migrate entrypoints handling to standard library importlib.metadata

We wrap a couple different versions of the stdlib interface, and fall
back to pkg_resources for compatibility with existing use cases on very
old versions of python.

For python 3.8 and on, we make sure to completely avoid external
dependencies, even backports.

Bug: PyFilesystem#577

Author: eli-schwartz

fs/opener/registry.py

@@ -8,7 +8,7 @@
 
 import collections
 import contextlib
-import pkg_resources
+import sys
 
 from ..errors import ResourceReadOnly
 from .base import Opener
@@ -21,6 +21,30 @@
     from ..base import FS
 
 
+if sys.version_info >= (3, 8):
+    import importlib.metadata
+
+    if sys.version_info >= (3, 10):
+
+        def entrypoints(group, name=None):
+            ep = importlib.metadata.entry_points(group=group, name=name)
+            return tuple(n for n in ep)
+
+    else:
+
+        def entrypoints(group, name=None):
+            ep = importlib.metadata.entry_points()
+            if name:
+                return tuple(n for n in ep.get(group, ()) if n.name == name)
+            return ep.get(group, ())
+
+else:
+    import pkg_resources
+
+    def entrypoints(group, name=None):
+        return tuple(pkg_resources.iter_entry_points(group, name))
+
+
 class Registry(object):
     """A registry for `Opener` instances."""
 
@@ -74,10 +98,7 @@ def protocols(self):
         """`list`: the list of supported protocols."""
         _protocols = list(self._protocols)
         if self.load_extern:
-            _protocols.extend(
-                entry_point.name
-                for entry_point in pkg_resources.iter_entry_points("fs.opener")
-            )
+            _protocols.extend(n.name for n in entrypoints("fs.opener"))
             _protocols = list(collections.OrderedDict.fromkeys(_protocols))
         return _protocols
 
@@ -101,10 +122,9 @@ def get_opener(self, protocol):
         """
         protocol = protocol or self.default_opener
 
-        if self.load_extern:
-            entry_point = next(
-                pkg_resources.iter_entry_points("fs.opener", protocol), None
-            )
+        ep = entrypoints("fs.opener", protocol)
+        if self.load_extern and ep:
+            entry_point = ep[0]
         else:
             entry_point = None
 

tests/test_opener.py

@@ -3,7 +3,6 @@
 import sys
 
 import os
-import pkg_resources
 import shutil
 import tempfile
 import unittest
@@ -21,6 +20,11 @@
 except ImportError:
     import mock
 
+if sys.version_info >= (3, 8):
+    import importlib.metadata
+else:
+    import pkg_resources
+
 
 class TestParse(unittest.TestCase):
     def test_registry_repr(self):
@@ -111,14 +115,25 @@ def test_protocols(self):
 
     def test_registry_protocols(self):
         # Check registry.protocols list the names of all available extension
-        extensions = [
-            pkg_resources.EntryPoint("proto1", "mod1"),
-            pkg_resources.EntryPoint("proto2", "mod2"),
-        ]
-        m = mock.MagicMock(return_value=extensions)
-        with mock.patch.object(
-            sys.modules["pkg_resources"], "iter_entry_points", new=m
-        ):
+        if sys.version_info >= (3, 8):
+            extensions = (
+                importlib.metadata.EntryPoint("proto1", "mod1", "fs.opener"),
+                importlib.metadata.EntryPoint("proto2", "mod2", "fs.opener"),
+            )
+            if sys.version_info >= (3, 10):
+                m = mock.MagicMock(return_value=extensions)
+            else:
+                m = mock.MagicMock(return_value={"fs.opener": extensions})
+            patch = mock.patch("importlib.metadata.entry_points", m)
+        else:
+            extensions = [
+                pkg_resources.EntryPoint("proto1", "mod1"),
+                pkg_resources.EntryPoint("proto2", "mod2"),
+            ]
+            m = mock.MagicMock(return_value=extensions)
+            patch = mock.patch("pkg_resources.iter_entry_points", m)
+
+        with patch:
             self.assertIn("proto1", opener.registry.protocols)
             self.assertIn("proto2", opener.registry.protocols)
 
@@ -129,11 +144,19 @@ def test_unknown_protocol(self):
     def test_entry_point_load_error(self):
 
         entry_point = mock.MagicMock()
+        entry_point.name = "test"
         entry_point.load.side_effect = ValueError("some error")
 
-        iter_entry_points = mock.MagicMock(return_value=iter([entry_point]))
-
-        with mock.patch("pkg_resources.iter_entry_points", iter_entry_points):
+        if sys.version_info >= (3, 8):
+            if sys.version_info >= (3, 10):
+                entry_points = mock.MagicMock(return_value=tuple([entry_point]))
+            else:
+                entry_points = mock.MagicMock(return_value={"fs.opener": [entry_point]})
+            patch = mock.patch("importlib.metadata.entry_points", entry_points)
+        else:
+            iter_entry_points = mock.MagicMock(return_value=iter([entry_point]))
+            patch = mock.patch("pkg_resources.iter_entry_points", iter_entry_points)
+        with patch:
             with self.assertRaises(errors.EntryPointError) as ctx:
                 opener.open_fs("test://")
             self.assertEqual(
@@ -145,10 +168,19 @@ class NotAnOpener(object):
             pass
 
         entry_point = mock.MagicMock()
+        entry_point.name = "test"
         entry_point.load = mock.MagicMock(return_value=NotAnOpener)
-        iter_entry_points = mock.MagicMock(return_value=iter([entry_point]))
 
-        with mock.patch("pkg_resources.iter_entry_points", iter_entry_points):
+        if sys.version_info >= (3, 8):
+            if sys.version_info >= (3, 10):
+                entry_points = mock.MagicMock(return_value=tuple([entry_point]))
+            else:
+                entry_points = mock.MagicMock(return_value={"fs.opener": [entry_point]})
+            patch = mock.patch("importlib.metadata.entry_points", entry_points)
+        else:
+            iter_entry_points = mock.MagicMock(return_value=iter([entry_point]))
+            patch = mock.patch("pkg_resources.iter_entry_points", iter_entry_points)
+        with patch:
             with self.assertRaises(errors.EntryPointError) as ctx:
                 opener.open_fs("test://")
             self.assertEqual("entry point did not return an opener", str(ctx.exception))
@@ -162,10 +194,20 @@ def open_fs(self, *args, **kwargs):
                 pass
 
         entry_point = mock.MagicMock()
+        entry_point.name = "test"
         entry_point.load = mock.MagicMock(return_value=BadOpener)
-        iter_entry_points = mock.MagicMock(return_value=iter([entry_point]))
 
-        with mock.patch("pkg_resources.iter_entry_points", iter_entry_points):
+        if sys.version_info >= (3, 8):
+            if sys.version_info >= (3, 10):
+                entry_points = mock.MagicMock(return_value=tuple([entry_point]))
+            else:
+                entry_points = mock.MagicMock(return_value={"fs.opener": [entry_point]})
+            patch = mock.patch("importlib.metadata.entry_points", entry_points)
+        else:
+            iter_entry_points = mock.MagicMock(return_value=iter([entry_point]))
+            patch = mock.patch("pkg_resources.iter_entry_points", iter_entry_points)
+
+        with patch:
             with self.assertRaises(errors.EntryPointError) as ctx:
                 opener.open_fs("test://")
             self.assertEqual(