Special cases Enum and some special props to be non-final, refs python#11699 (python#11713)

Closes python#11699

Author: sobolevn

mypy/checker.py

@@ -50,6 +50,7 @@
     type_object_type,
     analyze_decorator_or_funcbase_access,
 )
+from mypy.semanal_enum import ENUM_BASES, ENUM_SPECIAL_PROPS
 from mypy.typeops import (
     map_type_from_supertype, bind_self, erase_to_bound, make_simplified_union,
     erase_def_to_union_or_bound, erase_to_union_or_bound, coerce_to_literal,
@@ -2522,13 +2523,14 @@ def check_compatibility_final_super(self, node: Var,
             self.msg.cant_override_final(node.name, base.name, node)
             return False
         if node.is_final:
+            if base.fullname in ENUM_BASES and node.name in ENUM_SPECIAL_PROPS:
+                return True
             self.check_if_final_var_override_writable(node.name, base_node, node)
         return True
 
     def check_if_final_var_override_writable(self,
                                              name: str,
-                                             base_node:
-                                             Optional[Node],
+                                             base_node: Optional[Node],
                                              ctx: Context) -> None:
         """Check that a final variable doesn't override writeable attribute.
 

mypy/checkexpr.py

@@ -14,6 +14,7 @@
     has_any_from_unimported_type, check_for_explicit_any, set_any_tvars, expand_type_alias,
     make_optional_type,
 )
+from mypy.semanal_enum import ENUM_BASES
 from mypy.types import (
     Type, AnyType, CallableType, Overloaded, NoneType, TypeVarType,
     TupleType, TypedDictType, Instance, ErasedType, UnionType,
@@ -1000,9 +1001,7 @@ def check_callable_call(self,
         ret_type = get_proper_type(callee.ret_type)
         if callee.is_type_obj() and isinstance(ret_type, Instance):
             callable_name = ret_type.type.fullname
-        if (isinstance(callable_node, RefExpr)
-            and callable_node.fullname in ('enum.Enum', 'enum.IntEnum',
-                                           'enum.Flag', 'enum.IntFlag')):
+        if isinstance(callable_node, RefExpr) and callable_node.fullname in ENUM_BASES:
             # An Enum() call that failed SemanticAnalyzerPass2.check_enum_call().
             return callee.ret_type, callee
 

mypy/plugins/enums.py

@@ -18,15 +18,13 @@
 from mypy.typeops import make_simplified_union
 from mypy.nodes import TypeInfo
 from mypy.subtypes import is_equivalent
+from mypy.semanal_enum import ENUM_BASES
 
-# Note: 'enum.EnumMeta' is deliberately excluded from this list. Classes that directly use
-# enum.EnumMeta do not necessarily automatically have the 'name' and 'value' attributes.
-ENUM_PREFIXES: Final = {"enum.Enum", "enum.IntEnum", "enum.Flag", "enum.IntFlag"}
-ENUM_NAME_ACCESS: Final = {"{}.name".format(prefix) for prefix in ENUM_PREFIXES} | {
-    "{}._name_".format(prefix) for prefix in ENUM_PREFIXES
+ENUM_NAME_ACCESS: Final = {"{}.name".format(prefix) for prefix in ENUM_BASES} | {
+    "{}._name_".format(prefix) for prefix in ENUM_BASES
 }
-ENUM_VALUE_ACCESS: Final = {"{}.value".format(prefix) for prefix in ENUM_PREFIXES} | {
-    "{}._value_".format(prefix) for prefix in ENUM_PREFIXES
+ENUM_VALUE_ACCESS: Final = {"{}.value".format(prefix) for prefix in ENUM_BASES} | {
+    "{}._value_".format(prefix) for prefix in ENUM_BASES
 }
 
 

mypy/semanal.py

@@ -116,7 +116,7 @@
 )
 from mypy.semanal_namedtuple import NamedTupleAnalyzer
 from mypy.semanal_typeddict import TypedDictAnalyzer
-from mypy.semanal_enum import EnumCallAnalyzer
+from mypy.semanal_enum import EnumCallAnalyzer, ENUM_BASES
 from mypy.semanal_newtype import NewTypeAnalyzer
 from mypy.reachability import (
     infer_reachability_of_if_statement, infer_condition_value, ALWAYS_FALSE, ALWAYS_TRUE,
@@ -1554,8 +1554,7 @@ def configure_base_classes(self,
                     self.fail('Cannot subclass "NewType"', defn)
                 if (
                     base.type.is_enum
-                    and base.type.fullname not in (
-                        'enum.Enum', 'enum.IntEnum', 'enum.Flag', 'enum.IntFlag')
+                    and base.type.fullname not in ENUM_BASES
                     and base.type.names
                     and any(not isinstance(n.node, (FuncBase, Decorator))
                             for n in base.type.names.values())

mypy/semanal_enum.py

@@ -4,6 +4,7 @@
 """
 
 from typing import List, Tuple, Optional, Union, cast
+from typing_extensions import Final
 
 from mypy.nodes import (
     Expression, Context, TypeInfo, AssignmentStmt, NameExpr, CallExpr, RefExpr, StrExpr,
@@ -13,6 +14,15 @@
 from mypy.semanal_shared import SemanticAnalyzerInterface
 from mypy.options import Options
 
+# Note: 'enum.EnumMeta' is deliberately excluded from this list. Classes that directly use
+# enum.EnumMeta do not necessarily automatically have the 'name' and 'value' attributes.
+ENUM_BASES: Final = frozenset((
+    'enum.Enum', 'enum.IntEnum', 'enum.Flag', 'enum.IntFlag',
+))
+ENUM_SPECIAL_PROPS: Final = frozenset((
+    'name', 'value', '_name_', '_value_', '_order_', '__order__',
+))
+
 
 class EnumCallAnalyzer:
     def __init__(self, options: Options, api: SemanticAnalyzerInterface) -> None:
@@ -62,7 +72,7 @@ class A(enum.Enum):
         if not isinstance(callee, RefExpr):
             return None
         fullname = callee.fullname
-        if fullname not in ('enum.Enum', 'enum.IntEnum', 'enum.Flag', 'enum.IntFlag'):
+        if fullname not in ENUM_BASES:
             return None
         items, values, ok = self.parse_enum_call_args(call, fullname.split('.')[-1])
         if not ok:

test-data/unit/check-enum.test

@@ -1392,7 +1392,7 @@ Medal.silver = 2  # E: Cannot assign to final attribute "silver"
 from enum import Enum
 class Types(Enum):
     key = 0
-    value = 1  # E: Cannot override writable attribute "value" with a final one
+    value = 1
 
 
 [case testEnumReusedKeys]
@@ -1677,3 +1677,28 @@ class A(Enum):
     class Inner: pass
 class B(A): pass  # E: Cannot inherit from final class "A"
 [builtins fixtures/bool.pyi]
+
+
+[case testEnumFinalSpecialProps]
+# https://github.com/python/mypy/issues/11699
+from enum import Enum, IntEnum
+
+class E(Enum):
+    name = 'a'
+    value = 'b'
+    _name_ = 'a1'
+    _value_ = 'b2'
+    _order_ = 'X Y'
+    __order__ = 'X Y'
+
+class EI(IntEnum):
+    name = 'a'
+    value = 1
+    _name_ = 'a1'
+    _value_ = 2
+    _order_ = 'X Y'
+    __order__ = 'X Y'
+
+E._order_ = 'a'  # E: Cannot assign to final attribute "_order_"
+EI.value = 2     # E: Cannot assign to final attribute "value"
+[builtins fixtures/bool.pyi]