MNT: remove a private helper class

- The definition of `__hash__` was doing nothing
- having a copy of a 1 line function in two sub-classes is simpler than having
  doing inheritance
- fixes an issues with mypy failing on an Enum class with no entries

Author: tacaswell

lib/matplotlib/_enums.py

@@ -14,17 +14,11 @@
 from matplotlib import _docstring
 
 
-class _AutoStringNameEnum(Enum):
+class __AutoStringNameEnum(Enum):
     """Automate the ``name = 'name'`` part of making a (str, Enum)."""
 
-    def _generate_next_value_(name, start, count, last_values):
-        return name
-
-    def __hash__(self):
-        return str(self).__hash__()
 
-
-class JoinStyle(str, _AutoStringNameEnum):
+class JoinStyle(str, Enum):
     """
     Define how the connection between two line segments is drawn.
 
@@ -79,6 +73,9 @@ class JoinStyle(str, _AutoStringNameEnum):
 
     """
 
+    def _generate_next_value_(name, start, count, last_values):
+        return name
+
     miter = auto()
     round = auto()
     bevel = auto()
@@ -116,7 +113,7 @@ def plot_angle(ax, x, y, angle, style):
         + "}"
 
 
-class CapStyle(str, _AutoStringNameEnum):
+class CapStyle(str, Enum):
     r"""
     Define how the two endpoints (caps) of an unclosed line are drawn.
 
@@ -151,6 +148,9 @@ class CapStyle(str, _AutoStringNameEnum):
         CapStyle.demo()
 
     """
+    def _generate_next_value_(name, start, count, last_values):
+        return name
+
     butt = auto()
     projecting = auto()
     round = auto()

lib/matplotlib/_enums.pyi

@@ -1,17 +1,16 @@
 from typing import cast
 from enum import Enum
 
-class _AutoStringNameEnum(Enum):
-    def __hash__(self) -> int: ...
 
-class JoinStyle(str, _AutoStringNameEnum):
+class JoinStyle(str, Enum):
     miter = cast(str, ...)
     round = cast(str, ...)
     bevel = cast(str, ...)
     @staticmethod
     def demo() -> None: ...
 
-class CapStyle(str, _AutoStringNameEnum):
+
+class CapStyle(str, Enum):
     butt = cast(str, ...)
     projecting = cast(str, ...)
     round = cast(str, ...)