Replace importlib_metadata with importlib.metadata on Python 3.8+

Fixes pytest-dev#222

changelog/222.trivial.rst

@@ -0,0 +1,2 @@
+Replace ``importlib_metadata`` backport with ``importlib.metadata`` from the
+standard library on Python 3.8+.

docs/conf.py

@@ -1,5 +1,8 @@
 # -*- coding: utf-8 -*-
-import importlib_metadata
+try:
+    from importlib import metadata
+except ImportError:
+    import importlib_metadata as metadata
 
 
 extensions = [
@@ -24,7 +27,7 @@
 copyright = u"2016, Holger Krekel"
 author = "Holger Krekel"
 
-release = importlib_metadata.version(project)
+release = metadata.version(project)
 # The short X.Y version.
 version = u".".join(release.split(".")[:2])
 

setup.py

@@ -37,7 +37,7 @@ def main():
         author_email="holger@merlinux.eu",
         url="https://github.com/pytest-dev/pluggy",
         python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*",
-        install_requires=["importlib-metadata>=0.12"],
+        install_requires=['importlib-metadata>=0.12;python_version<"3.8"'],
         extras_require={"dev": ["pre-commit", "tox"]},
         classifiers=classifiers,
         packages=["pluggy"],

src/pluggy/manager.py

@@ -3,7 +3,10 @@
 from .hooks import HookImpl, _HookRelay, _HookCaller, normalize_hookimpl_opts
 import warnings
 
-import importlib_metadata
+try:
+    from importlib import metadata
+except ImportError:
+    import importlib_metadata as metadata
 
 
 def _warn_for_function(warning, function):
@@ -279,7 +282,7 @@ def load_setuptools_entrypoints(self, group, name=None):
         :return: return the number of loaded plugins by this call.
         """
         count = 0
-        for dist in importlib_metadata.distributions():
+        for dist in metadata.distributions():
             for ep in dist.entry_points:
                 if (
                     ep.group != group

testing/test_pluginmanager.py

@@ -3,7 +3,12 @@
 """
 import pytest
 import types
-import importlib_metadata
+
+try:
+    from importlib import metadata
+except ImportError:
+    import importlib_metadata as metadata
+
 from pluggy import (
     PluginManager,
     PluginValidationError,
@@ -466,7 +471,7 @@ class Distribution(object):
     def my_distributions():
         return (dist,)
 
-    monkeypatch.setattr(importlib_metadata, "distributions", my_distributions)
+    monkeypatch.setattr(metadata, "distributions", my_distributions)
     num = pm.load_setuptools_entrypoints("hello")
     assert num == 1
     plugin = pm.get_plugin("myname")