maybe fix

Author: JelleZijlstra

mypy/semanal.py

@@ -3360,8 +3360,6 @@ def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
         s.is_alias_def = False
 
         sentinel_definition = self.is_sentinel_declaration(s)
-        if sentinel_definition and self.is_existing_final_lvalue(s):
-            sentinel_definition = False
 
         # OK, this is a regular assignment, perform the necessary analysis steps.
         s.is_final_def = self.unwrap_final(s)
@@ -3399,15 +3397,6 @@ def is_sentinel_declaration(self, s: AssignmentStmt) -> bool:
             return False
         return True
 
-    def is_existing_final_lvalue(self, s: AssignmentStmt) -> bool:
-        if len(s.lvalues) != 1 or not isinstance(s.lvalues[0], NameExpr):
-            return False
-        name = s.lvalues[0].name
-        existing = self.current_symbol_table().get(name)
-        if existing is not None and is_final_node(existing.node):
-            return True
-        return self.is_alias_for_final_name(name)
-
     def setup_sentinel_var(self, s: AssignmentStmt) -> None:
         lvalue = s.lvalues[0]
         assert isinstance(lvalue, NameExpr)

mypy/test/testtypes.py

@@ -5,6 +5,9 @@
 import re
 from unittest import TestCase, skipUnless
 
+from librt.internal import ReadBuffer, WriteBuffer
+
+from mypy.cache import read_tag
 from mypy.erasetype import erase_type, remove_instance_last_known_values
 from mypy.indirection import TypeIndirectionVisitor
 from mypy.join import join_types
@@ -33,6 +36,7 @@
     AnyType,
     CallableType,
     Instance,
+    LITERAL_TYPE,
     LiteralType,
     NoneType,
     Overloaded,
@@ -75,6 +79,16 @@ def test_sentinel_literal_json_roundtrip(self) -> None:
         self.assertEqual(roundtrip.value, literal.value)
         self.assertEqual(roundtrip.fallback.type_ref, self.fx.a.type.fullname)
 
+    def test_sentinel_literal_ff_roundtrip(self) -> None:
+        literal = LiteralType(SentinelValue("__main__.MISSING", "MISSING"), self.fx.a)
+        data = WriteBuffer()
+        literal.write(data)
+        buffer = ReadBuffer(data.getvalue())
+        assert read_tag(buffer) == LITERAL_TYPE
+        roundtrip = LiteralType.read(buffer)
+        self.assertEqual(roundtrip.value, literal.value)
+        self.assertEqual(roundtrip.fallback.type_ref, self.fx.a.type.fullname)
+
     def test_simple_unbound_type(self) -> None:
         u = UnboundType("Foo")
         assert_equal(str(u), "Foo?")

mypy/types.py

@@ -3319,8 +3319,8 @@ def write(self, data: WriteBuffer) -> None:
         self.fallback.write(data)
         if isinstance(self.value, SentinelValue):
             write_tag(data, LITERAL_SENTINEL)
-            write_str(data, self.value.fullname)
-            write_str(data, self.value.name)
+            write_str_bare(data, self.value.fullname)
+            write_str_bare(data, self.value.name)
         else:
             write_literal(data, self.value)
         write_tag(data, END_TAG)
@@ -3331,7 +3331,7 @@ def read(cls, data: ReadBuffer) -> LiteralType:
         fallback = Instance.read(data)
         tag = read_tag(data)
         if tag == LITERAL_SENTINEL:
-            value = SentinelValue(read_str(data), read_str(data))
+            value = SentinelValue(read_str_bare(data), read_str_bare(data))
         else:
             value = read_literal(data, tag)
         ret = LiteralType(value, fallback)

test-data/unit/check-sentinels.test

@@ -69,7 +69,18 @@ def outer() -> None:
 from typing_extensions import Sentinel
 
 MISSING = Sentinel("MISSING")
-MISSING = Sentinel("OTHER")  # E: Cannot assign to final name "MISSING"
+MISSING = Sentinel("OTHER")  # E: Cannot redefine an existing name as final
+[builtins fixtures/tuple.pyi]
+
+[case testSentinelImplicitlyFinalWithLaterReference]
+from typing_extensions import Sentinel
+
+_SENTINEL = Sentinel("_SENTINEL")
+
+def func(x: int | _SENTINEL = _SENTINEL) -> int:
+    if x is _SENTINEL:
+        return 0
+    return x
 [builtins fixtures/tuple.pyi]
 
 [case testBuiltinsSentinelTypeExpression]