Enums with annotations and no values are fine to be subclassed (#11579)

Closes #11578. Closes #11702.

Author: sobolevn

Diff for: mypy/nodes.py

@@ -840,6 +840,7 @@ def deserialize(cls, data: JsonDict) -> 'Decorator':
     'is_classmethod', 'is_property', 'is_settable_property', 'is_suppressed_import',
     'is_classvar', 'is_abstract_var', 'is_final', 'final_unset_in_class', 'final_set_in_init',
     'explicit_self_type', 'is_ready', 'from_module_getattr',
+    'has_explicit_value',
 ]
 
 
@@ -870,6 +871,7 @@ class Var(SymbolNode):
                  'is_suppressed_import',
                  'explicit_self_type',
                  'from_module_getattr',
+                 'has_explicit_value',
                  )
 
     def __init__(self, name: str, type: 'Optional[mypy.types.Type]' = None) -> None:
@@ -914,6 +916,9 @@ def __init__(self, name: str, type: 'Optional[mypy.types.Type]' = None) -> None:
         self.explicit_self_type = False
         # If True, this is an implicit Var created due to module-level __getattr__.
         self.from_module_getattr = False
+        # Var can be created with an explicit value `a = 1` or without one `a: int`,
+        # we need a way to tell which one is which.
+        self.has_explicit_value = False
 
     @property
     def name(self) -> str:

Diff for: mypy/semanal.py

@@ -1552,17 +1552,12 @@ def configure_base_classes(self,
             elif isinstance(base, Instance):
                 if base.type.is_newtype:
                     self.fail('Cannot subclass "NewType"', defn)
-                if (
-                    base.type.is_enum
-                    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())
-                ):
+                if self.enum_has_final_values(base):
                     # This means that are trying to subclass a non-default
                     # Enum class, with defined members. This is not possible.
                     # In runtime, it will raise. We need to mark this type as final.
                     # However, methods can be defined on a type: only values can't.
+                    # We also don't count values with annotations only.
                     base.type.is_final = True
                 base_types.append(base)
             elif isinstance(base, AnyType):
@@ -1601,6 +1596,25 @@ def configure_base_classes(self,
             return
         self.calculate_class_mro(defn, self.object_type)
 
+    def enum_has_final_values(self, base: Instance) -> bool:
+        if (
+            base.type.is_enum
+            and base.type.fullname not in ENUM_BASES
+            and base.type.names
+            and base.type.defn
+        ):
+            for sym in base.type.names.values():
+                if isinstance(sym.node, (FuncBase, Decorator)):
+                    continue  # A method
+                if not isinstance(sym.node, Var):
+                    return True  # Can be a class
+                if self.is_stub_file or sym.node.has_explicit_value:
+                    # Corner case: assignments like `x: int` are fine in `.py` files.
+                    # But, not is `.pyi` files, because we don't know
+                    # if there's aactually a value or not.
+                    return True
+        return False
+
     def configure_tuple_base_class(self,
                                    defn: ClassDef,
                                    base: TupleType,
@@ -2040,7 +2054,7 @@ def visit_import_all(self, i: ImportAll) -> None:
 
     def visit_assignment_expr(self, s: AssignmentExpr) -> None:
         s.value.accept(self)
-        self.analyze_lvalue(s.target, escape_comprehensions=True)
+        self.analyze_lvalue(s.target, escape_comprehensions=True, has_explicit_value=True)
 
     def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
         self.statement = s
@@ -2333,10 +2347,20 @@ def analyze_lvalues(self, s: AssignmentStmt) -> None:
             assert isinstance(s.unanalyzed_type, UnboundType)
             if not s.unanalyzed_type.args:
                 explicit = False
+
+        if s.rvalue:
+            if isinstance(s.rvalue, TempNode):
+                has_explicit_value = not s.rvalue.no_rhs
+            else:
+                has_explicit_value = True
+        else:
+            has_explicit_value = False
+
         for lval in s.lvalues:
             self.analyze_lvalue(lval,
                                 explicit_type=explicit,
-                                is_final=s.is_final_def)
+                                is_final=s.is_final_def,
+                                has_explicit_value=has_explicit_value)
 
     def apply_dynamic_class_hook(self, s: AssignmentStmt) -> None:
         if not isinstance(s.rvalue, CallExpr):
@@ -2776,7 +2800,8 @@ def analyze_lvalue(self,
                        nested: bool = False,
                        explicit_type: bool = False,
                        is_final: bool = False,
-                       escape_comprehensions: bool = False) -> None:
+                       escape_comprehensions: bool = False,
+                       has_explicit_value: bool = False) -> None:
         """Analyze an lvalue or assignment target.
 
         Args:
@@ -2790,7 +2815,11 @@ def analyze_lvalue(self,
         if escape_comprehensions:
             assert isinstance(lval, NameExpr), "assignment expression target must be NameExpr"
         if isinstance(lval, NameExpr):
-            self.analyze_name_lvalue(lval, explicit_type, is_final, escape_comprehensions)
+            self.analyze_name_lvalue(
+                lval, explicit_type, is_final,
+                escape_comprehensions,
+                has_explicit_value=has_explicit_value,
+            )
         elif isinstance(lval, MemberExpr):
             self.analyze_member_lvalue(lval, explicit_type, is_final)
             if explicit_type and not self.is_self_member_ref(lval):
@@ -2814,7 +2843,8 @@ def analyze_name_lvalue(self,
                             lvalue: NameExpr,
                             explicit_type: bool,
                             is_final: bool,
-                            escape_comprehensions: bool) -> None:
+                            escape_comprehensions: bool,
+                            has_explicit_value: bool) -> None:
         """Analyze an lvalue that targets a name expression.
 
         Arguments are similar to "analyze_lvalue".
@@ -2844,7 +2874,7 @@ def analyze_name_lvalue(self,
 
         if (not existing or isinstance(existing.node, PlaceholderNode)) and not outer:
             # Define new variable.
-            var = self.make_name_lvalue_var(lvalue, kind, not explicit_type)
+            var = self.make_name_lvalue_var(lvalue, kind, not explicit_type, has_explicit_value)
             added = self.add_symbol(name, var, lvalue, escape_comprehensions=escape_comprehensions)
             # Only bind expression if we successfully added name to symbol table.
             if added:
@@ -2895,7 +2925,9 @@ def is_alias_for_final_name(self, name: str) -> bool:
             existing = self.globals.get(orig_name)
             return existing is not None and is_final_node(existing.node)
 
-    def make_name_lvalue_var(self, lvalue: NameExpr, kind: int, inferred: bool) -> Var:
+    def make_name_lvalue_var(
+        self, lvalue: NameExpr, kind: int, inferred: bool, has_explicit_value: bool,
+    ) -> Var:
         """Return a Var node for an lvalue that is a name expression."""
         v = Var(lvalue.name)
         v.set_line(lvalue)
@@ -2910,6 +2942,7 @@ def make_name_lvalue_var(self, lvalue: NameExpr, kind: int, inferred: bool) -> V
             # fullanme should never stay None
             v._fullname = lvalue.name
         v.is_ready = False  # Type not inferred yet
+        v.has_explicit_value = has_explicit_value
         return v
 
     def make_name_lvalue_point_to_existing_def(
@@ -2953,7 +2986,14 @@ def analyze_tuple_or_list_lvalue(self, lval: TupleExpr,
             if len(star_exprs) == 1:
                 star_exprs[0].valid = True
             for i in items:
-                self.analyze_lvalue(i, nested=True, explicit_type=explicit_type)
+                self.analyze_lvalue(
+                    lval=i,
+                    nested=True,
+                    explicit_type=explicit_type,
+                    # Lists and tuples always have explicit values defined:
+                    # `a, b, c = value`
+                    has_explicit_value=True,
+                )
 
     def analyze_member_lvalue(self, lval: MemberExpr, explicit_type: bool, is_final: bool) -> None:
         """Analyze lvalue that is a member expression.

Diff for: test-data/unit/check-enum.test

@@ -1678,7 +1678,6 @@ class A(Enum):
 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
@@ -1702,3 +1701,48 @@ class EI(IntEnum):
 E._order_ = 'a'  # E: Cannot assign to final attribute "_order_"
 EI.value = 2     # E: Cannot assign to final attribute "value"
 [builtins fixtures/bool.pyi]
+
+[case testEnumNotFinalWithMethodsAndUninitializedValues]
+# https://github.com/python/mypy/issues/11578
+from enum import Enum
+from typing import Final
+
+class A(Enum):
+    x: int
+    def method(self) -> int: pass
+class B(A):
+    x = 1  # E: Cannot override writable attribute "x" with a final one
+
+class A1(Enum):
+    x: int = 1
+class B1(A1):  # E: Cannot inherit from final class "A1"
+    pass
+
+class A2(Enum):
+    x = 2
+class B2(A2):  # E: Cannot inherit from final class "A2"
+    pass
+
+# We leave this `Final` without a value,
+# because we need to test annotation only mode:
+class A3(Enum):
+    x: Final[int]  # type: ignore
+class B3(A3):
+    x = 1  # E: Cannot override final attribute "x" (previously declared in base class "A3")
+[builtins fixtures/bool.pyi]
+
+[case testEnumNotFinalWithMethodsAndUninitializedValuesStub]
+import lib
+
+[file lib.pyi]
+from enum import Enum
+class A(Enum):
+    x: int
+class B(A):  # E: Cannot inherit from final class "A"
+    x = 1    # E: Cannot override writable attribute "x" with a final one
+
+class C(Enum):
+    x = 1
+class D(C):  # E: Cannot inherit from final class "C"
+    x: int   # E: Cannot assign to final name "x"
+[builtins fixtures/bool.pyi]

Diff for: test-data/unit/check-incremental.test

@@ -5610,3 +5610,26 @@ class C:
     pass
 [rechecked]
 [stale]
+
+
+[case testEnumAreStillFinalAfterCache]
+import a
+class Ok(a.RegularEnum):
+    x = 1
+class NotOk(a.FinalEnum):
+    x = 1
+[file a.py]
+from enum import Enum
+class RegularEnum(Enum):
+    x: int
+class FinalEnum(Enum):
+    x = 1
+[builtins fixtures/isinstance.pyi]
+[out]
+main:3: error: Cannot override writable attribute "x" with a final one
+main:4: error: Cannot inherit from final class "FinalEnum"
+main:5: error: Cannot override final attribute "x" (previously declared in base class "FinalEnum")
+[out2]
+main:3: error: Cannot override writable attribute "x" with a final one
+main:4: error: Cannot inherit from final class "FinalEnum"
+main:5: error: Cannot override final attribute "x" (previously declared in base class "FinalEnum")