[3.12] pythongh-104271: Fix auto() fallback in case of mixed type Enum (pythonGH-104279)

(cherry picked from commit f4e2049)

Co-authored-by: Itamar Ostricher <itamarost@gmail.com>
pythongh-104271: Fix auto() fallback in case of mixed type Enum

Author: itamaro

Lib/enum.py

@@ -1170,7 +1170,7 @@ def _generate_next_value_(name, start, count, last_values):
                     DeprecationWarning,
                     stacklevel=3,
                     )
-            for v in last_values:
+            for v in reversed(last_values):
                 try:
                     return v + 1
                 except TypeError:

Lib/test/test_enum.py

@@ -4176,11 +4176,14 @@ class Color(Enum):
                 red = 'red'
                 blue = 2
                 green = auto()
+                yellow = auto()
 
-        self.assertEqual(list(Color), [Color.red, Color.blue, Color.green])
+        self.assertEqual(list(Color),
+                         [Color.red, Color.blue, Color.green, Color.yellow])
         self.assertEqual(Color.red.value, 'red')
         self.assertEqual(Color.blue.value, 2)
         self.assertEqual(Color.green.value, 3)
+        self.assertEqual(Color.yellow.value, 4)
 
     @unittest.skipIf(
             python_version < (3, 13),