Rely on 'selectable' interface for entry points. (#2126)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/changelog/2093.misc.rst

@@ -0,0 +1 @@
+Plugins now use 'selectable' entry points.

setup.cfg

@@ -41,6 +41,7 @@ project_urls =
 packages = find:
 install_requires =
     appdirs>=1.4.3,<2
+    backports.entry_points_selectable>=1.0.4
     distlib>=0.3.1,<1
     filelock>=3.0.0,<4
     six>=1.9.0,<2   # keep it >=1.9.0 as it may cause problems on LTS platforms

src/virtualenv/run/plugin/base.py

@@ -1,12 +1,8 @@
 from __future__ import absolute_import, unicode_literals
 
-import sys
 from collections import OrderedDict
 
-if sys.version_info >= (3, 8):
-    from importlib.metadata import entry_points
-else:
-    from importlib_metadata import entry_points
+from backports.entry_points_selectable import entry_points
 
 
 class PluginLoader(object):
@@ -15,7 +11,7 @@ class PluginLoader(object):
 
     @classmethod
     def entry_points_for(cls, key):
-        return OrderedDict((e.name, e.load()) for e in cls.entry_points().get(key, {}))
+        return OrderedDict((e.name, e.load()) for e in cls.entry_points().select(group=key))
 
     @staticmethod
     def entry_points():