Update Flag masks in Python 3.11+ only, change stub reference

Also incorporates the change to `enum.Flag` and verbose names for enum
members in the stub.

src/nb_enum.cpp

@@ -119,7 +119,8 @@ void enum_append(PyObject *tp_, const char *name_, int64_t value_,
         fail("refusing to add duplicate key \"%s\" to enumeration \"%s\"!",
              name_, type_name(tp).c_str());
 
-    // handle updates of the flag and bit masks by hand,
+    # if PY_VERSION_HEX >= 0x030B0000
+    // In Python 3.11+, update the flag and bit masks by hand,
     // since enum._proto_member.__set_name__ is not called in this code path.
     if (t->flags & (uint32_t) enum_flags::flag_enum) {
         int64_t flag_mask = cast<int64_t>(tp.attr("_flag_mask_"));
@@ -133,6 +134,7 @@ void enum_append(PyObject *tp_, const char *name_, int64_t value_,
         int64_t bit_length = cast<int64_t>(tp.attr("_flag_mask_").attr("bit_length")());
         tp.attr("_all_bits_") = int_((2 << bit_length) - 1);
     }
+    #endif
 
     object el;
     if (issubclass(tp, val_tp))

tests/test_enum.py

@@ -1,5 +1,4 @@
 import test_enum_ext as t
-import enum
 import pytest
 
 def test01_unsigned_enum():
@@ -144,7 +143,9 @@ def test06_enum_flag():
     assert (t.Flag(3) ==  (t.Flag.A | t.Flag.B))
 
     # ensure the flag mask is set correctly by enum_append
-    assert t.Flag._flag_mask_ == 7
+    # in Python 3.11+
+    if hasattr(t.Flag, "_flag_mask_"):
+        assert t.Flag._flag_mask_ == 7
     assert (t.from_enum(t.Flag.A | t.Flag.C) == 5)
     assert (t.from_enum_implicit(t.Flag(1) | t.Flag(4)) == 5)
 

tests/test_enum_ext.pyi.ref

@@ -2,11 +2,11 @@ import enum
 from typing import overload
 
 
-A: Flag = 1
+A: Flag = Flag.A
 
-B: Flag = 2
+B: Flag = Flag.B
 
-C: Flag = 4
+C: Flag = Flag.C
 
 class ClassicEnum(enum.Enum):
     Item1 = 0
@@ -41,14 +41,9 @@ class EnumProperty:
     @property
     def read_enum(self) -> Enum: ...
 
-class Flag(enum.IntFlag):
+class Flag(enum.Flag):
     """enum-level docstring"""
 
-    __str__ = __repr__
-
-    def __repr__(self, /):
-        """Return repr(self)."""
-
     A = 1
     """Value A"""