Type improvements

Annotate MockerFixture.patch(). Without an explicit annotations, mypy
and other type checkers can't determine the proper type and assume Any.

MockerFixture.patch() can return an arbitrary type if either new or
new_callable is provided. Add overloads to handle these cases.

CHANGELOG.rst

@@ -10,6 +10,12 @@
 
   Note however that this is just a stop gap measure, and new code should use ``MockerFixture`` for type annotations.
 
+* Improved typing for ``MockerFixture.patch``  (`#201`_). Thanks `@srittau`_ for the PR.
+
+.. _@srittau: https://github.com/srittau
+.. _#201: https://github.com/pytest-dev/pytest-mock/pull/201
+
+
 3.3.0 (2020-08-21)
 ------------------
 

src/pytest_mock/plugin.py

@@ -1,6 +1,6 @@
 import builtins
 import unittest.mock
-from typing import cast, Generator, Mapping, Iterable, Tuple
+from typing import cast, overload, Generator, Mapping, Iterable, Tuple, TypeVar
 from typing import Any
 from typing import Callable
 from typing import Dict
@@ -17,6 +17,8 @@
 
 import pytest
 
+_T = TypeVar("_T")
+
 
 def _get_mock_module(config):
     """
@@ -50,7 +52,9 @@ def __init__(self, config: Any) -> None:
         self._patches = []  # type: List[Any]
         self._mocks = []  # type: List[Any]
         self.mock_module = mock_module = _get_mock_module(config)
-        self.patch = self._Patcher(self._patches, self._mocks, mock_module)
+        self.patch = self._Patcher(
+            self._patches, self._mocks, mock_module
+        )  # type: MockerFixture._Patcher
         # aliases for convenience
         self.Mock = mock_module.Mock
         self.MagicMock = mock_module.MagicMock
@@ -254,6 +258,63 @@ def dict(
                 **kwargs
             )
 
+        @overload
+        def __call__(
+            self,
+            target: str,
+            new: None = ...,
+            spec: Optional[builtins.object] = ...,
+            create: bool = ...,
+            spec_set: Optional[builtins.object] = ...,
+            autospec: Optional[builtins.object] = ...,
+            new_callable: None = ...,
+            **kwargs: Any
+        ) -> unittest.mock.MagicMock:
+            ...
+
+        @overload
+        def __call__(
+            self,
+            target: str,
+            new: _T,
+            spec: Optional[builtins.object] = ...,
+            create: bool = ...,
+            spec_set: Optional[builtins.object] = ...,
+            autospec: Optional[builtins.object] = ...,
+            new_callable: None = ...,
+            **kwargs: Any
+        ) -> _T:
+            ...
+
+        @overload
+        def __call__(
+            self,
+            target: str,
+            new: None,
+            spec: Optional[builtins.object],
+            create: bool,
+            spec_set: Optional[builtins.object],
+            autospec: Optional[builtins.object],
+            new_callable: Callable[[], _T],
+            **kwargs: Any
+        ) -> _T:
+            ...
+
+        @overload
+        def __call__(
+            self,
+            target: str,
+            new: None = ...,
+            spec: Optional[builtins.object] = ...,
+            create: bool = ...,
+            spec_set: Optional[builtins.object] = ...,
+            autospec: Optional[builtins.object] = ...,
+            *,
+            new_callable: Callable[[], _T],
+            **kwargs: Any
+        ) -> _T:
+            ...
+
         def __call__(
             self,
             target: str,
@@ -262,9 +323,9 @@ def __call__(
             create: bool = False,
             spec_set: Optional[builtins.object] = None,
             autospec: Optional[builtins.object] = None,
-            new_callable: Optional[builtins.object] = None,
+            new_callable: Optional[Callable[[], Any]] = None,
             **kwargs: Any
-        ) -> unittest.mock.MagicMock:
+        ) -> Any:
             """API to mock.patch"""
             if new is self.DEFAULT:
                 new = self.mock_module.DEFAULT