Support provides_extra metadata

This was added to setuptools in [1] so we should support passing it
through from pbr.

Change-Id: I46493c18756bcb01c53575ab51ec5e5e97670fc3
1: b2ea3c4a20
Closes-Bug: 1760938

pbr/tests/test_util.py

@@ -160,3 +160,15 @@ class TestKeywordsParsingScenarios(base.BaseTestCase):
         kwargs = util.setup_cfg_to_setup_kwargs(config)
 
         self.assertEqual(self.expected_keywords, kwargs['keywords'])
+
+
+class TestProvidesExtras(base.BaseTestCase):
+    def test_provides_extras(self):
+        ini = """
+        [metadata]
+        provides_extras = foo
+                          bar
+        """
+        config = config_from_ini(ini)
+        kwargs = util.setup_cfg_to_setup_kwargs(config)
+        self.assertEqual(['foo', 'bar'], kwargs['provides_extras'])

pbr/util.py

@@ -113,6 +113,7 @@ D1_D2_SETUP_ARGS = {
     "setup_requires": ("metadata", "setup_requires_dist"),
     "python_requires": ("metadata",),
     "provides": ("metadata", "provides_dist"),  # **
+    "provides_extras": ("metadata",),
     "obsoletes": ("metadata", "obsoletes_dist"),  # **
     "package_dir": ("files", 'packages_root'),
     "packages": ("files",),
@@ -147,7 +148,8 @@ MULTI_FIELDS = ("classifiers",
                 "setup_requires",
                 "tests_require",
                 "keywords",
-                "cmdclass")
+                "cmdclass",
+                "provides_extras")
 
 # setup() arguments that can have mapping values in setup.cfg
 MAP_FIELDS = ("project_urls",)