Bug 1600530 - Consider MOZ_OBJDIR from the environment when there is no mozconfig. r=nalexander

We currently only deal with MOZ_OBJDIR in the environment when there is
a mozconfig.

Differential Revision: https://phabricator.services.mozilla.com/D80308

python/mozbuild/mozbuild/mozconfig.py

@@ -111,6 +111,8 @@ class MozconfigLoader(object):
         }
 
         if path is None:
+            if 'MOZ_OBJDIR' in os.environ:
+                result['topobjdir'] = os.environ['MOZ_OBJDIR']
             return result
 
         path = mozpath.normsep(path)

python/mozbuild/mozbuild/test/test_mozconfig.py

@@ -113,6 +113,11 @@ class TestMozconfigLoader(unittest.TestCase):
             self.assertEqual(result['make_flags'], ['-j8', '-s'])
             self.assertEqual(result['make_extra'], ['FOO=BAR BAZ', 'BIZ=1'])
 
+    def test_read_no_mozconfig_objdir_environ(self):
+        os.environ['MOZ_OBJDIR'] = 'obj-firefox'
+        result = self.get_loader().read_mozconfig()
+        self.assertEqual(result['topobjdir'], 'obj-firefox')
+
     def test_read_empty_mozconfig_objdir_environ(self):
         os.environ['MOZ_OBJDIR'] = 'obj-firefox'
         with NamedTemporaryFile(mode='w') as mozconfig: