Bindings generation emits (more) correct null checking

Source/bindings/dart/scripts/dart_types.py

Index: Source/bindings/dart/scripts/dart_types.py
diff --git a/Source/bindings/dart/scripts/dart_types.py b/Source/bindings/dart/scripts/dart_types.py
index d7d94bceca3946677d8abca6b567f69d77fc6ab0..1ca39fb5ae9a44b5e34c20896ebf70bda7c50533 100644
--- a/Source/bindings/dart/scripts/dart_types.py
+++ b/Source/bindings/dart/scripts/dart_types.py
@@ -399,7 +399,7 @@ DART_TO_CPP_VALUE = {
 }
 
 
-def dart_value_to_cpp_value(idl_type, extended_attributes, variable_name,
+def dart_value_to_cpp_value(idl_type, interface_extended_attributes, extended_attributes, variable_name,
                             null_check, index, auto_scope=True):
     # Composite types
     array_or_sequence_type = idl_type.array_or_sequence_type
@@ -425,7 +425,8 @@ def dart_value_to_cpp_value(idl_type, extended_attributes, variable_name,
         # FIXME(vsm): When do we call the externalized version? E.g., see
         # bindings/dart/custom/DartWaveShaperNodeCustom.cpp - it calls
         # DartUtilities::dartToExternalizedArrayBufferView instead.
-        cpp_expression_format = ('DartUtilities::dartTo{idl_type}{null_check}(args, {index}, exception)')
+        # V8 always converts null here
+        cpp_expression_format = ('DartUtilities::dartTo{idl_type}WithNullCheck(args, {index}, exception)')
     elif idl_type.is_callback_interface:
         cpp_expression_format = ('Dart{idl_type}::create{null_check}(args, {index}, exception)')
     else:
@@ -435,8 +436,7 @@ def dart_value_to_cpp_value(idl_type, extended_attributes, variable_name,
     # some cases that require calling context info.  V8 handles all
     # of this differently, and we may wish to reconsider this approach
     null_check = 'WithNullCheck' \
-        if null_check or allow_null(idl_type, extended_attributes) else ''
-
+        if null_check or allow_null(idl_type, interface_extended_attributes, extended_attributes) else ''
     return cpp_expression_format.format(null_check=null_check,
                                         arguments=arguments,
                                         index=index,
@@ -469,14 +469,14 @@ def dart_value_to_cpp_value_array_or_sequence(array_or_sequence_type, variable_n
     return expression
 
 
-def dart_value_to_local_cpp_value(idl_type, extended_attributes, variable_name,
-                                  null_check, index=None, auto_scope=True):
+def dart_value_to_local_cpp_value(idl_type, interface_extended_attributes, extended_attributes,
+                                  variable_name, null_check, index=None, auto_scope=True):
     """Returns an expression that converts a Dart value to a C++ value as a local value."""
     idl_type = idl_type.preprocessed_type
 
     cpp_value = dart_value_to_cpp_value(
-        idl_type, extended_attributes, variable_name, null_check, index,
-        auto_scope)
+        idl_type, interface_extended_attributes, extended_attributes,
+        variable_name, null_check, index, auto_scope)
 
     return cpp_value
 
@@ -753,22 +753,43 @@ IdlType.name = property(dart_name)
 IdlUnionType.name = property(dart_name)
 
 
+def typechecked_interface(extended_attributes):
+    return ('TypeChecking' in extended_attributes and\
+            DartUtilities.extended_attribute_value_contains(extended_attributes['TypeChecking'], 'Interface'))
+
+
+def typechecked_argument(idl_type, interface_extended_attributes, extended_attributes):
+    return (idl_type.is_wrapper_type and
+            (typechecked_interface(interface_extended_attributes) or
+            (typechecked_interface(extended_attributes))))
+
+
 # If True use the WithNullCheck version when converting.
-def allow_null(idl_type, extended_attributes):
+def allow_null(idl_type, interface_extended_attributes, extended_attributes):
+    if idl_type.base_type in ('DOMString', 'ByteString', 'ScalarValueString'):
+        # This logic is in cpp_types in v8_types.py, since they handle
+        # this using the V8StringResource type.  We handle it here
+        if (extended_attributes.get('TreatNullAs') == 'NullString' or
+            extended_attributes.get('TreatUndefinedAs') == 'NullString'):
+            return True
+
+        if extended_attributes.get('Default') == 'NullString':
+            return True
 
-    # This logic is implemented in the methods.cpp template in V8
-    if idl_type.is_nullable:
-        return True
+        if extended_attributes.get('Default') == 'Undefined':
+            return True
 
-    if extended_attributes.get('Default') == 'NullString':
-        return True
+        if idl_type.is_nullable:
+            return True
+
+        return False
+    else:
+        # This logic is implemented in the methods.cpp template in V8
+        if (idl_type.is_nullable or
+           (not typechecked_argument(idl_type, interface_extended_attributes, extended_attributes))):
+            return True
 
-    if extended_attributes.get('Default') == 'Undefined':
-        return True
+        if extended_attributes.get('Default') == 'Undefined':
+            return True
 
-    # This logic is in cpp_types in v8_types.py, since they handle
-    # this using the V8StringResource type.  We handle it here
-    if (extended_attributes.get('TreatNullAs') == 'NullString' or
-        extended_attributes.get('TreatUndefinedAs') == 'NullString'):
-        return True
-    return False
+        return False