Bindings generation emits (more) correct null checking

Source/bindings/dart/scripts/templates/interface_h.template

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // WARNING: Do not edit - generated code.
 
 #ifndef {{dart_class}}_h
 #define {{dart_class}}_h
 
 {% filter conditional(conditional_string) %}
@@ skipping 39 matching lines @@
         return toNative(value);
       {% else %}
         return 0;
       {% endif %}
     }
     static {{cpp_class}}* toNative(void* value)
     {
         return static_cast<{{cpp_class}}*>(value);
     }
 
+    // FIXME: This has redundant null checks, and much of this code should
+    // be moved to a common place to reduce code bloat.
+    // Convert to native, Dart_Null is an error
     static NativeType* toNative(Dart_Handle handle, Dart_Handle& exception)
     {
+        if (!Dart_IsNull(handle)) {
+            DartDOMData* domData = DartDOMData::current();
+            return DartDOMWrapper::unwrapDartWrapper<{{dart_class}}>(domData, handle, exception);
+        } else {
+            exception = Dart_NewStringFromCString("Null value is not a valid {{dart_class}}");
+            return 0;
+        }
+    }
+
+    // Convert nullable to native, Dart_Null maps to C++ null
+    static NativeType* toNativeWithNullCheck(Dart_Handle handle, Dart_Handle& exception)
+    {
         DartDOMData* domData = DartDOMData::current();
         return DartDOMWrapper::unwrapDartWrapper<{{dart_class}}>(domData, handle, exception);
     }
 
-    static NativeType* toNativeWithNullCheck(Dart_Handle handle, Dart_Handle& exception)
+    // Convert to native, Dart_Null is an error
+    static NativeType* toNative(Dart_NativeArguments args, int index, Dart_Handle& exception)
     {
-        return Dart_IsNull(handle) ? 0 : toNative(handle, exception);
+        NativeType* result = DartDOMWrapper::unwrapDartWrapper<{{dart_class}}>(args, index, exception);
+        if (result || exception) {
+            return result;
+        }
+        exception = Dart_NewStringFromCString("Null value is not a valid {{dart_class}}");
+        return 0;
     }
 
-    static NativeType* toNative(Dart_NativeArguments args, int index, Dart_Handle& exception)
+    // Convert nullable to native, Dart_Null maps to C++ null
+    static NativeType* toNativeWithNullCheck(Dart_NativeArguments args, int index, Dart_Handle& exception)
     {
         return DartDOMWrapper::unwrapDartWrapper<{{dart_class}}>(args, index, exception);
     }
 
-    static NativeType* toNativeWithNullCheck(Dart_NativeArguments args, int index, Dart_Handle& exception)
-    {
-        // toNative accounts for Null objects also.
-        return toNative(args, index, exception);
-    }
-
     static Dart_Handle toDart(NativeType* value)
     {
         if (!value)
             return Dart_Null();
         DartDOMData* domData = DartDOMData::current();
         Dart_WeakPersistentHandle result =
             DartDOMWrapper::lookupWrapper<{{dart_class}}>(domData, value);
         if (result)
             return Dart_HandleFromWeakPersistent(result);
         return createWrapper(domData, value);
@@ skipping 84 matching lines @@
   void propertyQuery(Dart_NativeArguments args);
   {% endif %}
 
 }
 
 }  // namespace WebCore
 
 {% endfilter %}
 
 #endif // {{dart_class}}_h