gh-96865: [Enum] fix Flag to use CONFORM boundary (GH-97528)

Author: ethanfurman

Lib/enum.py

@@ -1269,7 +1269,7 @@ class FlagBoundary(StrEnum):
 STRICT, CONFORM, EJECT, KEEP = FlagBoundary
 
 
-class Flag(Enum, boundary=STRICT):
+class Flag(Enum, boundary=CONFORM):
     """
     Support for flags
     """

Lib/test/test_enum.py

@@ -2927,7 +2927,7 @@ def test_bool(self):
             self.assertEqual(bool(f.value), bool(f))
 
     def test_boundary(self):
-        self.assertIs(enum.Flag._boundary_, STRICT)
+        self.assertIs(enum.Flag._boundary_, CONFORM)
         class Iron(Flag, boundary=STRICT):
             ONE = 1
             TWO = 2

Misc/NEWS.d/next/Library/2022-09-24-18-56-23.gh-issue-96865.o9WUkW.rst

@@ -0,0 +1,9 @@
+fix Flag to use boundary CONFORM
+
+This restores previous Flag behavior of allowing flags with non-sequential values to be combined; e.g.
+
+    class Skip(Flag):
+        TWO = 2
+        EIGHT = 8
+
+    Skip.TWO | Skip.EIGHT -> <Skip.TWO|EIGHT: 10>