_report.<locals>.<lambda> at 0x7fc8fd6235e0>
when = 'setup', reraise = (<class '_pytest.outcomes.Exit'>, <class 'KeyboardInterrupt'>)

    @classmethod
    def from_call(
        cls,
        func: Callable[[], TResult],
        when: Literal["collect", "setup", "call", "teardown"],
        reraise: type[BaseException] | tuple[type[BaseException], ...] | None = None,
    ) -> CallInfo[TResult]:
        """Call func, wrapping the result in a CallInfo.
    
        :param func:
            The function to call. Called without arguments.
        :type func: Callable[[], _pytest.runner.TResult]
        :param when:
            The phase in which the function is called.
        :param reraise:
            Exception or exceptions that shall propagate if raised by the
            function, instead of being wrapped in the CallInfo.
        """
        excinfo = None
        instant = timing.Instant()
        try:
>           result: TResult | None = func()
                                     ^^^^^^

src/_pytest/runner.py:361: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
src/_pytest/runner.py:250: in <lambda>
    lambda: runtest_hook(item=item, **kwds),
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/pluggy/_hooks.py:512: in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/pluggy/_manager.py:120: in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/logging.py:858: in pytest_runtest_setup
    yield
src/_pytest/capture.py:895: in pytest_runtest_setup
    return (yield)
            ^^^^^
src/_pytest/runner.py:170: in pytest_runtest_setup
    item.session._setupstate.setup(item)
src/_pytest/runner.py:536: in setup
    col.setup()
src/_pytest/python.py:1712: in setup
    self._request._fillfixtures()
src/_pytest/fixtures.py:808: in _fillfixtures
    item.funcargs[argname] = self.getfixturevalue(argname)
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/fixtures.py:632: in getfixturevalue
    fixturedef = self._get_active_fixturedef(argname)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/fixtures.py:728: in _get_active_fixturedef
    fixturedef.execute(request=subrequest)
src/_pytest/fixtures.py:1234: in execute
    result: FixtureValue = ihook.pytest_fixture_setup(
.venv/lib/python3.14/site-packages/pluggy/_hooks.py:512: in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/pluggy/_manager.py:120: in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/_pytest/setuponly.py:36: in pytest_fixture_setup
    return (yield)
            ^^^^^
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

fixturedef = <FixtureDef argname='fixt' scope='class' baseid='test_fixt.py::TestFixture'>
request = <SubRequest 'fixt' for <Function test_fixt>>

    def pytest_fixture_setup(
        fixturedef: FixtureDef[FixtureValue], request: SubRequest
    ) -> FixtureValue:
        """Execution of fixture setup."""
        kwargs = {}
        for argname in fixturedef.argnames:
            kwargs[argname] = request.getfixturevalue(argname)
    
>       fixturefunc = resolve_fixture_function(fixturedef, request)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E       pytest.PytestRemovedIn10Warning: Class-scoped fixtures defined as instance methods are deprecated.
E       Instance attributes set in the 'fixt' fixture will NOT be visible to test methods,
E       as each test gets a new instance while the fixture runs only once per class.
E       Use a @classmethod decorator below @pytest.fixture and set attributes on cls instead.
E       See https://docs.pytest.org/en/stable/deprecations.html#class-scoped-fixture-as-instance-method

src/_pytest/fixtures.py:1323: PytestRemovedIn10Warning
============================================== short test summary info ===============================================
ERROR test_fixt.py::TestFixture::test_fixt - pytest.PytestRemovedIn10Warning: Class-scoped fixtures defined as instance methods are deprecated.
================================================== 1 error in 0.17s =================================================

Still definitely not optimal, but I can't think of a way to further improve this easily.

[nicoddemus]

Still definitely not optimal, but I can't think of a way to further improve this easily.

Indeed.

Once we turn this into an error, we can then raise UsageError, which will show no traceback at all.

[The-Compiler]

don't think this needs a changelog, opinions?

[nicoddemus]

don't think this needs a changelog, opinions?

Agreed