Bug 1473498 - [mozbuild.mozconfig] Improve error message in MozconfigLoadException r=glandium

Without the output, this exception wasn't being very helpful.

Differential Revision: https://phabricator.services.mozilla.com/D42015

--HG--
extra : moz-landing-system : lando

python/mozbuild/mozbuild/base.py

@@ -880,16 +880,7 @@ class MachCommandBase(MozbuildObject):
             sys.exit(1)
 
         except MozconfigLoadException as e:
-            print('Error loading mozconfig: ' + e.path)
-            print('')
             print(e.message)
-            if e.output:
-                print('')
-                print('mozconfig output:')
-                print('')
-                for line in e.output:
-                    print(line)
-
             sys.exit(1)
 
         MozbuildObject.__init__(self, topsrcdir, context.settings,
@@ -908,16 +899,7 @@ class MachCommandBase(MozbuildObject):
             sys.exit(1)
 
         except MozconfigLoadException as e:
-            print('Error loading mozconfig: ' + e.path)
-            print('')
             print(e.message)
-            if e.output:
-                print('')
-                print('mozconfig output:')
-                print('')
-                for line in e.output:
-                    print(line)
-
             sys.exit(1)
 
         # Always keep a log of the last command, but don't do that for mach

python/mozbuild/mozbuild/mozconfig.py

@@ -10,6 +10,7 @@ import re
 import sys
 import subprocess
 import traceback
+from textwrap import dedent
 
 from mozpack import path as mozpath
 from mozbuild.util import system_encoding
@@ -54,6 +55,20 @@ class MozconfigLoadException(Exception):
     def __init__(self, path, message, output=None):
         self.path = path
         self.output = output
+
+        message = dedent("""
+        Error loading mozconfig: {path}
+
+        {message}
+        """).format(path=self.path, message=message).lstrip()
+
+        if self.output:
+            message += dedent("""
+            mozconfig output:
+
+            {output}
+            """).format(output="\n".join(self.output))
+
         Exception.__init__(self, message)
 
 

python/mozbuild/mozbuild/test/test_mozconfig.py

@@ -455,8 +455,8 @@ class TestMozconfigLoader(unittest.TestCase):
             with self.assertRaises(MozconfigLoadException) as e:
                 self.get_loader().read_mozconfig(mozconfig.name)
 
-            self.assertTrue(e.exception.message.startswith(
-                'Evaluation of your mozconfig exited with an error'))
+            self.assertIn('Evaluation of your mozconfig exited with an error',
+                          e.exception.message)
             self.assertEquals(e.exception.path,
                               mozconfig.name.replace(os.sep, '/'))
             self.assertEquals(e.exception.output, ['hello world'])