Skip processing the node, avoid modifying the SymbolTable

Author: AlexWaygood

mypy/plugins/dataclasses.py

@@ -1,6 +1,6 @@
 """Plugin that provides support for dataclasses."""
 
-from typing import Dict, List, Set, Tuple, Optional, Union
+from typing import Dict, List, Set, Tuple, Optional
 from typing_extensions import Final
 
 from mypy.nodes import (
@@ -16,7 +16,7 @@
 from mypy.typeops import map_type_from_supertype
 from mypy.types import (
     Type, Instance, NoneType, TypeVarType, CallableType, TupleType, LiteralType,
-    get_proper_type, AnyType, TypeOfAny, TypeType,
+    get_proper_type, AnyType, TypeOfAny,
 )
 from mypy.server.trigger import make_wildcard_trigger
 from mypy.state import state
@@ -342,23 +342,10 @@ def collect_attributes(self) -> Optional[List[DataclassAttribute]]:
                     ),
                     node
                 )
-                # Now do our best to simulate the runtime,
-                # which treates a TypeAlias definition in a dataclass class
-                # as an instance field with a default value.
-                #
-                # Replace the `TypeAlias` node with a `Var` node, so that we do the same.
-                target, fullname = node.target, node.fullname
-                proper_target = get_proper_type(target)
-                var_type: Union[TypeType, AnyType]
-                if isinstance(proper_target, Instance):
-                    var_type = TypeType(proper_target, line=node.line, column=node.column)
-                # Something else -- fallback to Any
-                else:
-                    var_type = AnyType(TypeOfAny.from_error)
-                var = Var(name=node.name, type=var_type)
-                var.info = cls.info
-                var._fullname = fullname
-                sym.node = node = var
+                # Skip processing this node. This doesn't match the runtime behaviour,
+                # but the only alternative would be to modify the SymbolTable,
+                # and it's a little hairy to do that in a plugin.
+                continue
 
             assert isinstance(node, Var)
 

test-data/unit/check-dataclasses.test

@@ -528,19 +528,17 @@ class One:
     S: TypeAlias = Foo  # E: Type aliases inside dataclass definitions are not supported at runtime
 
 a = One()
-b = One(Foo)
-reveal_type(a.S)  # N: Revealed type is "Type[__main__.Foo]"
-reveal_type(b.S)  # N: Revealed type is "Type[__main__.Foo]"
+reveal_type(a.S)  # N: Revealed type is "def (x: builtins.int) -> __main__.Foo"
 a.S()  # E: Missing positional argument "x" in call to "Foo"
 reveal_type(a.S(5))  # N: Revealed type is "__main__.Foo"
-reveal_type(b.S(98))  # N: Revealed type is "__main__.Foo"
 
 @dataclass
 class Two:
     S: TypeAlias = Callable[[int], str]  # E: Type aliases inside dataclass definitions are not supported at runtime
 
 c = Two()
-reveal_type(c.S)  # N: Revealed type is "Any"
+x = c.S  # E: Member "S" is not assignable
+reveal_type(x)  # N: Revealed type is "Any"
 [builtins fixtures/dataclasses.pyi]
 
 [case testDataclassOrdering]