avoid narrowing builtins

Author: hauntsaninja

mypy/checker.py

@@ -6545,6 +6545,9 @@ def comparison_type_narrowing_helper(self, node: ComparisonExpr) -> tuple[TypeMa
             if (
                 literal(expr) == LITERAL_TYPE
                 and not is_literal_none(expr)
+                and not is_literal_not_implemented(expr)
+                and not is_false_literal(expr)
+                and not is_true_literal(expr)
                 and not self.is_literal_enum(expr)
             ):
                 h = literal_hash(expr)
@@ -6584,7 +6587,7 @@ def comparison_type_narrowing_helper(self, node: ComparisonExpr) -> tuple[TypeMa
                     operands,
                     operand_types,
                     expr_indices,
-                    narrowable_operand_index_to_hash,
+                    narrowable_indices=narrowable_operand_index_to_hash.keys(),
                 )
             elif operator in {"in", "not in"}:
                 assert len(expr_indices) == 2
@@ -6649,7 +6652,7 @@ def equality_type_narrowing_helper(
         operands: list[Expression],
         operand_types: list[Type],
         expr_indices: list[int],
-        narrowable_operand_index_to_hash: dict[int, tuple[Key, ...]],
+        narrowable_indices: AbstractSet[int],
     ) -> tuple[TypeMap, TypeMap]:
         """Calculate type maps for '==', '!=', 'is' or 'is not' expression."""
         # If we haven't been able to narrow types yet, we might be dealing with a
@@ -6659,7 +6662,7 @@ def equality_type_narrowing_helper(
             operands,
             operand_types,
             expr_indices,
-            narrowable_operand_index_to_hash.keys(),
+            narrowable_indices=narrowable_indices,
         )
         if node is not None:
             type_if_map, type_else_map = self.find_type_equals_check(node, expr_indices)

test-data/unit/check-narrowing.test

@@ -2712,3 +2712,30 @@ reveal_type(t.foo)  # N: Revealed type is "__main__.D"
 t.foo = C1()
 reveal_type(t.foo)  # N: Revealed type is "__main__.C"
 [builtins fixtures/property.pyi]
+
+[case testNarrowingNotImplemented]
+from __future__ import annotations
+from typing_extensions import Self
+
+class X:
+    def __divmod__(self, other: Self | int) -> tuple[Self, Self]: ...
+
+    def __floordiv__(self, other: Self | int) -> Self:
+        qr = self.__divmod__(other)
+        if qr is NotImplemented:
+            return NotImplemented
+        return qr[0]
+[builtins fixtures/notimplemented.pyi]
+
+
+[case testNarrowingBooleans]
+# flags: --warn-return-any
+from typing import Any
+
+def foo(x: dict[str, Any]) -> bool:
+    if x.get("event") is False:
+        return False
+    if x.get("event") is True:
+        return True
+    raise
+[builtins fixtures/dict.pyi]

test-data/unit/fixtures/notimplemented.pyi

@@ -12,6 +12,7 @@ class str: pass
 class dict: pass
 class tuple: pass
 class ellipsis: pass
+class list: pass
 
 import sys