Fix crash in dataclass protocol with self attribute assignment

mypy/semanal.py

@@ -3647,7 +3647,7 @@ def analyze_lvalue(
  has_explicit_value=has_explicit_value,
  )
  elif isinstance(lval, MemberExpr):
- self.analyze_member_lvalue(lval, explicit_type, is_final)
+ self.analyze_member_lvalue(lval, explicit_type, is_final, has_explicit_value)
  if explicit_type and not self.is_self_member_ref(lval):
  self.fail("Type cannot be declared in assignment to non-self attribute", lval)
  elif isinstance(lval, IndexExpr):
@@ -3824,7 +3824,9 @@ def analyze_tuple_or_list_lvalue(self, lval: TupleExpr, explicit_type: bool = Fa
  has_explicit_value=True,
  )
 
- def analyze_member_lvalue(self, lval: MemberExpr, explicit_type: bool, is_final: bool) -> None:
+ def analyze_member_lvalue(
+ self, lval: MemberExpr, explicit_type: bool, is_final: bool, has_explicit_value: bool
+ ) -> None:
  """Analyze lvalue that is a member expression.
 
  Arguments:
@@ -3853,12 +3855,18 @@ def analyze_member_lvalue(self, lval: MemberExpr, explicit_type: bool, is_final:
  and explicit_type
  ):
  self.attribute_already_defined(lval.name, lval, cur_node)
- # If the attribute of self is not defined in superclasses, create a new Var, ...
+ if self.type.is_protocol and has_explicit_value and cur_node is not None:
+ # Make this variable non-abstract, it would be safer to do this only if we
+ # are inside __init__, but we do this always to preserve historical behaviour.
+ if isinstance(cur_node.node, Var):
+ cur_node.node.is_abstract_var = False
  if (
+ # If the attribute of self is not defined, create a new Var, ...
  node is None
- or (isinstance(node.node, Var) and node.node.is_abstract_var)
+ # ... or if it is defined as abstract in a *superclass*.
+ or (cur_node is None and isinstance(node.node, Var) and node.node.is_abstract_var)
  # ... also an explicit declaration on self also creates a new Var.
- # Note that `explicit_type` might has been erased for bare `Final`,
+ # Note that `explicit_type` might have been erased for bare `Final`,
  # so we also check if `is_final` is passed.
  or (cur_node is None and (explicit_type or is_final))
  ):

test-data/unit/check-dataclasses.test

@@ -2037,3 +2037,16 @@ Foo(
  present_5=5,
 )
 [builtins fixtures/dataclasses.pyi]
+
+[case testProtocolNoCrash]
+from typing import Protocol, Union, ClassVar
+from dataclasses import dataclass, field
+
+DEFAULT = 0
+
+@dataclass
+class Test(Protocol):
+ x: int
+ def reset(self) -> None:
+ self.x = DEFAULT
+[builtins fixtures/dataclasses.pyi]

test-data/unit/check-protocols.test

@@ -4054,3 +4054,14 @@ class P(Protocol):
 
 [file lib.py]
 class C: ...
+
+[case testAllowDefaultConstructorInProtocols]
+from typing import Protocol
+
+class P(Protocol):
+ x: int
+ def __init__(self, x: int) -> None:
+ self.x = x
+
+class C(P): ...
+C(0) # OK