Clean typing.Generic from mro

ChangeLog

@@ -19,6 +19,8 @@ Release Date: TBA
 
 * Use ``inference_tip`` for ``typing.TypedDict`` brain.
 
+* Fix mro for classes that inherit from typing.Generic
+
 * Add inference tip for typing.Generic and typing.Annotated with ``__class_getitem__``
 
   Closes PyCQA/pylint#2822

astroid/scoped_nodes.py

@@ -103,6 +103,39 @@ def _c3_merge(sequences, cls, context):
     return None
 
 
+def clean_typing_generic_mro(sequences: List[List["ClassDef"]]) -> None:
+    """typing.Generic is allowed to appear multiple times in the initial mro.
+    The final one however, MUST only contain ONE occurrence.
+
+    This method will check if the Generic is in the inferred_bases, but also
+    part of the bases_mro. If true, remove it from the inferred_bases
+    as well as its entry the bases_mro.
+
+    Format sequences: [[self]] + bases_mro + [inferred_bases]
+    """
+    pos_generic_in_main_bases = -1
+    # Check if part of inferred_bases
+    for i, base in enumerate(sequences[-1]):
+        if base.qname() == "typing.Generic":
+            pos_generic_in_main_bases = i
+            break
+    else:
+        return
+    # Check if also part of the bases_mro
+    # Ignore entry for typing.Generic
+    for i, seq in enumerate(sequences[1:-1]):
+        if i == pos_generic_in_main_bases:
+            continue
+        if any(base.qname() == "typing.Generic" for base in seq):
+            break
+    else:
+        return
+    # Found multiple Generics in mro, remove entry from inferred_bases
+    # and the coresponding one from bases_mro
+    sequences[-1].pop(pos_generic_in_main_bases)
+    sequences.pop(pos_generic_in_main_bases + 1)
+
+
 def clean_duplicates_mro(sequences, cls, context):
     for sequence in sequences:
         names = [
@@ -2924,6 +2957,7 @@ def _compute_mro(self, context=None):
 
         unmerged_mro = [[self]] + bases_mro + [inferred_bases]
         unmerged_mro = list(clean_duplicates_mro(unmerged_mro, self, context))
+        clean_typing_generic_mro(unmerged_mro)
         return _c3_merge(unmerged_mro, self, context)
 
     def mro(self, context=None) -> List["ClassDef"]:

tests/unittest_scoped_nodes.py

@@ -1275,6 +1275,9 @@ class NodeBase(object):
     def assertEqualMro(self, klass, expected_mro):
         self.assertEqual([member.name for member in klass.mro()], expected_mro)
 
+    def assertEqualMroQName(self, klass, expected_mro):
+        self.assertEqual([member.qname() for member in klass.mro()], expected_mro)
+
     @unittest.skipUnless(HAS_SIX, "These tests require the six library")
     def test_with_metaclass_mro(self):
         astroid = builder.parse(
@@ -1438,6 +1441,142 @@ class C(scope.A, scope.B):
         )
         self.assertEqualMro(cls, ["C", "A", "B", "object"])
 
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_1(self):
+        cls = builder.extract_node(
+            """
+        import typing
+        T = typing.TypeVar('T')
+        class A(typing.Generic[T]): ...
+        class B: ...
+        class C(A[T], B): ...
+        """
+        )
+        self.assertEqualMroQName(
+            cls, [".C", ".A", "typing.Generic", ".B", "builtins.object"]
+        )
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_2(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T = TypeVar('T')
+        class A: ...
+        class B(Generic[T]): ...
+        class C(Generic[T], A, B[T]): ...
+        """
+        )
+        self.assertEqualMroQName(
+            cls, [".C", ".A", ".B", "typing.Generic", "builtins.object"]
+        )
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_3(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T = TypeVar('T')
+        class A: ...
+        class B(A, Generic[T]): ...
+        class C(Generic[T]): ...
+        class D(B[T], C[T], Generic[T]): ...
+        """
+        )
+        self.assertEqualMroQName(
+            cls, [".D", ".B", ".A", ".C", "typing.Generic", "builtins.object"]
+        )
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_4(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T = TypeVar('T')
+        class A: ...
+        class B(Generic[T]): ...
+        class C(A, Generic[T], B[T]): ...
+        """
+        )
+        self.assertEqualMroQName(
+            cls, [".C", ".A", ".B", "typing.Generic", "builtins.object"]
+        )
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_5(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T1 = TypeVar('T1')
+        T2 = TypeVar('T2')
+        class A(Generic[T1]): ...
+        class B(Generic[T2]): ...
+        class C(A[T1], B[T2]): ...
+        """
+        )
+        self.assertEqualMroQName(
+            cls, [".C", ".A", ".B", "typing.Generic", "builtins.object"]
+        )
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_6(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic as TGeneric, TypeVar
+        T = TypeVar('T')
+        class Generic: ...
+        class A(Generic): ...
+        class B(TGeneric[T]): ...
+        class C(A, B[T]): ...
+        """
+        )
+        self.assertEqualMroQName(
+            cls, [".C", ".A", ".Generic", ".B", "typing.Generic", "builtins.object"]
+        )
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_7(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T = TypeVar('T')
+        class A(): ...
+        class B(Generic[T]): ...
+        class C(A, B[T]): ...
+        class D: ...
+        class E(C[str], D): ...
+        """
+        )
+        self.assertEqualMroQName(
+            cls, [".E", ".C", ".A", ".B", "typing.Generic", ".D", "builtins.object"]
+        )
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_error_1(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T1 = TypeVar('T1')
+        T2 = TypeVar('T2')
+        class A(Generic[T1], Generic[T2]): ...
+        """
+        )
+        with self.assertRaises(DuplicateBasesError) as ex:
+            cls.mro()
+
+    @test_utils.require_version(minver="3.7")
+    def test_mro_generic_error_2(self):
+        cls = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T = TypeVar('T')
+        class A(Generic[T]): ...
+        class B(A[T], A[T]): ...
+        """
+        )
+        with self.assertRaises(DuplicateBasesError) as ex:
+            cls.mro()
+
     def test_generator_from_infer_call_result_parent(self):
         func = builder.extract_node(
             """