Force named arguments in constructors.

lib/html/scripts/generator.py

Index: lib/html/scripts/generator.py
diff --git a/lib/html/scripts/generator.py b/lib/html/scripts/generator.py
index 8fabd064fc4d2aa8ccf426c22556c551affd2434..8b9712e467b56593792ce8d5c9bbb27beba5a5b8 100644
--- a/lib/html/scripts/generator.py
+++ b/lib/html/scripts/generator.py
@@ -237,6 +237,7 @@ def AnalyzeOperation(interface, operations):
   info.js_name = info.declared_name
   info.type_name = operations[0].type.id   # TODO: widen.
   info.param_infos = _BuildArguments([op.arguments for op in split_operations], interface)
+  info.requires_named_arguments = False
   return info
 
 
@@ -270,6 +271,7 @@ def AnalyzeConstructor(interface):
   info.js_name = name
   info.type_name = interface.id
   info.param_infos = args
+  info.requires_named_arguments = False
   return info
 
 def IsDartListType(type):
@@ -339,9 +341,10 @@ class OperationInfo(object):
     param_infos: A list of ParamInfo.
   """
 
-  def ParametersInterfaceDeclaration(self, rename_type):
+  def ParametersInterfaceDeclaration(self, rename_type, force_optional=False):
     """Returns a formatted string declaring the parameters for the interface."""
-    return self._FormatParams(self.param_infos, rename_type, True)
+    return self._FormatParams(self.param_infos, rename_type, True,
+                              force_optional=force_optional)
 
   def ParametersImplementationDeclaration(self, rename_type):
     """Returns a formatted string declaring the parameters for the
@@ -363,7 +366,8 @@ class OperationInfo(object):
         lambda param_info: param_info.name,
         self.param_infos[:parameter_count]))
 
-  def _FormatParams(self, params, rename_type, provide_comments):
+  def _FormatParams(self, params, rename_type, provide_comments,
+                    force_optional=False):
     def FormatParam(param):
       dart_type = rename_type(param.type_id) if param.type_id else 'Dynamic'
       type = TypeOrNothing(dart_type, param.type_id if provide_comments else None)
@@ -381,7 +385,12 @@ class OperationInfo(object):
         required.append(param_info)
     argtexts = map(FormatParam, required)
     if optional:
-      argtexts.append('[' + ', '.join(map(FormatParam, optional)) + ']')
+      needs_named = self.requires_named_arguments and not force_optional
+      left_bracket, right_bracket = '{}' if needs_named else '[]'
+      argtexts.append(
+          left_bracket +
+          ', '.join(map(FormatParam, optional)) +
+          right_bracket)
     return ', '.join(argtexts)
 
   def IsStatic(self):