[WIP] add type annotations to from_parents and its usages, BROKEN

src/_pytest/doctest.py

@@ -6,6 +6,7 @@
 import traceback
 import warnings
 from contextlib import contextmanager
+from typing import cast
 from typing import Dict
 from typing import List
 from typing import Optional
@@ -14,6 +15,7 @@
 from typing import Union
 
 import pytest
+from _pytest import nodes
 from _pytest import outcomes
 from _pytest._code.code import ExceptionInfo
 from _pytest._code.code import ReprFileLocation
@@ -217,13 +219,21 @@ def __init__(self, name, parent, runner=None, dtest=None):
 
     @classmethod
     def from_parent(  # type: ignore
-        cls, parent: "Union[DoctestTextfile, DoctestModule]", *, name, runner, dtest
-    ):
+        cls: Type[nodes.N],
+        parent: "Union[DoctestTextfile, DoctestModule]",
+        *,
+        name,
+        runner,
+        dtest
+    ) -> nodes.N:
         # incompatible signature due to to imposed limits on sublcass
         """
         the public named constructor
         """
-        return super().from_parent(name=name, parent=parent, runner=runner, dtest=dtest)
+        return cast(
+            nodes.N,
+            super().from_parent(name=name, parent=parent, runner=runner, dtest=dtest),
+        )
 
     def setup(self):
         if self.dtest is not None:

src/_pytest/nodes.py

@@ -2,11 +2,13 @@
 import warnings
 from functools import lru_cache
 from typing import Any
+from typing import cast
 from typing import Dict
 from typing import List
 from typing import Optional
 from typing import Set
 from typing import Tuple
+from typing import TypeVar
 from typing import Union
 
 import py
@@ -30,6 +32,9 @@
 if False:  # TYPE_CHECKING
     # Imported here due to circular import.
     from _pytest.main import Session  # noqa: F401
+    from typing import Type
+
+N = TypeVar("N", bound="Node")
 
 SEP = "/"
 
@@ -144,7 +149,7 @@ def __init__(
                 self._nodeid += "::" + self.name
 
     @classmethod
-    def from_parent(cls, parent: "Node", **kw):
+    def from_parent(cls: Type[N], parent: "Node", **kw) -> N:
         """
         Public Constructor for Nodes
 
@@ -159,7 +164,7 @@ def from_parent(cls, parent: "Node", **kw):
             raise TypeError("config is not a valid argument for from_parent")
         if "session" in kw:
             raise TypeError("session is not a valid argument for from_parent")
-        return cls._create(parent=parent, **kw)
+        return cast(N, cls._create(parent=parent, **kw))
 
     @property
     def ihook(self):

src/_pytest/python.py

@@ -9,9 +9,11 @@
 from collections.abc import Sequence
 from functools import partial
 from textwrap import dedent
+from typing import cast
 from typing import List
 from typing import Optional
 from typing import Tuple
+from typing import Union
 
 import py
 
@@ -45,6 +47,9 @@
 from _pytest.warning_types import PytestCollectionWarning
 from _pytest.warning_types import PytestUnhandledCoroutineWarning
 
+if False:  # TYPE_CHECKING
+    from typing import Type
+
 
 def pyobj_property(name):
     def get(self):
@@ -188,7 +193,7 @@ def path_matches_patterns(path, patterns):
     return any(path.fnmatch(pattern) for pattern in patterns)
 
 
-def pytest_pycollect_makemodule(path, parent):
+def pytest_pycollect_makemodule(path, parent) -> Union["Package", "Module"]:
     if path.basename == "__init__.py":
         return Package.from_parent(parent, fspath=path)
     return Module.from_parent(parent, fspath=path)
@@ -678,11 +683,11 @@ class Class(PyCollector):
     """ Collector for test methods. """
 
     @classmethod
-    def from_parent(cls, parent, *, name, obj=None):
+    def from_parent(cls: Type[nodes.N], parent, *, name, obj=None) -> nodes.N:
         """
         The public constructor
         """
-        return super().from_parent(name=name, parent=parent)
+        return cast(nodes.N, super().from_parent(name=name, parent=parent))
 
     def collect(self):
         if not safe_getattr(self.obj, "__test__", True):

testing/python/collect.py

@@ -277,7 +277,7 @@ def __call__(self, tmpdir):
         )
 
     @staticmethod
-    def make_function(testdir, **kwargs):
+    def make_function(testdir, **kwargs) -> pytest.Function:
         from _pytest.fixtures import FixtureManager
 
         config = testdir.parseconfigure()