Add support for BOM-signed env files

Signed-off-by: Joffrey F <joffrey@docker.com>

compose/config/environment.py

@@ -32,7 +32,7 @@ def env_vars_from_file(filename):
     elif not os.path.isfile(filename):
         raise ConfigurationError("%s is not a file." % (filename))
     env = {}
-    with contextlib.closing(codecs.open(filename, 'r', 'utf-8')) as fileobj:
+    with contextlib.closing(codecs.open(filename, 'r', 'utf-8-sig')) as fileobj:
         for line in fileobj:
             line = line.strip()
             if line and not line.startswith('#'):

tests/unit/config/environment_test.py

@@ -3,6 +3,11 @@ from __future__ import absolute_import
 from __future__ import print_function
 from __future__ import unicode_literals
 
+import codecs
+
+import pytest
+
+from compose.config.environment import env_vars_from_file
 from compose.config.environment import Environment
 from tests import unittest
 
@@ -38,3 +43,12 @@ class EnvironmentTest(unittest.TestCase):
         assert env.get_boolean('BAZ') is False
         assert env.get_boolean('FOOBAR') is True
         assert env.get_boolean('UNDEFINED') is False
+
+    def test_env_vars_from_file_bom(self):
+        tmpdir = pytest.ensuretemp('env_file')
+        self.addCleanup(tmpdir.remove)
+        with codecs.open('{}/bom.env'.format(str(tmpdir)), 'w', encoding='utf-8') as f:
+            f.write('\ufeffPARK_BOM=박봄\n')
+        assert env_vars_from_file(str(tmpdir.join('bom.env'))) == {
+            'PARK_BOM': '박봄'
+        }