Fix crash on dataclass field assigned a functional namedtuple() call

mypy/plugins/dataclasses.py

@@ -599,6 +599,10 @@ def collect_attributes(self) -> list[DataclassAttribute] | None:
                 # This might be a property / field name clash.
                 # We will issue an error later.
                 continue
+            if isinstance(node, TypeInfo):
+                # The declared type is shadowed by a class created from a call like
+                # `x: Foo = namedtuple('Foo', [...])`, so there is no dataclass field here.
+                continue
 
             assert isinstance(node, Var), node
 

test-data/unit/check-dataclasses.test

@@ -2746,6 +2746,19 @@ class B2(B1):  # E: A NamedTuple cannot be a dataclass
 
 [builtins fixtures/tuple.pyi]
 
+[case testNoCrashForDataclassFieldAssignedFunctionalNamedTuple]
+from collections import namedtuple
+from dataclasses import dataclass
+
+@dataclass
+class C:
+    p: "Point" = namedtuple("Point", ["x", "y"])  # E: First argument to namedtuple() should be "p", not "Point"
+
+@dataclass
+class D:
+    Point: "Point" = namedtuple("Point", ["x", "y"])
+[builtins fixtures/tuple.pyi]
+
 [case testDataclassesTypeGuard]
 import dataclasses