Pass Distribution object back from subprocess

Upstream change removes the need for much of our workaround: pypa/setuptools#1890
I do not remove turning the object into a dict, as it would change the public signature of `get_setup_information`.

colcon_python_setup_py/package_identification/python_setup_py.py

@@ -277,25 +277,6 @@ def _get_setup_information(setup_py, *, env=None):
         'dist = run_setup('
         "    'setup.py', script_args=('--dry-run',), stop_after='config')",
 
-        "skip_keys = ('cmdclass', 'distclass', 'ext_modules', 'metadata')",
-        'data = {'
-        '    key: value for key, value in dist.__dict__.items() '
-        '    if ('
-        # skip private properties
-        "        not key.startswith('_') and "
-        # skip methods
-        '        not callable(value) and '
-        # skip objects whose representation can't be evaluated
-        '        key not in skip_keys and '
-        # skip display options since they have no value, using metadata instead
-        '        key not in dist.display_option_names'
-        '    )'
-        '}',
-        "data['metadata'] = {"
-        '    k: v for k, v in dist.metadata.__dict__.items() '
-        # skip values with custom type OrderedSet
-        "    if k not in ('license_files', 'provides_extras')}",
-
         'pickle.dump(data, sys.stdout.buffer)']
 
     # invoke distutils.core.run_setup() in a separate interpreter
@@ -305,5 +286,9 @@ def _get_setup_information(setup_py, *, env=None):
         cmd, stdout=subprocess.PIPE,
         cwd=os.path.abspath(str(setup_py.parent)), check=True, env=env)
     output = result.stdout
+    dist = pickle.loads(output)
 
-    return pickle.loads(output)
+    # turn into a dict for backwards compatibility
+    dist_dict = dist.__dict__.copy()
+    dist_dict['metadata'] = dist.metadata.__dict__
+    return dist_dict

setup.cfg

@@ -27,7 +27,8 @@ keywords = colcon
 [options]
 install_requires =
   colcon-core>=0.3.10
-  setuptools
+  # DistributionMetadata not picklable in these versions https://github.com/pypa/setuptools/issues/1888
+  setuptools !=42.*,!=43.*,!=44.*,!=45.*
 packages = find:
 tests_require =
   flake8>=3.6.0

test/spell_check.words

@@ -1,7 +1,6 @@
 apache
 chdir
 colcon
-distclass
 hashable
 iterdir
 lstrip