Mojom compiler: Improves error message by giving misspelled identifier.

mojo/public/tools/bindings/generators/mojom_cpp_generator.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Generates C++ source files from a mojom.Module."""
 
 import mojom.generate.generator as generator
 import mojom.generate.module as mojom
 import mojom.generate.pack as pack
 from mojom.generate.template_expander import UseJinja
@@ skipping 128 matching lines @@
   if mojom.IsGenericHandleKind(kind):
     return "mojo::ScopedHandle"
   if mojom.IsDataPipeConsumerKind(kind):
     return "mojo::ScopedDataPipeConsumerHandle"
   if mojom.IsDataPipeProducerKind(kind):
     return "mojo::ScopedDataPipeProducerHandle"
   if mojom.IsMessagePipeKind(kind):
     return "mojo::ScopedMessagePipeHandle"
   if mojom.IsSharedBufferKind(kind):
     return "mojo::ScopedSharedBufferHandle"
-  return _kind_to_cpp_type[kind]
+  # TODO(rudominer) After improvements to compiler front end have landed,
+  # revisit strategy used below for emitting a useful error message when an
+  # undefined identifier is referenced.
+  val =  _kind_to_cpp_type.get(kind)
+  if (val is not None):
+    return val
+  raise Exception("Unrecognized kind %s" % kind.spec)
 
 def GetCppWrapperType(kind):
   if mojom.IsEnumKind(kind):
     return GetNameForKind(kind)
   if mojom.IsStructKind(kind) or mojom.IsUnionKind(kind):
     return "%sPtr" % GetNameForKind(kind)
   if mojom.IsArrayKind(kind):
     return "mojo::Array<%s>" % GetCppArrayArgWrapperType(kind.kind)
   if mojom.IsMapKind(kind):
     return "mojo::Map<%s, %s>" % (GetCppArrayArgWrapperType(kind.key_kind),
@@ skipping 246 matching lines @@
   def GenerateModuleSource(self):
     return self.GetJinjaExports()
 
   def GenerateFiles(self, args):
     self.Write(self.GenerateModuleHeader(),
         self.MatchMojomFilePath("%s.h" % self.module.name))
     self.Write(self.GenerateModuleInternalHeader(),
         self.MatchMojomFilePath("%s-internal.h" % self.module.name))
     self.Write(self.GenerateModuleSource(),
         self.MatchMojomFilePath("%s.cc" % self.module.name))