Bug 1476973 - part 2 - assert that XPIDL_SOURCES files all exist; r=gps

We should have been checking for this from the beginning.

python/mozbuild/mozbuild/frontend/emitter.py

@@ -1385,6 +1385,10 @@ class TreeMetadataEmitter(LoggingMixin):
                 '{path}: DIST_INSTALL = False has no effect on XPIDL_SOURCES.')
 
         for idl in context['XPIDL_SOURCES']:
+            if not os.path.exists(idl.full_path):
+                raise SandboxValidationError('File %s from XPIDL_SOURCES '
+                    'does not exist' % idl.full_path, context)
+
             yield XPIDLFile(context, idl, xpidl_module)
 
     def _process_generated_files(self, context):

python/mozbuild/mozbuild/test/frontend/data/missing-xpidl/moz.build

@@ -0,0 +1,6 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# Any copyright is dedicated to the Public Domain.
+# http://creativecommons.org/publicdomain/zero/1.0/
+
+XPIDL_MODULE = 'my_module'
+XPIDL_SOURCES = ['nonexistant.idl']

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

@@ -1127,6 +1127,13 @@ class TestEmitterBasic(unittest.TestCase):
             reader = self.reader('xpidl-module-no-sources')
             self.read_topsrcdir(reader)
 
+    def test_xpidl_module_no_sources(self):
+        """Missing XPIDL_SOURCES should be rejected."""
+        with self.assertRaisesRegexp(SandboxValidationError, 'File .* '
+            'from XPIDL_SOURCES does not exist'):
+            reader = self.reader('missing-xpidl')
+            self.read_topsrcdir(reader)
+
     def test_missing_local_includes(self):
         """LOCAL_INCLUDES containing non-existent directories should be rejected."""
         with self.assertRaisesRegexp(SandboxValidationError, 'Path specified in '