Fix attrs hashability detection when inheriting from mutable

Author: Tinche

mypy/plugins/attrs.py

@@ -371,7 +371,11 @@ def attr_class_maker_callback(
         _add_order(ctx, adder)
     if frozen:
         _make_frozen(ctx, attributes)
-    elif not hashable:
+        hashable = _get_decorator_bool_argument(
+            ctx, "hash", True
+        ) and _get_decorator_bool_argument(ctx, "unsafe_hash", True)
+
+    if not hashable:
         _remove_hashability(ctx)
 
     return True
@@ -836,6 +840,12 @@ def _make_frozen(ctx: mypy.plugin.ClassDefContext, attributes: list[Attribute])
             ctx.cls.info.names[var.name] = SymbolTableNode(MDEF, var)
             var.is_property = True
 
+    # Frozen classes are hashable by default, even if inheriting from non-frozen ones.
+    # We copy the `__hash__` signature from `object` to make them hashable.
+    # If the frozen class was created using `hash=False`, the hashability
+    # will be removed later.
+    ctx.cls.info.names["__hash__"] = ctx.cls.info.mro[-1].names["__hash__"]
+
 
 def _add_init(
     ctx: mypy.plugin.ClassDefContext,

test-data/unit/check-plugin-attrs.test

@@ -360,7 +360,8 @@ class A:
 
 a = A(5)
 a.a = 16  # E: Property "a" defined in "A" is read-only
-[builtins fixtures/bool.pyi]
+[builtins fixtures/plugin_attrs.pyi]
+
 [case testAttrsNextGenFrozen]
 from attr import frozen, field
 
@@ -370,7 +371,7 @@ class A:
 
 a = A(5)
 a.a = 16  # E: Property "a" defined in "A" is read-only
-[builtins fixtures/bool.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 
 [case testAttrsNextGenDetect]
 from attr import define, field
@@ -420,7 +421,7 @@ reveal_type(A)  # N: Revealed type is "def (a: builtins.int, b: builtins.bool) -
 reveal_type(B)  # N: Revealed type is "def (a: builtins.bool, b: builtins.int) -> __main__.B"
 reveal_type(C)  # N: Revealed type is "def (a: builtins.int) -> __main__.C"
 
-[builtins fixtures/bool.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 
 [case testAttrsDataClass]
 import attr
@@ -1155,7 +1156,7 @@ c = NonFrozenFrozen(1, 2)
 c.a = 17  # E: Property "a" defined in "NonFrozenFrozen" is read-only
 c.b = 17  # E: Property "b" defined in "NonFrozenFrozen" is read-only
 
-[builtins fixtures/bool.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 [case testAttrsCallableAttributes]
 from typing import Callable
 import attr
@@ -1178,7 +1179,7 @@ class G:
 class FFrozen(F):
     def bar(self) -> bool:
         return self._cb(5, 6)
-[builtins fixtures/callable.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 
 [case testAttrsWithFactory]
 from typing import List
@@ -1450,7 +1451,7 @@ class C:
     total = attr.ib(type=Bad)  # E: Name "Bad" is not defined
 
 C(0).total = 1  # E: Property "total" defined in "C" is read-only
-[builtins fixtures/bool.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 
 [case testTypeInAttrDeferredStar]
 import lib
@@ -1941,7 +1942,7 @@ class C:
         default=None, converter=default_if_none(factory=dict) \
         # E: Unsupported converter, only named functions, types and lambdas are currently supported
     )
-[builtins fixtures/dict.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 
 [case testAttrsUnannotatedConverter]
 import attr
@@ -2012,7 +2013,7 @@ class Sub(Base):
 
     @property
     def name(self) -> str: ...
-[builtins fixtures/property.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 
 [case testOverrideWithPropertyInFrozenClassChecked]
 from attrs import frozen
@@ -2035,7 +2036,7 @@ class Sub(Base):
 
 # This matches runtime semantics
 reveal_type(Sub)  # N: Revealed type is "def (*, name: builtins.str, first_name: builtins.str, last_name: builtins.str) -> __main__.Sub"
-[builtins fixtures/property.pyi]
+[builtins fixtures/plugin_attrs.pyi]
 
 [case testFinalInstanceAttribute]
 from attrs import define
@@ -2342,6 +2343,12 @@ class A:
 
 reveal_type(A.__hash__)  # N: Revealed type is "def (self: builtins.object) -> builtins.int"
 
+@frozen(hash=False)
+class B:
+    b: int
+
+reveal_type(B.__hash__)  # N: Revealed type is "None"
+
 [builtins fixtures/plugin_attrs.pyi]
 
 [case testManualHashHashability]
@@ -2380,3 +2387,18 @@ class B(A):
 reveal_type(B.__hash__)  # N: Revealed type is "None"
 
 [builtins fixtures/plugin_attrs.pyi]
+
+[case testSubclassingFrozenHashability]
+from attrs import define, frozen
+
+@define
+class A:
+    a: int
+
+@frozen
+class B(A):
+    pass
+
+reveal_type(B.__hash__)  # N: Revealed type is "def (self: builtins.object) -> builtins.int"
+
+[builtins fixtures/plugin_attrs.pyi]

test-data/unit/fixtures/plugin_attrs.pyi

@@ -35,3 +35,5 @@ class tuple(Sequence[Tco], Generic[Tco]):
     def __iter__(self) -> Iterator[Tco]: pass
     def __contains__(self, item: object) -> bool: pass
     def __getitem__(self, x: int) -> Tco: pass
+    
+property = object()  # Dummy definition