typing: set no_implicit_reexport

In Python, if module A defines a name `name`, and module B does `import
name from A`, then another module C can `import name from B`.

Sometimes it is intentional -- module B is meant to "reexport" `name`.
But sometimes it is just confusion/inconsistency on where `name` should
be imported from.

mypy has a flag `--no-implicit-reexport` which puts some order into
this. A name can only be imported from a module if

1. The module defines the name
2. The module's `__all__` includes the name
3. The module imports the name as `from ... import .. as name`.

This flag is included in mypy's `--strict` flag.

I like this flag, but I realize it is a bit controversial, and in
particular item 3 above is a bit unfriendly to contributors who don't
know about it. So I didn't intend to add it to pytest.

But while investigating issue 7589 I came upon mypy issue 8754 which
causes `--no-implicit-reexport` to leak into installed libraries and
causes some unexpected typing differences *in pytest* if the user uses
this flag.

Since the diff mostly makes sense, let's just conform to it.

setup.cfg

@@ -104,3 +104,4 @@ strict_equality = True
 warn_redundant_casts = True
 warn_return_any = True
 warn_unused_configs = True
+no_implicit_reexport = True

src/_pytest/_code/__init__.py

@@ -4,9 +4,9 @@ from .code import ExceptionInfo
 from .code import filter_traceback
 from .code import Frame
 from .code import getfslineno
-from .code import getrawcode
 from .code import Traceback
 from .code import TracebackEntry
+from .source import getrawcode
 from .source import Source
 
 __all__ = [

src/_pytest/compat.py

@@ -14,7 +14,7 @@ from typing import Any
 from typing import Callable
 from typing import Generic
 from typing import Optional
-from typing import overload
+from typing import overload as overload
 from typing import Tuple
 from typing import TypeVar
 from typing import Union
@@ -208,7 +208,7 @@ if sys.version_info < (3, 7):
 
 
 else:
-    from contextlib import nullcontext  # noqa
+    from contextlib import nullcontext as nullcontext  # noqa: F401
 
 
 def get_default_arg_names(function: Callable[..., Any]) -> Tuple[str, ...]:
@@ -363,7 +363,7 @@ else:
 
 
 if sys.version_info >= (3, 8):
-    from functools import cached_property
+    from functools import cached_property as cached_property
 else:
 
     class cached_property(Generic[_S, _T]):

src/_pytest/config/__init__.py

@@ -35,8 +35,8 @@ from pluggy import PluginManager
 import _pytest._code
 import _pytest.deprecated
 import _pytest.hookspec  # the extension point definitions
-from .exceptions import PrintHelp
-from .exceptions import UsageError
+from .exceptions import PrintHelp as PrintHelp
+from .exceptions import UsageError as UsageError
 from .findpaths import determine_setup
 from _pytest._code import ExceptionInfo
 from _pytest._code import filter_traceback

src/_pytest/mark/__init__.py

@@ -28,7 +28,14 @@ if TYPE_CHECKING:
     from _pytest.nodes import Item
 
 
-__all__ = ["Mark", "MarkDecorator", "MarkGenerator", "get_empty_parameterset_mark"]
+__all__ = [
+    "MARK_GEN",
+    "Mark",
+    "MarkDecorator",
+    "MarkGenerator",
+    "ParameterSet",
+    "get_empty_parameterset_mark",
+]
 
 
 old_mark_config_key = StoreKey[Optional[Config]]()

src/_pytest/python.py

@@ -32,6 +32,7 @@ from _pytest import nodes
 from _pytest._code import filter_traceback
 from _pytest._code import getfslineno
 from _pytest._code.code import ExceptionInfo
+from _pytest._code.code import TerminalRepr
 from _pytest._io import TerminalWriter
 from _pytest._io.saferepr import saferepr
 from _pytest.compat import ascii_escaped
@@ -66,7 +67,6 @@ from _pytest.pathlib import import_path
 from _pytest.pathlib import ImportPathMismatchError
 from _pytest.pathlib import parts
 from _pytest.pathlib import visit
-from _pytest.reports import TerminalRepr
 from _pytest.warning_types import PytestCollectionWarning
 from _pytest.warning_types import PytestUnhandledCoroutineWarning
 
@@ -581,7 +581,7 @@ class Module(nodes.File, PyCollector):
                 "Traceback:\n"
                 "{traceback}".format(fspath=self.fspath, traceback=formatted_tb)
             ) from e
-        except _pytest.runner.Skipped as e:
+        except skip.Exception as e:
             if e.allow_module_level:
                 raise
             raise self.CollectError(

testing/python/collect.py

@@ -1018,7 +1018,7 @@ class TestTracebackCutting:
         See: https://bitbucket.org/pytest-dev/py/issues/71
         This fixes #995.
         """
-        from _pytest.python import filter_traceback
+        from _pytest._code import filter_traceback
 
         try:
             ns = {}  # type: Dict[str, Any]
@@ -1038,7 +1038,7 @@ class TestTracebackCutting:
         In this case, one of the files in the traceback no longer exists.
         This fixes #1133.
         """
-        from _pytest.python import filter_traceback
+        from _pytest._code import filter_traceback
 
         testdir.syspathinsert()
         testdir.makepyfile(

testing/python/fixtures.py

@@ -3,6 +3,7 @@ import textwrap
 
 import pytest
 from _pytest import fixtures
+from _pytest.compat import getfuncargnames
 from _pytest.config import ExitCode
 from _pytest.fixtures import FixtureRequest
 from _pytest.pathlib import Path
@@ -15,22 +16,22 @@ def test_getfuncargnames_functions():
     def f():
         raise NotImplementedError()
 
-    assert not fixtures.getfuncargnames(f)
+    assert not getfuncargnames(f)
 
     def g(arg):
         raise NotImplementedError()
 
-    assert fixtures.getfuncargnames(g) == ("arg",)
+    assert getfuncargnames(g) == ("arg",)
 
     def h(arg1, arg2="hello"):
         raise NotImplementedError()
 
-    assert fixtures.getfuncargnames(h) == ("arg1",)
+    assert getfuncargnames(h) == ("arg1",)
 
     def j(arg1, arg2, arg3="hello"):
         raise NotImplementedError()
 
-    assert fixtures.getfuncargnames(j) == ("arg1", "arg2")
+    assert getfuncargnames(j) == ("arg1", "arg2")
 
 
 def test_getfuncargnames_methods():
@@ -40,7 +41,7 @@ def test_getfuncargnames_methods():
         def f(self, arg1, arg2="hello"):
             raise NotImplementedError()
 
-    assert fixtures.getfuncargnames(A().f) == ("arg1",)
+    assert getfuncargnames(A().f) == ("arg1",)
 
 
 def test_getfuncargnames_staticmethod():
@@ -51,7 +52,7 @@ def test_getfuncargnames_staticmethod():
         def static(arg1, arg2, x=1):
             raise NotImplementedError()
 
-    assert fixtures.getfuncargnames(A.static, cls=A) == ("arg1", "arg2")
+    assert getfuncargnames(A.static, cls=A) == ("arg1", "arg2")
 
 
 def test_getfuncargnames_partial():
@@ -64,7 +65,7 @@ def test_getfuncargnames_partial():
     class T:
         test_ok = functools.partial(check, i=2)
 
-    values = fixtures.getfuncargnames(T().test_ok, name="test_ok")
+    values = getfuncargnames(T().test_ok, name="test_ok")
     assert values == ("arg1", "arg2")
 
 
@@ -78,7 +79,7 @@ def test_getfuncargnames_staticmethod_partial():
     class T:
         test_ok = staticmethod(functools.partial(check, i=2))
 
-    values = fixtures.getfuncargnames(T().test_ok, name="test_ok")
+    values = getfuncargnames(T().test_ok, name="test_ok")
     assert values == ("arg1", "arg2")
 
 

testing/python/integration.py

@@ -1,8 +1,8 @@
 from typing import Any
 
 import pytest
-from _pytest import python
 from _pytest import runner
+from _pytest._code import getfslineno
 
 
 class TestOEJSKITSpecials:
@@ -87,8 +87,8 @@ def test_wrapped_getfslineno() -> None:
     def wrapped_func(x, y, z):
         pass
 
-    fs, lineno = python.getfslineno(wrapped_func)
-    fs2, lineno2 = python.getfslineno(wrap)
+    fs, lineno = getfslineno(wrapped_func)
+    fs2, lineno2 = getfslineno(wrap)
     assert lineno > lineno2, "getfslineno does not unwrap correctly"
 
 

testing/python/metafunc.py

@@ -19,6 +19,8 @@ from hypothesis import strategies
 import pytest
 from _pytest import fixtures
 from _pytest import python
+from _pytest.compat import _format_args
+from _pytest.compat import getfuncargnames
 from _pytest.outcomes import fail
 from _pytest.pytester import Testdir
 from _pytest.python import _idval
@@ -41,7 +43,7 @@ class TestMetafunc:
             obj = attr.ib()
             _nodeid = attr.ib()
 
-        names = fixtures.getfuncargnames(func)
+        names = getfuncargnames(func)
         fixtureinfo = FuncFixtureInfoMock(names)  # type: Any
         definition = DefinitionMock._create(func, "mock::nodeid")  # type: Any
         return python.Metafunc(definition, fixtureinfo, config)
@@ -954,22 +956,22 @@ class TestMetafunc:
         def function1():
             pass
 
-        assert fixtures._format_args(function1) == "()"
+        assert _format_args(function1) == "()"
 
         def function2(arg1):
             pass
 
-        assert fixtures._format_args(function2) == "(arg1)"
+        assert _format_args(function2) == "(arg1)"
 
         def function3(arg1, arg2="qwe"):
             pass
 
-        assert fixtures._format_args(function3) == "(arg1, arg2='qwe')"
+        assert _format_args(function3) == "(arg1, arg2='qwe')"
 
         def function4(arg1, *args, **kwargs):
             pass
 
-        assert fixtures._format_args(function4) == "(arg1, *args, **kwargs)"
+        assert _format_args(function4) == "(arg1, *args, **kwargs)"
 
 
 class TestMetafuncFunctional:

testing/test_mark.py

@@ -4,8 +4,8 @@ from unittest import mock
 
 import pytest
 from _pytest.config import ExitCode
-from _pytest.mark import EMPTY_PARAMETERSET_OPTION
 from _pytest.mark import MarkGenerator as Mark
+from _pytest.mark.structures import EMPTY_PARAMETERSET_OPTION
 from _pytest.nodes import Collector
 from _pytest.nodes import Node