Cleanup generic class variable access

Author: ilevkivskyi

mypy/checkmember.py

@@ -45,7 +45,6 @@
     freeze_all_type_vars,
     function_type,
     get_all_type_vars,
-    get_type_vars,
     make_simplified_union,
     supported_self_type,
     tuple_fallback,
@@ -1192,31 +1191,36 @@ def analyze_class_attribute_access(
 
         if isinstance(node.node, Var):
             assert isuper is not None
+            object_type = get_proper_type(mx.self_type)
             # Check if original variable type has type variables. For example:
             #     class C(Generic[T]):
             #         x: T
             #     C.x  # Error, ambiguous access
             #     C[int].x  # Also an error, since C[int] is same as C at runtime
             # Exception is Self type wrapped in ClassVar, that is safe.
+            prohibit_self = not node.node.is_classvar
             def_vars = set(node.node.info.defn.type_vars)
-            if not node.node.is_classvar and node.node.info.self_type:
+            if prohibit_self and node.node.info.self_type:
                 def_vars.add(node.node.info.self_type)
-            # TODO: should we include ParamSpec etc. here (i.e. use get_all_type_vars)?
-            typ_vars = set(get_type_vars(t))
-            if def_vars & typ_vars:
-                # Exception: access on Type[...], including first argument of class methods is OK.
-                if not isinstance(get_proper_type(mx.original_type), TypeType) or node.implicit:
-                    if node.node.is_classvar:
-                        message = message_registry.GENERIC_CLASS_VAR_ACCESS
-                    else:
-                        message = message_registry.GENERIC_INSTANCE_VAR_CLASS_ACCESS
-                    mx.fail(message)
+            # Exception: access on Type[...], including first argument of class methods is OK.
+            prohibit_generic = not isinstance(object_type, TypeType) or node.implicit
+            if prohibit_generic and def_vars & set(get_all_type_vars(t)):
+                if node.node.is_classvar:
+                    message = message_registry.GENERIC_CLASS_VAR_ACCESS
+                else:
+                    message = message_registry.GENERIC_INSTANCE_VAR_CLASS_ACCESS
+                mx.fail(message)
             t = expand_self_type_if_needed(t, mx, node.node, itype, is_class=True)
+            t = expand_type_by_instance(t, isuper)
             # Erase non-mapped variables, but keep mapped ones, even if there is an error.
             # In the above example this means that we infer following types:
             #     C.x -> Any
             #     C[int].x -> int
-            t = erase_typevars(expand_type_by_instance(t, isuper), {tv.id for tv in def_vars})
+            if prohibit_generic:
+                erase_vars = set(itype.type.defn.type_vars)
+                if prohibit_self and itype.type.self_type:
+                    erase_vars.add(itype.type.self_type)
+                t = erase_typevars(t, {tv.id for tv in erase_vars})
 
         is_classmethod = (is_decorated and cast(Decorator, node.node).func.is_class) or (
             isinstance(node.node, SYMBOL_FUNCBASE_TYPES) and node.node.is_class

mypy/message_registry.py

@@ -253,7 +253,6 @@ def with_additional_msg(self, info: str) -> ErrorMessage:
     'Cannot override class variable (previously declared on base class "{}") with instance '
     "variable"
 )
-CLASS_VAR_WITH_TYPEVARS: Final = "ClassVar cannot contain type variables"
 CLASS_VAR_WITH_GENERIC_SELF: Final = "ClassVar cannot contain Self type in generic classes"
 CLASS_VAR_OUTSIDE_OF_CLASS: Final = "ClassVar can only be used for assignments in class body"
 

mypy/semanal.py

@@ -5071,14 +5071,6 @@ def check_classvar(self, s: AssignmentStmt) -> None:
                 node.is_classvar = True
             analyzed = self.anal_type(s.type)
             assert self.type is not None
-            if analyzed is not None and set(get_type_vars(analyzed)) & set(
-                self.type.defn.type_vars
-            ):
-                # This means that we have a type var defined inside of a ClassVar.
-                # This is not allowed by PEP526.
-                # See https://github.com/python/mypy/issues/11538
-
-                self.fail(message_registry.CLASS_VAR_WITH_TYPEVARS, s)
             if (
                 analyzed is not None
                 and self.type.self_type in get_type_vars(analyzed)

test-data/unit/check-classvar.test

@@ -285,7 +285,7 @@ main:3: error: Cannot assign to class variable "x" via instance
 from typing import ClassVar, Generic, TypeVar
 T = TypeVar('T')
 class A(Generic[T]):
-    x: ClassVar[T]  # E: ClassVar cannot contain type variables
+    x: ClassVar[T]  # Error reported at access site
     @classmethod
     def foo(cls) -> T:
         return cls.x  # OK
@@ -308,7 +308,7 @@ from typing import ClassVar, Generic, Tuple, TypeVar, Union, Type
 T = TypeVar('T')
 U = TypeVar('U')
 class A(Generic[T, U]):
-    x: ClassVar[Union[T, Tuple[U, Type[U]]]]  # E: ClassVar cannot contain type variables
+    x: ClassVar[Union[T, Tuple[U, Type[U]]]]  # Error reported at access site
     @classmethod
     def foo(cls) -> Union[T, Tuple[U, Type[U]]]:
         return cls.x  # OK
@@ -343,3 +343,18 @@ class C:
     g: ClassVar[Union[Callable[[C], int], int]] = f
 
 reveal_type(C().g)  # N: Revealed type is "Union[def () -> builtins.int, builtins.int]"
+
+[case testGenericSubclassAccessNoLeak]
+from typing import ClassVar, Generic, TypeVar
+
+T = TypeVar("T")
+class B(Generic[T]):
+    x: T
+    y: ClassVar[T]
+
+class C(B[T]): ...
+
+reveal_type(C.x)  # E: Access to generic instance variables via class is ambiguous \
+                  # N: Revealed type is "Any"
+reveal_type(C.y)  # E: Access to generic class variables is ambiguous \
+                  # N: Revealed type is "Any"

test-data/unit/check-selftype.test

@@ -2219,3 +2219,16 @@ class B:
 class C(A, B):  # OK: both methods take Self
     pass
 [builtins fixtures/tuple.pyi]
+
+[case testSelfTypeClassMethodNotSilentlyErased]
+from typing import ClassVar, Self, Optional
+
+class X:
+    _inst: Optional[Self] = None
+    @classmethod
+    def default(cls) -> Self:
+        reveal_type(cls._inst)  # N: Revealed type is "Union[Self`0, None]"
+        if cls._inst is None:
+            cls._inst = cls()
+        return cls._inst
+[builtins fixtures/tuple.pyi]

test-data/unit/check-typevar-tuple.test

@@ -2628,3 +2628,14 @@ def fn(f: Callable[[*tuple[T]], int]) -> Callable[[*tuple[T]], int]: ...
 def test(*args: Unpack[tuple[T]]) -> int: ...
 reveal_type(fn(test))  # N: Revealed type is "def [T] (T`1) -> builtins.int"
 [builtins fixtures/tuple.pyi]
+
+[case testNoGenericTypeVarTupleClassVarAccess]
+from typing import Generic, Tuple, TypeVarTuple, Unpack
+
+Ts = TypeVarTuple("Ts")
+class C(Generic[Unpack[Ts]]):
+    x: Tuple[Unpack[Ts]]
+
+reveal_type(C.x)  # E: Access to generic instance variables via class is ambiguous \
+                  # N: Revealed type is "builtins.tuple[Any, ...]"
+[builtins fixtures/tuple.pyi]

test-data/unit/semanal-classvar.test

@@ -207,14 +207,3 @@ class B:
         pass
 [out]
 main:4: error: ClassVar can only be used for assignments in class body
-
-[case testClassVarWithTypeVariable]
-from typing import ClassVar, TypeVar, Generic, List
-
-T = TypeVar('T')
-
-class Some(Generic[T]):
-    error: ClassVar[T]  # E: ClassVar cannot contain type variables
-    nested: ClassVar[List[List[T]]]  # E: ClassVar cannot contain type variables
-    ok: ClassVar[int]
-[out]