Mark some public and to-be-public classes as @final

changelog/7780.improvement.rst

@@ -0,0 +1,3 @@
+Public classes which are not designed to be inherited from are now marked `@final <https://docs.python.org/3/library/typing.html#typing.final>`_.
+Code which inherits from these classes will trigger a type-checking (e.g. mypy) error, but will still work in runtime.
+Currently the ``final`` designation does not appear in the API Reference but hopefully will in the future.

src/_pytest/_code/code.py

@@ -38,6 +38,7 @@
 from _pytest._io.saferepr import safeformat
 from _pytest._io.saferepr import saferepr
 from _pytest.compat import ATTRS_EQ_FIELD
+from _pytest.compat import final
 from _pytest.compat import get_real_func
 from _pytest.compat import overload
 from _pytest.compat import TYPE_CHECKING
@@ -414,6 +415,7 @@ def recursionindex(self) -> Optional[int]:
 _E = TypeVar("_E", bound=BaseException, covariant=True)
 
 
+@final
 @attr.s(repr=False)
 class ExceptionInfo(Generic[_E]):
     """Wraps sys.exc_info() objects and offers help for navigating the traceback."""

src/_pytest/_io/terminalwriter.py

@@ -7,6 +7,7 @@
 from typing import TextIO
 
 from .wcwidth import wcswidth
+from _pytest.compat import final
 
 
 # This code was initially copied from py 1.8.1, file _io/terminalwriter.py.
@@ -36,6 +37,7 @@ def should_do_markup(file: TextIO) -> bool:
     )
 
 
+@final
 class TerminalWriter:
     _esctable = dict(
         black=30,

src/_pytest/cacheprovider.py

@@ -21,6 +21,7 @@
 from .reports import CollectReport
 from _pytest import nodes
 from _pytest._io import TerminalWriter
+from _pytest.compat import final
 from _pytest.compat import order_preserving_dict
 from _pytest.config import Config
 from _pytest.config import ExitCode
@@ -50,6 +51,7 @@
 """
 
 
+@final
 @attr.s
 class Cache:
     _cachedir = attr.ib(type=Path, repr=False)

src/_pytest/capture.py

@@ -17,6 +17,7 @@
 from typing import Union
 
 import pytest
+from _pytest.compat import final
 from _pytest.compat import TYPE_CHECKING
 from _pytest.config import Config
 from _pytest.config.argparsing import Parser
@@ -498,6 +499,7 @@ def writeorg(self, data):
 # pertinent parts of a namedtuple. If the mypy limitation is ever lifted, can
 # make it a namedtuple again.
 # [0]: https://github.com/python/mypy/issues/685
+@final
 @functools.total_ordering
 class CaptureResult(Generic[AnyStr]):
     """The result of :method:`CaptureFixture.readouterr`."""

src/_pytest/compat.py

@@ -19,7 +19,6 @@
 
 import attr
 
-from _pytest._io.saferepr import saferepr
 from _pytest.outcomes import fail
 from _pytest.outcomes import TEST_OUTCOME
 
@@ -297,6 +296,8 @@ def get_real_func(obj):
             break
         obj = new_obj
     else:
+        from _pytest._io.saferepr import saferepr
+
         raise ValueError(
             ("could not find real function of {start}\nstopped at {current}").format(
                 start=saferepr(start_obj), current=saferepr(obj)
@@ -357,6 +358,19 @@ def overload(f):  # noqa: F811
         return f
 
 
+if TYPE_CHECKING:
+    if sys.version_info >= (3, 8):
+        from typing import final as final
+    else:
+        from typing_extensions import final as final
+elif sys.version_info >= (3, 8):
+    from typing import final as final
+else:
+
+    def final(f):  # noqa: F811
+        return f
+
+
 if getattr(attr, "__version_info__", ()) >= (19, 2):
     ATTRS_EQ_FIELD = "eq"
 else:

src/_pytest/config/__init__.py

@@ -43,6 +43,7 @@
 from _pytest._code import ExceptionInfo
 from _pytest._code import filter_traceback
 from _pytest._io import TerminalWriter
+from _pytest.compat import final
 from _pytest.compat import importlib_metadata
 from _pytest.compat import TYPE_CHECKING
 from _pytest.outcomes import fail
@@ -76,6 +77,7 @@
 hookspec = HookspecMarker("pytest")
 
 
+@final
 class ExitCode(enum.IntEnum):
     """Encodes the valid exit codes by pytest.
 
@@ -322,6 +324,7 @@ def _prepareconfig(
         raise
 
 
+@final
 class PytestPluginManager(PluginManager):
     """A :py:class:`pluggy.PluginManager <pluggy.PluginManager>` with
     additional pytest-specific functionality:
@@ -815,6 +818,7 @@ def _args_converter(args: Iterable[str]) -> Tuple[str, ...]:
     return tuple(args)
 
 
+@final
 class Config:
     """Access to configuration values, pluginmanager and plugin hooks.
 
@@ -825,6 +829,7 @@ class Config:
         invocation.
     """
 
+    @final
     @attr.s(frozen=True)
     class InvocationParams:
         """Holds parameters passed during :func:`pytest.main`.

src/_pytest/config/argparsing.py

@@ -16,6 +16,7 @@
 import py
 
 import _pytest._io
+from _pytest.compat import final
 from _pytest.compat import TYPE_CHECKING
 from _pytest.config.exceptions import UsageError
 
@@ -26,6 +27,7 @@
 FILE_OR_DIR = "file_or_dir"
 
 
+@final
 class Parser:
     """Parser for command line arguments and ini-file values.
 

src/_pytest/config/exceptions.py

@@ -1,3 +1,7 @@
+from _pytest.compat import final
+
+
+@final
 class UsageError(Exception):
     """Error in pytest usage or invocation."""
 

src/_pytest/fixtures.py

@@ -32,6 +32,7 @@
 from _pytest._io import TerminalWriter
 from _pytest.compat import _format_args
 from _pytest.compat import _PytestWrapper
+from _pytest.compat import final
 from _pytest.compat import get_real_func
 from _pytest.compat import get_real_method
 from _pytest.compat import getfuncargnames
@@ -730,6 +731,7 @@ def __repr__(self) -> str:
         return "<FixtureRequest for %r>" % (self.node)
 
 
+@final
 class SubRequest(FixtureRequest):
     """A sub request for handling getting a fixture from a test function/fixture."""
 
@@ -796,6 +798,7 @@ def scope2index(scope: str, descr: str, where: Optional[str] = None) -> int:
         )
 
 
+@final
 class FixtureLookupError(LookupError):
     """Could not return a requested fixture (missing or invalid)."""
 
@@ -952,6 +955,7 @@ def _eval_scope_callable(
     return result
 
 
+@final
 class FixtureDef(Generic[_FixtureValue]):
     """A container for a factory definition."""
 
@@ -1161,6 +1165,7 @@ def result(*args, **kwargs):
     return result
 
 
+@final
 @attr.s(frozen=True)
 class FixtureFunctionMarker:
     scope = attr.ib(type="Union[_Scope, Callable[[str, Config], _Scope]]")

src/_pytest/logging.py

@@ -19,6 +19,7 @@
 from _pytest import nodes
 from _pytest._io import TerminalWriter
 from _pytest.capture import CaptureManager
+from _pytest.compat import final
 from _pytest.compat import nullcontext
 from _pytest.config import _strtobool
 from _pytest.config import Config
@@ -339,6 +340,7 @@ def handleError(self, record: logging.LogRecord) -> None:
             raise
 
 
+@final
 class LogCaptureFixture:
     """Provides access and control of log capturing."""
 

src/_pytest/main.py

@@ -21,6 +21,7 @@
 
 import _pytest._code
 from _pytest import nodes
+from _pytest.compat import final
 from _pytest.compat import overload
 from _pytest.compat import TYPE_CHECKING
 from _pytest.config import Config
@@ -435,6 +436,7 @@ def __missing__(self, path: Path) -> str:
         return r
 
 
+@final
 class Session(nodes.FSCollector):
     Interrupted = Interrupted
     Failed = Failed

src/_pytest/mark/structures.py

@@ -20,6 +20,7 @@
 
 from .._code import getfslineno
 from ..compat import ascii_escaped
+from ..compat import final
 from ..compat import NOTSET
 from ..compat import NotSetType
 from ..compat import overload
@@ -199,6 +200,7 @@ def _for_parametrize(
         return argnames, parameters
 
 
+@final
 @attr.s(frozen=True)
 class Mark:
     #: Name of the mark.
@@ -452,6 +454,7 @@ def __call__(  # type: ignore[override]
             ...
 
 
+@final
 class MarkGenerator:
     """Factory for :class:`MarkDecorator` objects - exposed as
     a ``pytest.mark`` singleton instance.
@@ -525,6 +528,7 @@ def __getattr__(self, name: str) -> MarkDecorator:
 
 
 # TODO(py36): inherit from typing.MutableMapping[str, Any].
+@final
 class NodeKeywords(collections.abc.MutableMapping):  # type: ignore[type-arg]
     def __init__(self, node: "Node") -> None:
         self.node = node

src/_pytest/monkeypatch.py

@@ -14,6 +14,7 @@
 from typing import Union
 
 import pytest
+from _pytest.compat import final
 from _pytest.compat import overload
 from _pytest.fixtures import fixture
 from _pytest.pathlib import Path
@@ -110,6 +111,7 @@ def __repr__(self) -> str:
 notset = Notset()
 
 
+@final
 class MonkeyPatch:
     """Object returned by the ``monkeypatch`` fixture keeping a record of
     setattr/item/env/syspath changes."""

src/_pytest/pytester.py

@@ -28,6 +28,7 @@
 from _pytest import timing
 from _pytest._code import Source
 from _pytest.capture import _get_multicapture
+from _pytest.compat import final
 from _pytest.compat import overload
 from _pytest.compat import TYPE_CHECKING
 from _pytest.config import _PluggyPlugin
@@ -597,6 +598,7 @@ def restore(self) -> None:
         sys.path[:], sys.meta_path[:] = self.__saved
 
 
+@final
 class Testdir:
     """Temporary test directory with tools to test/run pytest itself.
 

src/_pytest/python.py

@@ -37,6 +37,7 @@
 from _pytest._io import TerminalWriter
 from _pytest._io.saferepr import saferepr
 from _pytest.compat import ascii_escaped
+from _pytest.compat import final
 from _pytest.compat import get_default_arg_names
 from _pytest.compat import get_real_func
 from _pytest.compat import getimfunc
@@ -864,6 +865,7 @@ def hasnew(obj: object) -> bool:
     return False
 
 
+@final
 class CallSpec2:
     def __init__(self, metafunc: "Metafunc") -> None:
         self.metafunc = metafunc
@@ -924,6 +926,7 @@ def setmulti2(
         self.marks.extend(normalize_mark_list(marks))
 
 
+@final
 class Metafunc:
     """Objects passed to the :func:`pytest_generate_tests <_pytest.hookspec.pytest_generate_tests>` hook.
 

src/_pytest/python_api.py

@@ -17,6 +17,7 @@
 from typing import Union
 
 import _pytest._code
+from _pytest.compat import final
 from _pytest.compat import overload
 from _pytest.compat import STRING_TYPES
 from _pytest.compat import TYPE_CHECKING
@@ -699,6 +700,7 @@ def raises(  # noqa: F811
 raises.Exception = fail.Exception  # type: ignore
 
 
+@final
 class RaisesContext(Generic[_E]):
     def __init__(
         self,

src/_pytest/recwarn.py

@@ -13,6 +13,7 @@
 from typing import TypeVar
 from typing import Union
 
+from _pytest.compat import final
 from _pytest.compat import overload
 from _pytest.compat import TYPE_CHECKING
 from _pytest.fixtures import fixture
@@ -228,6 +229,7 @@ def __exit__(
         self._entered = False
 
 
+@final
 class WarningsChecker(WarningsRecorder):
     def __init__(
         self,

src/_pytest/reports.py

@@ -26,6 +26,7 @@
 from _pytest._code.code import ReprTraceback
 from _pytest._code.code import TerminalRepr
 from _pytest._io import TerminalWriter
+from _pytest.compat import final
 from _pytest.compat import TYPE_CHECKING
 from _pytest.config import Config
 from _pytest.nodes import Collector
@@ -225,6 +226,7 @@ def _report_unserialization_failure(
     raise RuntimeError(stream.getvalue())
 
 
+@final
 class TestReport(BaseReport):
     """Basic test report object (also used for setup and teardown calls if
     they fail)."""
@@ -333,6 +335,7 @@ def from_item_and_call(cls, item: Item, call: "CallInfo[None]") -> "TestReport":
         )
 
 
+@final
 class CollectReport(BaseReport):
     """Collection report object."""