Support charms providing templates with same basename

Replicate functionaltiy of ``charmhelpers.contrib.openstack``
where template files named after the absolute path of target
with path separators repalced by underscores can be used.

This convention is useful when charm author need to provide
templates with ambiguous basename.

Change-Id: I534fe52f38df7d1e409246115836223e90f080bc
Closes-Bug: #1872689

charms_openstack/charm/core.py

@@ -794,16 +794,25 @@ class BaseOpenStackCharmActions(object):
                     # means we need to skip this config to avoid rendering
                     return
 
-                charmhelpers.core.templating.render(
+                def _render(source):
-                    source=os.path.basename(conf),
+                    charmhelpers.core.templating.render(
-                    template_loader=os_templating.get_loader(
+                        source=source,
-                        'templates/', self.release),
+                        template_loader=os_templating.get_loader(
-                    target=conf,
+                            'templates/', self.release),
-                    context=adapters_instance,
+                        target=conf,
-                    config_template=config_template,
+                        context=adapters_instance,
-                    group=self.group,
+                        config_template=config_template,
-                    perms=self.permission_override_map.get(conf) or 0o640,
+                        group=self.group,
-                )
+                        perms=self.permission_override_map.get(conf) or 0o640,
+                    )
+                try:
+                    _render(os.path.basename(conf))
+                except LookupError:
+                    # if no template is found try looking for files named after
+                    # the absolute path of target with path separators replaced
+                    # by underscores.  This convention is useful when charm
+                    # author need to provide templates with ambiguous basenames
+                    _render('_'.join(conf.split(os.path.sep))[1:])
 
     def render_with_interfaces(self, interfaces, configs=None):
         """Render the configs using the interfaces passed; overrides any

unit_tests/charms_openstack/charm/test_core.py

@@ -519,6 +519,35 @@ class TestMyOpenStackCharm(BaseOpenStackCharmTest):
         assert isinstance(context, MyAdapter)
         self.assertEqual(context.interfaces, ['interface1', 'interface2'])
 
+        # test source template provided with filename that represents absoulute
+        # path of target config where path separators has been replaced by
+        # underscores
+        self.render.reset_mock()
+        self.render.side_effect = [LookupError, None]
+        self.target.render_configs(
+            ['/etc/some/path1'],
+            adapters_instance=self.target.adapters_instance)
+        self.render.assert_has_calls([
+            mock.call(
+                source='path1',
+                template_loader='my-loader',
+                target='/etc/some/path1',
+                context=mock.ANY,
+                config_template=None,
+                group='root',
+                perms=0o640,
+            ),
+            mock.call(
+                source='etc_some_path1',
+                template_loader='my-loader',
+                target='/etc/some/path1',
+                context=mock.ANY,
+                config_template=None,
+                group='root',
+                perms=0o640,
+            ),
+        ])
+
     def test_render_configs_construct_adapters_instance(self):
         # give us a way to check that the context manager was called.
         from contextlib import contextmanager