gh-82012: Deprecate bitwise inversion (~) of bool (#103487)

The bitwise inversion operator on bool returns the bitwise inversion of the
underlying int value; i.e. `~True == -2` such that `bool(~True) == True`.

It's a common pitfall that users mistake `~` as negation operator and actually
want `not`. Supporting `~` is an artifact of bool inheriting from int. Since there
is no real use-case for the current behavior, let's deprecate `~` on bool and
later raise an error. This removes a potential source errors for users.

Full reasoning: https://github.com/python/cpython/issues/82012#issuecomment-1258705971

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/Lib/test/test_bool.py b/Lib/test/test_bool.py
index 916e22a..34ecb45 100644
--- a/Lib/test/test_bool.py
+++ b/Lib/test/test_bool.py
@@ -58,8 +58,22 @@ class BoolTest(unittest.TestCase):
         self.assertEqual(-True, -1)
         self.assertEqual(abs(True), 1)
         self.assertIsNot(abs(True), True)
-        self.assertEqual(~False, -1)
-        self.assertEqual(~True, -2)
+        with self.assertWarns(DeprecationWarning):
+            # We need to put the bool in a variable, because the constant
+            # ~False is evaluated at compile time due to constant folding;
+            # consequently the DeprecationWarning would be issued during
+            # module loading and not during test execution.
+            false = False
+            self.assertEqual(~false, -1)
+        with self.assertWarns(DeprecationWarning):
+            # also check that the warning is issued in case of constant
+            # folding at compile time
+            self.assertEqual(eval("~False"), -1)
+        with self.assertWarns(DeprecationWarning):
+            true = True
+            self.assertEqual(~true, -2)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(eval("~True"), -2)
 
         self.assertEqual(False+2, 2)
         self.assertEqual(True+2, 3)