gh-139398: Make dir(Enum) include public _sunder_ helpers for REPL completions

Lib/enum.py

@@ -773,22 +773,31 @@ def __delattr__(cls, attr):
         super().__delattr__(attr)
 
     def __dir__(cls):
-        interesting = set([
-                '__class__', '__contains__', '__doc__', '__getitem__',
-                '__iter__', '__len__', '__members__', '__module__',
-                '__name__', '__qualname__',
-                ]
-                + cls._member_names_
-                )
-        if cls._new_member_ is not object.__new__:
-            interesting.add('__new__')
-        if cls.__init_subclass__ is not object.__init_subclass__:
-            interesting.add('__init_subclass__')
-        if cls._member_type_ is object:
-            return sorted(interesting)
-        else:
-            # return whatever mixed-in data type has
-            return sorted(set(dir(cls._member_type_)) | interesting)
+    interesting = set([
+        '__class__', '__contains__', '__doc__', '__getitem__',
+        '__iter__', '__len__', '__members__', '__module__',
+        '__name__', '__qualname__',
+    ] + cls._member_names_)
+
+    if cls._new_member_ is not object.__new__:
+        interesting.add('__new__')
+    if cls.__init_subclass__ is not object.__init_subclass__:
+        interesting.add('__init_subclass__')
+
+    # SGP: Include documented public _sunder_ helpers defined on the Enum class.
+    # SGP: This makes them discoverable via dir(Enum) so rlcompleter can surface
+    # SGP: them in REPL completions. (rlcompleter drives dotted-name completion
+    # SGP: from dir(); _add_alias_/_add_value_alias_ are supported _sunder_ APIs.)
+    for _n in ("_add_alias_", "_add_value_alias_"):
+        if _n in cls.__dict__:
+            interesting.add(_n)
+
+    if cls._member_type_ is object:
+        return sorted(interesting)
+    else:
+        # return whatever mixed-in data type has
+        # SGP: union the mixin's dir() with 'interesting'
+        return sorted(set(dir(cls._member_type_)) | interesting)
 
     def __getitem__(cls, name):
         """

Misc/NEWS.d/next/Library/2025-09-29-14-39-34.gh-issue-139398.tbFBKV.rst

@@ -0,0 +1 @@
+dir(Enum) now includes public _sunder_ helpers (_add_alias_, _add_value_alias_) for better REPL completion. (gh-139398)