Fix typing alias

ChangeLog

@@ -15,6 +15,15 @@ Release Date: 2021-02-28
 
 * Improve typing.TypedDict inference
 
+* Fix the `Duplicates found in MROs` false positive.
+
+  Closes #905
+  Closes PyCQA/pylint#2717
+  Closes PyCQA/pylint#3247
+  Closes PyCQA/pylint#4093
+  Closes PyCQA/pylint#4131
+  Closes PyCQA/pylint#4145
+
 
 What's New in astroid 2.5?
 ============================

astroid/brain/brain_typing.py

@@ -8,17 +8,21 @@
 """Astroid hooks for typing.py support."""
 import sys
 import typing
+from functools import lru_cache
 
 from astroid import (
     MANAGER,
     UseInferenceDefault,
     extract_node,
     inference_tip,
+    node_classes,
     nodes,
     context,
     InferenceError,
 )
+import astroid
 
+PY37 = sys.version_info[:2] >= (3, 7)
 PY39 = sys.version_info[:2] >= (3, 9)
 
 TYPING_NAMEDTUPLE_BASENAMES = {"NamedTuple", "typing.NamedTuple"}
@@ -112,6 +116,98 @@ def infer_typedDict(  # pylint: disable=invalid-name
     node.root().locals["TypedDict"] = [class_def]
 
 
+GET_ITEM_TEMPLATE = """
+@classmethod
+def __getitem__(cls, value):
+    return cls
+"""
+
+ABC_METACLASS_TEMPLATE = """
+from abc import ABCMeta
+ABCMeta
+"""
+
+
+@lru_cache()
+def create_typing_metaclass():
+    #  Needs to mock the __getitem__ class method so that
+    #  MutableSet[T] is acceptable
+    func_to_add = extract_node(GET_ITEM_TEMPLATE)
+
+    abc_meta = next(extract_node(ABC_METACLASS_TEMPLATE).infer())
+    typing_meta = nodes.ClassDef(
+        name="ABCMeta_typing",
+        lineno=abc_meta.lineno,
+        col_offset=abc_meta.col_offset,
+        parent=abc_meta.parent,
+    )
+    typing_meta.postinit(
+        bases=[extract_node(ABC_METACLASS_TEMPLATE)], body=[], decorators=None
+    )
+    typing_meta.locals["__getitem__"] = [func_to_add]
+    return typing_meta
+
+
+def _looks_like_typing_alias(node: nodes.Call) -> bool:
+    """
+    Returns True if the node corresponds to a call to _alias function.
+    For example :
+
+    MutableSet = _alias(collections.abc.MutableSet, T)
+
+    :param node: call node
+    """
+    return (
+        isinstance(node, nodes.Call)
+        and isinstance(node.func, nodes.Name)
+        and node.func.name == "_alias"
+        and isinstance(node.args[0], nodes.Attribute)
+    )
+
+
+def infer_typing_alias(
+    node: nodes.Call, ctx: context.InferenceContext = None
+) -> typing.Optional[node_classes.NodeNG]:
+    """
+    Infers the call to _alias function
+
+    :param node: call node
+    :param context: inference context
+    """
+    if not isinstance(node, nodes.Call):
+        return None
+    res = next(node.args[0].infer(context=ctx))
+
+    if res != astroid.Uninferable and isinstance(res, nodes.ClassDef):
+        class_def = nodes.ClassDef(
+            name=f"{res.name}_typing",
+            lineno=0,
+            col_offset=0,
+            parent=res.parent,
+        )
+        class_def.postinit(
+            bases=[res],
+            body=res.body,
+            decorators=res.decorators,
+            metaclass=create_typing_metaclass(),
+        )
+        return class_def
+
+    if len(node.args) == 2 and isinstance(node.args[0], nodes.Attribute):
+        class_def = nodes.ClassDef(
+            name=node.args[0].attrname,
+            lineno=0,
+            col_offset=0,
+            parent=node.parent,
+        )
+        class_def.postinit(
+            bases=[], body=[], decorators=None, metaclass=create_typing_metaclass()
+        )
+        return class_def
+
+    return None
+
+
 MANAGER.register_transform(
     nodes.Call,
     inference_tip(infer_typing_typevar_or_newtype),
@@ -125,3 +221,6 @@ def infer_typedDict(  # pylint: disable=invalid-name
     MANAGER.register_transform(
         nodes.FunctionDef, infer_typedDict, _looks_like_typedDict
     )
+
+if PY37:
+    MANAGER.register_transform(nodes.Call, infer_typing_alias, _looks_like_typing_alias)

tests/unittest_brain.py

@@ -99,6 +99,11 @@
 import astroid.test_utils as test_utils
 
 
+def assertEqualMro(klass, expected_mro):
+    """Check mro names."""
+    assert [member.name for member in klass.mro()] == expected_mro
+
+
 class HashlibTest(unittest.TestCase):
     def _assert_hashlib_class(self, class_obj):
         self.assertIn("update", class_obj)
@@ -1206,6 +1211,116 @@ class CustomTD(TypedDict):
         assert len(typing_module.locals["TypedDict"]) == 1
         assert inferred_base == typing_module.locals["TypedDict"][0]
 
+    @test_utils.require_version("3.8")
+    def test_typing_alias_type(self):
+        """
+        Test that the type aliased thanks to typing._alias function are
+        correctly inferred.
+        """
+
+        def check_metaclass(node: nodes.ClassDef):
+            meta = node.metaclass()
+            assert isinstance(meta, nodes.ClassDef)
+            assert meta.name == "ABCMeta_typing"
+            assert "ABCMeta" == meta.basenames[0]
+            assert meta.locals.get("__getitem__") is not None
+
+            abc_meta = next(meta.bases[0].infer())
+            assert isinstance(abc_meta, nodes.ClassDef)
+            assert abc_meta.name == "ABCMeta"
+            assert abc_meta.locals.get("__getitem__") is None
+
+        node = builder.extract_node(
+            """
+        from typing import TypeVar, MutableSet
+
+        T = TypeVar("T")
+        MutableSet[T]
+
+        class Derived1(MutableSet[T]):
+            pass
+        """
+        )
+        inferred = next(node.infer())
+        check_metaclass(inferred)
+        assertEqualMro(
+            inferred,
+            [
+                "Derived1",
+                "MutableSet_typing",
+                "MutableSet",
+                "Set",
+                "Collection",
+                "Sized",
+                "Iterable",
+                "Container",
+                "object",
+            ],
+        )
+
+        node = builder.extract_node(
+            """
+        import typing
+        class Derived2(typing.OrderedDict[int, str]):
+            pass
+        """
+        )
+        inferred = next(node.infer())
+        check_metaclass(inferred)
+        assertEqualMro(
+            inferred,
+            [
+                "Derived2",
+                "OrderedDict_typing",
+                "OrderedDict",
+                "dict",
+                "object",
+            ],
+        )
+
+        node = builder.extract_node(
+            """
+        import typing
+        class Derived3(typing.Pattern[str]):
+            pass
+        """
+        )
+        inferred = next(node.infer())
+        check_metaclass(inferred)
+        assertEqualMro(
+            inferred,
+            [
+                "Derived3",
+                "Pattern",
+                "object",
+            ],
+        )
+
+    @test_utils.require_version("3.8")
+    def test_typing_alias_side_effects(self):
+        """Test that typing._alias changes doesn't have unwanted consequences."""
+        node = builder.extract_node(
+            """
+        import typing
+        import collections.abc
+
+        class Derived(collections.abc.Iterator[int]):
+            pass
+        """
+        )
+        inferred = next(node.infer())
+        assert inferred.metaclass() is None  # Should this be ABCMeta?
+        assertEqualMro(
+            inferred,
+            [
+                "Derived",
+                # Should this be more?
+                # "Iterator_typing"?
+                # "Iterator",
+                # "object",
+            ],
+        )
+
 
 class ReBrainTest(unittest.TestCase):
     def test_regex_flags(self):