Bug 1446019 - Improve error message for LOCAL_INCLUDES pointing to topobjdir; r=froydnj

The old message is ambiguous as to why it failed. The new one tells
you why and hopefully gives you enough info to fix it.

MozReview-Commit-ID: 9cBpYLpCFmt

--HG--
extra : rebase_source : cf0899e8c5f5330d31c645cba27d1bd3fb19e814

python/mozbuild/mozbuild/frontend/emitter.py

@@ -1135,8 +1135,8 @@ class TreeMetadataEmitter(LoggingMixin):
             if (full_path == context.config.topsrcdir or
                     full_path == context.config.topobjdir):
                 raise SandboxValidationError('Path specified in LOCAL_INCLUDES '
-                    'is not allowed: %s (resolved to %s)' % (local_include,
-                    full_path), context)
+                    '(%s) resolves to the topsrcdir or topobjdir (%s), which is '
+                    'not allowed' % (local_include, full_path), context)
             include_obj = LocalInclude(context, local_include)
             local_includes.append(include_obj.path.full_path)
             yield include_obj

python/mozbuild/mozbuild/test/frontend/test_emitter.py

@@ -1041,14 +1041,16 @@ class TestEmitterBasic(unittest.TestCase):
 
         with self.assertRaisesRegexp(
                 SandboxValidationError,
-                'Path specified in LOCAL_INCLUDES is not allowed:'):
+                'Path specified in LOCAL_INCLUDES.*resolves to the '
+                'topsrcdir or topobjdir'):
             objs = self.read_topsrcdir(reader)
 
         reader = self.reader('local_includes-invalid/objdir')
 
         with self.assertRaisesRegexp(
                 SandboxValidationError,
-                'Path specified in LOCAL_INCLUDES is not allowed:'):
+                'Path specified in LOCAL_INCLUDES.*resolves to the '
+                'topsrcdir or topobjdir'):
             objs = self.read_topsrcdir(reader)
 
     def test_generated_includes(self):