fix(dataclasses): skip non-Var ClassVars

mypy/plugins/dataclasses.py

@@ -600,7 +600,11 @@ def collect_attributes(self) -> list[DataclassAttribute] | None:
                 # We will issue an error later.
                 continue
 
-            assert isinstance(node, Var), node
+            # A ClassVar assigned a class definition, such as a TypedDict,
+            # can be represented by a TypeInfo rather than a Var. Dataclasses
+            # ignore ClassVars, so there is no attribute to collect here.
+            if not isinstance(node, Var):
+                continue
 
             # x: ClassVar[int] is ignored by dataclasses.
             if node.is_classvar:

test-data/unit/check-dataclasses.test

@@ -1,3 +1,17 @@
+[case testClassVarTypedDict]
+import dataclasses
+from typing import ClassVar, TypedDict
+
+@dataclasses.dataclass
+class X:
+    value: int
+    TD: ClassVar = TypedDict("TD", {"value": int})
+
+X.TD
+
+[builtins fixtures/tuple.pyi]
+[typing fixtures/typing-medium.pyi]
+
 [case testDataclassesBasic]
 from dataclasses import dataclass