Remove final use of pkg_resources

'pkg_resources' is slow, while 'importlib.metadata' is the new shiny and
is *much* faster. Recent version of 'importlib.metadata' - namely those
found in Python 3.10 or provided by the 4.4 'importlib-metadata'
backport - now provide the last bit of functionality we were missing to
remove 'pkg_resources' entirely, namely the ability to map package names
to modules. This is used for generating epilogs.

The benefits of this are huge, yielding a near 40% decrease in runtime
for the cliffdemo app (100mS after compared to 160mS) before.

Change-Id: I934d8a196d76622671781643f36bdb8a07d2f319
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

cliff/command.py

@@ -13,6 +13,7 @@
 import abc
 import inspect
 
+import importlib_metadata
 from stevedore import extension
 
 from cliff import _argparse
@@ -27,26 +28,15 @@ def _get_distributions_by_modules():
     distribution name (the name used with pip and PyPI) do not
     always match. We want to report which distribution caused the
     command to be installed, so we need to look up the values.
-
     """
-    import pkg_resources
     global _dists_by_mods
     if _dists_by_mods is None:
-        results = {}
-        for dist in pkg_resources.working_set:
-            try:
-                mod_names = dist.get_metadata('top_level.txt').strip()
-            except Exception:
-                # Could not retrieve metadata. Either the file is not
-                # present or we cannot read it. Ignore the
-                # distribution.
-                pass
-            else:
-                # Distributions may include multiple top-level
-                # packages (see setuptools for an example).
-                for mod_name in mod_names.splitlines():
-                    results[mod_name] = dist.project_name
-        _dists_by_mods = results
+        # There can be multiple distribution in the case of namespace packages
+        # so we'll just grab the first one
+        _dists_by_mods = {
+            k: v[0] for k, v in
+            importlib_metadata.packages_distributions().items()
+        }
     return _dists_by_mods
 
 

requirements.txt

@@ -1,4 +1,6 @@
 autopage>=0.4.0 # Apache 2.0
+# TODO: Drop this when Python 3.10 is our minimum supported version
+importlib_metadata>=4.4 # Apache-2.0
 cmd2>=1.0.0 # MIT
 PrettyTable>=0.7.2 # BSD
 stevedore>=2.0.1 # Apache-2.0