Retrieve sub property keys

The validation message was confusing by displaying only 1 level of
property of the service, even if the error was another level down.

Eg. if the 'files' property of 'extends' was the incorrect format,
it was displaying 'an invalid value for 'extends'', rather than
correctly retrieving 'files'.

Signed-off-by: Mazz Mosley <[email protected]>

compose/config/validation.py

@@ -99,12 +99,14 @@ def process_errors(errors):
                 if error.validator_value == "array":
                     msg = "an"
 
-                try:
-                    config_key = error.path[1]
-                    type_errors.append("Service '{}' has an invalid value for '{}', it should be {} {}".format(service_name, config_key, msg, error.validator_value))
-                except IndexError:
-                    config_key = error.path[0]
-                    root_msgs.append("Service '{}' doesn\'t have any configuration options. All top level keys in your docker-compose.yml must map to a dictionary of configuration options.'".format(config_key))
+                # pop the service name off our path
+                error.path.popleft()
+
+                if len(error.path) > 0:
+                    config_key = " ".join(["'%s'" % k for k in error.path])
+                    type_errors.append("Service '{}' configuration key {} contains an invalid type, it should be {} {}".format(service_name, config_key, msg, error.validator_value))
+                else:
+                    root_msgs.append("Service '{}' doesn\'t have any configuration options. All top level keys in your docker-compose.yml must map to a dictionary of configuration options.'".format(service_name))
             elif error.validator == 'required':
                 config_key = error.path[1]
                 required.append("Service '{}' option '{}' is invalid, {}".format(service_name, config_key, _clean_error_message(error.message)))

tests/unit/config_test.py

@@ -124,7 +124,7 @@ class ConfigTest(unittest.TestCase):
             )
 
     def test_invalid_config_type_should_be_an_array(self):
-        expected_error_msg = "Service 'foo' has an invalid value for 'links', it should be an array"
+        expected_error_msg = "Service 'foo' configuration key 'links' contains an invalid type, it should be an array"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
                 config.ConfigDetails(
@@ -690,6 +690,25 @@ class ExtendsTest(unittest.TestCase):
                 )
             )
 
+    def test_extends_validation_sub_property_key(self):
+        expected_error_msg = "Service 'web' configuration key 'extends' 'file' contains an invalid type"
+        with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
+            config.load(
+                config.ConfigDetails(
+                    {
+                        'web': {
+                            'image': 'busybox',
+                            'extends': {
+                                'file': 1,
+                                'service': 'web',
+                            }
+                        },
+                    },
+                    'tests/fixtures/extends',
+                    'filename.yml'
+                )
+            )
+
     def test_extends_validation_no_file_key_no_filename_set(self):
         dictionary = {'extends': {'service': 'web'}}