Give the user a better error message (without a stack trace) when there is a yaml error.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

compose/config/config.py

@@ -610,5 +610,6 @@ def load_yaml(filename):
     try:
         with open(filename, 'r') as fh:
             return yaml.safe_load(fh)
-    except IOError as e:
-        raise ConfigurationError(six.text_type(e))
+    except (IOError, yaml.YAMLError) as e:
+        error_name = getattr(e, '__module__', '') + '.' + e.__class__.__name__
+        raise ConfigurationError(u"{}: {}".format(error_name, e))

tests/unit/config/config_test.py

@@ -5,6 +5,7 @@ import shutil
 import tempfile
 from operator import itemgetter
 
+import py
 import pytest
 
 from compose.config import config
@@ -349,6 +350,18 @@ class ConfigTest(unittest.TestCase):
                 )
             )
 
+    def test_load_yaml_with_yaml_error(self):
+        tmpdir = py.test.ensuretemp('invalid_yaml_test')
+        invalid_yaml_file = tmpdir.join('docker-compose.yml')
+        invalid_yaml_file.write("""
+            web:
+              this is bogus: ok: what
+        """)
+        with pytest.raises(ConfigurationError) as exc:
+            config.load_yaml(str(invalid_yaml_file))
+
+        assert 'line 3, column 32' in exc.exconly()
+
 
 class InterpolationTest(unittest.TestCase):
     @mock.patch.dict(os.environ)