From f3b6759d38a5a3c7c829b2b7aeeb75ea25cf7317 Mon Sep 17 00:00:00 2001
From: Ethan Furman <ethan@stoneleaf.us>
Date: Tue, 8 Nov 2022 12:00:19 -0800
Subject: [PATCH] gh-99248: [Enum] fix negative number infinite loop (GH-99256)

[Enum] fix negative number infinite loop

- _iter_bits_lsb() now raises a ValueError if a negative number
  is passed in

- verify() now skips checking negative numbers for named flags
(cherry picked from commit 0b4ffb08ccdc21fc07ce90d3f78b58a25e1af653)

Co-authored-by: Ethan Furman <ethan@stoneleaf.us>
---
 Lib/enum.py                                      |  8 +++++++-
 Lib/test/test_enum.py                            | 16 +++++++++++++++-
 ...2022-11-08-11-15-37.gh-issue-99248.1vt8xI.rst |  1 +
 3 files changed, 23 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2022-11-08-11-15-37.gh-issue-99248.1vt8xI.rst

diff --git a/Lib/enum.py b/Lib/enum.py
index ec3ebde2868678..62d6e25cecce0f 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -114,9 +114,12 @@ def _break_on_call_reduce(self, proto):
         setattr(obj, '__module__', '<unknown>')
 
 def _iter_bits_lsb(num):
-    # num must be an integer
+    # num must be a positive integer
+    original = num
     if isinstance(num, Enum):
         num = num.value
+    if num < 0:
+        raise ValueError('%r is not a positive integer' % original)
     while num:
         b = num & (~num + 1)
         yield b
@@ -1856,6 +1859,9 @@ def __call__(self, enumeration):
                     if name in member_names:
                         # not an alias
                         continue
+                    if alias.value < 0:
+                        # negative numbers are not checked
+                        continue
                     values = list(_iter_bits_lsb(alias.value))
                     missed = [v for v in values if v not in member_values]
                     if missed:
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index d2b3a918d3ae01..a9b80ad0d3dbc3 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -14,7 +14,7 @@
 from enum import Enum, IntEnum, StrEnum, EnumType, Flag, IntFlag, unique, auto
 from enum import STRICT, CONFORM, EJECT, KEEP, _simple_enum, _test_simple_enum
 from enum import verify, UNIQUE, CONTINUOUS, NAMED_FLAGS, ReprEnum
-from enum import member, nonmember
+from enum import member, nonmember, _iter_bits_lsb
 from io import StringIO
 from pickle import dumps, loads, PicklingError, HIGHEST_PROTOCOL
 from test import support
@@ -174,6 +174,10 @@ def test_is_private(self):
         for name in self.sunder_names + self.dunder_names + self.random_names:
             self.assertFalse(enum._is_private('MyEnum', name), '%r is a private name?')
 
+    def test_iter_bits_lsb(self):
+        self.assertEqual(list(_iter_bits_lsb(7)), [1, 2, 4])
+        self.assertRaisesRegex(ValueError, '-8 is not a positive integer', list, _iter_bits_lsb(-8))
+
 
 # for subclassing tests
 
@@ -3965,6 +3969,16 @@ class Sillier(IntEnum):
             triple = 3
             value = 4
 
+    def test_negative_alias(self):
+        @verify(NAMED_FLAGS)
+        class Color(Flag):
+            RED = 1
+            GREEN = 2
+            BLUE = 4
+            WHITE = -1
+        # no error means success
+
+
 class TestInternals(unittest.TestCase):
 
     sunder_names = '_bad_', '_good_', '_what_ho_'
diff --git a/Misc/NEWS.d/next/Library/2022-11-08-11-15-37.gh-issue-99248.1vt8xI.rst b/Misc/NEWS.d/next/Library/2022-11-08-11-15-37.gh-issue-99248.1vt8xI.rst
new file mode 100644
index 00000000000000..99bf1d5d08ba26
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-11-08-11-15-37.gh-issue-99248.1vt8xI.rst
@@ -0,0 +1 @@
+fix negative numbers failing in verify()