Fix handling of importlib.metadata for Python 3.8

poetry/repositories/installed_repository.py

-from importlib_metadata import distributions
 from poetry.packages import Package
 from poetry.utils._compat import Path
+from poetry.utils._compat import metadata
 from poetry.utils.env import Env
 
 from .repository import Repository
@@ -17,13 +17,12 @@ class InstalledRepository(Repository):
         repo = cls()
 
         for distribution in sorted(
-            distributions(path=env.sys_path), key=lambda d: str(d._path),
+            metadata.distributions(path=env.sys_path), key=lambda d: str(d._path),
         ):
-            metadata = distribution.metadata
-            name = metadata["name"]
-            version = metadata["version"]
+            name = distribution.metadata["name"]
+            version = distribution.metadata["version"]
             package = Package(name, version, version)
-            package.description = metadata.get("summary", "")
+            package.description = distribution.metadata.get("summary", "")
 
             repo.add_package(package)
 

poetry/utils/_compat.py

@@ -12,6 +12,13 @@ except ImportError:
     from glob import glob
 
 try:
+    from importlib import metadata
+    import zipfile as zipp
+except ImportError:
+    import importlib_metadata as metadata
+    import zipp
+
+try:
     import urllib.parse as urlparse
 except ImportError:
     import urlparse

tests/repositories/test_installed_repository.py

-import zipp
-
-from importlib_metadata import PathDistribution
 from poetry.repositories.installed_repository import InstalledRepository
 from poetry.utils._compat import Path
+from poetry.utils._compat import metadata
+from poetry.utils._compat import zipp
 from poetry.utils.env import MockEnv as BaseMockEnv
 
 
@@ -11,9 +10,11 @@ ENV_DIR = (FIXTURES_DIR / "installed").resolve()
 SITE_PACKAGES = ENV_DIR / "lib" / "python3.7" / "site-packages"
 SRC = ENV_DIR / "src"
 INSTALLED_RESULTS = [
-    PathDistribution(SITE_PACKAGES / "cleo-0.7.6.dist-info"),
-    PathDistribution(SRC / "pendulum" / "pendulum.egg-info"),
-    PathDistribution(zipp.Path(str(SITE_PACKAGES / "foo-0.1.0-py3.8.egg"), "EGG-INFO")),
+    metadata.PathDistribution(SITE_PACKAGES / "cleo-0.7.6.dist-info"),
+    metadata.PathDistribution(SRC / "pendulum" / "pendulum.egg-info"),
+    metadata.PathDistribution(
+        zipp.Path(str(SITE_PACKAGES / "foo-0.1.0-py3.8.egg"), "EGG-INFO")
+    ),
 ]
 
 
@@ -25,7 +26,8 @@ class MockEnv(BaseMockEnv):
 
 def test_load(mocker):
     mocker.patch(
-        "importlib_metadata.Distribution.discover", return_value=INSTALLED_RESULTS
+        "poetry.utils._compat.metadata.Distribution.discover",
+        return_value=INSTALLED_RESULTS,
     )
     mocker.patch(
         "poetry.vcs.git.Git.rev_parse",