Fix crash on invalid redefinition in dataclass

mypy/plugins/dataclasses.py

@@ -602,6 +602,13 @@ def collect_attributes(self) -> list[DataclassAttribute] | None:
 
             assert isinstance(node, Var), node
 
+            if node is not lhs.node:
+                # We create new Vars in _propertize_callables(), so it is OK.
+                if not isinstance(get_proper_type(node.type), CallableType):
+                    # There is an invalid redefinition. Avoid temptation to guess,
+                    # and skip both, see testDataclassVariableBadRedefine.
+                    continue
+
             # x: ClassVar[int] is ignored by dataclasses.
             if node.is_classvar:
                 continue

test-data/unit/check-dataclasses.test

@@ -670,6 +670,86 @@ reveal_type(x)  # N: Revealed type is "typing._SpecialForm"
 [builtins fixtures/dataclasses.pyi]
 [typing fixtures/typing-medium.pyi]
 
+[case testFunctionAliasDataclassNoCrash]
+from dataclasses import dataclass
+
+def fn(a: int) -> int:
+    return a
+
+@dataclass
+class Test:
+    foo = fn
+    foo: int = 42  # E: Name "foo" already defined on line 8
+
+reveal_type(Test.foo)  # N: Revealed type is "def (a: builtins.int) -> builtins.int"
+[builtins fixtures/dataclasses.pyi]
+[typing fixtures/typing-medium.pyi]
+
+[case testDataclassVariableBadRedefine]
+from dataclasses import dataclass
+
+@dataclass
+class Test:
+    foo = "test"
+    foo: int = 42  # E: Name "foo" already defined on line 5
+
+reveal_type(Test)  # N: Revealed type is "def () -> __main__.Test"
+reveal_type(Test.foo)  # N: Revealed type is "builtins.str"
+[builtins fixtures/dataclasses.pyi]
+[typing fixtures/typing-medium.pyi]
+
+[case testDataclassCallableAttrRegular]
+from dataclasses import dataclass
+from typing import Callable
+
+@dataclass
+class Defer(Parent):
+    b: int
+
+@dataclass
+class Parent:
+    key: Callable[[], str]
+    a: int
+
+reveal_type(Parent)  # N: Revealed type is "def (key: def () -> builtins.str, a: builtins.int) -> __main__.Parent"
+[builtins fixtures/dataclasses.pyi]
+[typing fixtures/typing-medium.pyi]
+
+[case testDataclassCallableAttrDefault]
+from dataclasses import dataclass
+from typing import Callable
+
+@dataclass
+class Defer(Parent):
+    b: int = 0
+
+@dataclass
+class Parent:
+    key: Callable[[], str] = lambda: "yes"
+    a: int = 0
+
+reveal_type(Parent)  # N: Revealed type is "def (key: def () -> builtins.str =, a: builtins.int =) -> __main__.Parent"
+reveal_type(Parent.key)  # N: Revealed type is "def () -> builtins.str"
+[builtins fixtures/dataclasses.pyi]
+[typing fixtures/typing-medium.pyi]
+
+[case testDataclassCallableAttrFrozen]
+from dataclasses import dataclass
+from typing import Callable
+
+@dataclass(frozen=True)
+class Defer(Parent):
+    b: int
+
+@dataclass(frozen=True)
+class Parent:
+    key: Callable[[], str]
+    a: int
+
+reveal_type(Parent)  # N: Revealed type is "def (key: def () -> builtins.str, a: builtins.int) -> __main__.Parent"
+[builtins fixtures/dataclasses.pyi]
+[typing fixtures/typing-medium.pyi]
+
 [case testDataclassOrdering]
 from dataclasses import dataclass
 
@@ -1702,6 +1782,34 @@ A(a=func).a()
 A(a=func).a = func  # E: Property "a" defined in "A" is read-only
 [builtins fixtures/dataclasses.pyi]
 
+[case testDataclassesCallableFrozenOverride]
+from dataclasses import dataclass
+from typing import Callable
+@dataclass(frozen=True)
+class A:
+    a: Callable[[int], str] = lambda x: "yes"
+
+def foo(x: int) -> str:
+    return "no"
+
+@dataclass(frozen=True)
+class Sub(A):
+    # This is no-op for attribute access on instances,
+    # so we effectively check the subtyping as if accessed on class.
+    a = foo
+[builtins fixtures/dataclasses.pyi]
+
+[case testDataclassesCallableFrozenSelf]
+from dataclasses import dataclass
+from typing import Self, Callable
+@dataclass(frozen=True)
+class A:
+    a: Callable[[Self], str]
+
+a: A
+reveal_type(a.a)  # N: Revealed type is "def (__main__.A) -> builtins.str"
+[builtins fixtures/dataclasses.pyi]
+
 [case testDataclassInFunctionDoesNotCrash]
 from dataclasses import dataclass