Enable check_untyped_defs mypy option for src/

This option checks even functions which are not annotated. It's a good
step to ensure that existing type annotation are correct.

In a Pareto fashion, the last few holdouts are always the ugliest,
beware.

9 files changed, 65 insertions, 31 deletions

diff --git a/setup.cfg b/setup.cfg
index a7dd6d1c3..a42ae68ae 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -98,3 +98,6 @@ strict_equality = True
 warn_redundant_casts = True
 warn_return_any = True
 warn_unused_configs = True
+
+[mypy-_pytest.*]
+check_untyped_defs = True
diff --git a/src/_pytest/capture.py b/src/_pytest/capture.py
index bcc16ceb6..98ba878b3 100644
--- a/src/_pytest/capture.py
+++ b/src/_pytest/capture.py
@@ -519,10 +519,11 @@ class MultiCapture:
     def pop_outerr_to_orig(self):
         """ pop current snapshot out/err capture and flush to orig streams. """
         out, err = self.readouterr()
+        # TODO: Fix type ignores.
         if out:
-            self.out.writeorg(out)
+            self.out.writeorg(out)  # type: ignore[union-attr] # noqa: F821
         if err:
-            self.err.writeorg(err)
+            self.err.writeorg(err)  # type: ignore[union-attr] # noqa: F821
         return out, err
 
     def suspend_capturing(self, in_: bool = False) -> None:
@@ -542,7 +543,8 @@ class MultiCapture:
         if self.err:
             self.err.resume()
         if self._in_suspended:
-            self.in_.resume()
+            # TODO: Fix type ignore.
+            self.in_.resume()  # type: ignore[union-attr] # noqa: F821
             self._in_suspended = False
 
     def stop_capturing(self) -> None:
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index ff6aee744..27083900d 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -974,7 +974,7 @@ class Config:
                 self._mark_plugins_for_rewrite(hook)
         _warn_about_missing_assertion(mode)
 
-    def _mark_plugins_for_rewrite(self, hook):
+    def _mark_plugins_for_rewrite(self, hook) -> None:
         """
         Given an importhook, mark for rewrite any top-level
         modules or packages in the distribution package for
@@ -989,7 +989,9 @@ class Config:
         package_files = (
             str(file)
             for dist in importlib_metadata.distributions()
-            if any(ep.group == "pytest11" for ep in dist.entry_points)
+            # Type ignored due to missing stub:
+            # https://github.com/python/typeshed/pull/3795
+            if any(ep.group == "pytest11" for ep in dist.entry_points)  # type: ignore
             for file in dist.files or []
         )
 
diff --git a/src/_pytest/fixtures.py b/src/_pytest/fixtures.py
index 8aa5d73a8..fa7e3e1df 100644
--- a/src/_pytest/fixtures.py
+++ b/src/_pytest/fixtures.py
@@ -721,7 +721,9 @@ class FixtureRequest:
             # this might also be a non-function Item despite its attribute name
             return self._pyfuncitem
         if scope == "package":
-            node = get_scope_package(self._pyfuncitem, self._fixturedef)
+            # FIXME: _fixturedef is not defined on FixtureRequest (this class),
+            # but on FixtureRequest (a subclass).
+            node = get_scope_package(self._pyfuncitem, self._fixturedef)  # type: ignore[attr-defined] # noqa: F821
         else:
             node = get_scope_node(self._pyfuncitem, scope)
         if node is None and scope == "class":
@@ -1158,7 +1160,7 @@ def wrap_function_to_error_out_if_called_directly(function, fixture_marker):
 
     # keep reference to the original function in our own custom attribute so we don't unwrap
     # further than this point and lose useful wrappings like @mock.patch (#3774)
-    result.__pytest_wrapped__ = _PytestWrapper(function)
+    result.__pytest_wrapped__ = _PytestWrapper(function)  # type: ignore[attr-defined] # noqa: F821
 
     return result
 
diff --git a/src/_pytest/nodes.py b/src/_pytest/nodes.py
index eaa48e5de..15f91343f 100644
--- a/src/_pytest/nodes.py
+++ b/src/_pytest/nodes.py
@@ -42,6 +42,8 @@ if TYPE_CHECKING:
 
     # Imported here due to circular import.
     from _pytest.main import Session
+    from _pytest.warning_types import PytestWarning
+
 
 SEP = "/"
 
@@ -118,9 +120,9 @@ class Node(metaclass=NodeMeta):
     def __init__(
         self,
         name: str,
-        parent: Optional["Node"] = None,
+        parent: "Optional[Node]" = None,
         config: Optional[Config] = None,
-        session: Optional["Session"] = None,
+        session: "Optional[Session]" = None,
         fspath: Optional[py.path.local] = None,
         nodeid: Optional[str] = None,
     ) -> None:
@@ -201,7 +203,7 @@ class Node(metaclass=NodeMeta):
     def __repr__(self) -> str:
         return "<{} {}>".format(self.__class__.__name__, getattr(self, "name", None))
 
-    def warn(self, warning):
+    def warn(self, warning: "PytestWarning") -> None:
         """Issue a warning for this item.
 
         Warnings will be displayed after the test session, unless explicitly suppressed
@@ -226,11 +228,9 @@ class Node(metaclass=NodeMeta):
                 )
             )
         path, lineno = get_fslocation_from_item(self)
+        assert lineno is not None
         warnings.warn_explicit(
-            warning,
-            category=None,
-            filename=str(path),
-            lineno=lineno + 1 if lineno is not None else None,
+            warning, category=None, filename=str(path), lineno=lineno + 1,
         )
 
     # methods for ordering nodes
@@ -417,24 +417,26 @@ class Node(metaclass=NodeMeta):
 
 
 def get_fslocation_from_item(
-    item: "Item",
+    node: "Node",
 ) -> Tuple[Union[str, py.path.local], Optional[int]]:
-    """Tries to extract the actual location from an item, depending on available attributes:
+    """Tries to extract the actual location from a node, depending on available attributes:
 
-    * "fslocation": a pair (path, lineno)
-    * "obj": a Python object that the item wraps.
+    * "location": a pair (path, lineno)
+    * "obj": a Python object that the node wraps.
     * "fspath": just a path
 
     :rtype: a tuple of (str|LocalPath, int) with filename and line number.
     """
-    try:
-        return item.location[:2]
-    except AttributeError:
-        pass
-    obj = getattr(item, "obj", None)
+    # See Item.location.
+    location = getattr(
+        node, "location", None
+    )  # type: Optional[Tuple[str, Optional[int], str]]
+    if location is not None:
+        return location[:2]
+    obj = getattr(node, "obj", None)
     if obj is not None:
         return getfslineno(obj)
-    return getattr(item, "fspath", "unknown location"), -1
+    return getattr(node, "fspath", "unknown location"), -1
 
 
 class Collector(Node):
diff --git a/src/_pytest/pytester.py b/src/_pytest/pytester.py
index 60df17b90..754ecc10f 100644
--- a/src/_pytest/pytester.py
+++ b/src/_pytest/pytester.py
@@ -1169,8 +1169,10 @@ class Testdir:
 
         popen = subprocess.Popen(cmdargs, stdout=stdout, stderr=stderr, **kw)
         if stdin is Testdir.CLOSE_STDIN:
+            assert popen.stdin is not None
             popen.stdin.close()
         elif isinstance(stdin, bytes):
+            assert popen.stdin is not None
             popen.stdin.write(stdin)
 
         return popen
diff --git a/src/_pytest/python.py b/src/_pytest/python.py
index 55ed2b164..41dd8b292 100644
--- a/src/_pytest/python.py
+++ b/src/_pytest/python.py
@@ -64,6 +64,7 @@ from _pytest.warning_types import PytestCollectionWarning
 from _pytest.warning_types import PytestUnhandledCoroutineWarning
 
 if TYPE_CHECKING:
+    from typing import Type
     from typing_extensions import Literal
     from _pytest.fixtures import _Scope
 
@@ -256,6 +257,18 @@ def pytest_pycollect_makeitem(collector: "PyCollector", name: str, obj):
 class PyobjMixin:
     _ALLOW_MARKERS = True
 
+    # Function and attributes that the mixin needs (for type-checking only).
+    if TYPE_CHECKING:
+        name = ""  # type: str
+        parent = None  # type: Optional[nodes.Node]
+        own_markers = []  # type: List[Mark]
+
+        def getparent(self, cls: Type[nodes._NodeType]) -> Optional[nodes._NodeType]:
+            ...
+
+        def listchain(self) -> List[nodes.Node]:
+            ...
+
     @property
     def module(self):
         """Python module object this node was collected from (can be None)."""
@@ -292,7 +305,10 @@ class PyobjMixin:
 
     def _getobj(self):
         """Gets the underlying Python object. May be overwritten by subclasses."""
-        return getattr(self.parent.obj, self.name)
+        # TODO: Improve the type of `parent` such that assert/ignore aren't needed.
+        assert self.parent is not None
+        obj = self.parent.obj  # type: ignore[attr-defined] # noqa: F821
+        return getattr(obj, self.name)
 
     def getmodpath(self, stopatmodule=True, includemodule=False):
         """ return python path relative to the containing module. """
@@ -772,7 +788,10 @@ class Instance(PyCollector):
     # can be removed at node structure reorganization time
 
     def _getobj(self):
-        return self.parent.obj()
+        # TODO: Improve the type of `parent` such that assert/ignore aren't needed.
+        assert self.parent is not None
+        obj = self.parent.obj  # type: ignore[attr-defined] # noqa: F821
+        return obj()
 
     def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         self.session._fixturemanager.parsefactories(self)
@@ -1527,7 +1546,8 @@ class Function(PyobjMixin, nodes.Item):
         return getimfunc(self.obj)
 
     def _getobj(self):
-        return getattr(self.parent.obj, self.originalname)
+        assert self.parent is not None
+        return getattr(self.parent.obj, self.originalname)  # type: ignore[attr-defined]
 
     @property
     def _pyfuncitem(self):
diff --git a/src/_pytest/python_api.py b/src/_pytest/python_api.py
index 29c8af7e2..abace3196 100644
--- a/src/_pytest/python_api.py
+++ b/src/_pytest/python_api.py
@@ -508,7 +508,7 @@ def approx(expected, rel=None, abs=None, nan_ok=False):
     __tracebackhide__ = True
 
     if isinstance(expected, Decimal):
-        cls = ApproxDecimal
+        cls = ApproxDecimal  # type: Type[ApproxBase]
     elif isinstance(expected, Number):
         cls = ApproxScalar
     elif isinstance(expected, Mapping):
@@ -534,7 +534,7 @@ def _is_numpy_array(obj):
     """
     import sys
 
-    np = sys.modules.get("numpy")
+    np = sys.modules.get("numpy")  # type: Any
     if np is not None:
         return isinstance(obj, np.ndarray)
     return False
diff --git a/src/_pytest/recwarn.py b/src/_pytest/recwarn.py
index 58b6fbab9..57034be2a 100644
--- a/src/_pytest/recwarn.py
+++ b/src/_pytest/recwarn.py
@@ -136,8 +136,9 @@ class WarningsRecorder(warnings.catch_warnings):
     Adapted from `warnings.catch_warnings`.
     """
 
-    def __init__(self):
-        super().__init__(record=True)
+    def __init__(self) -> None:
+        # Type ignored due to the way typeshed handles warnings.catch_warnings.
+        super().__init__(record=True)  # type: ignore[call-arg] # noqa: F821
         self._entered = False
         self._list = []  # type: List[warnings.WarningMessage]