dart2js cps: Ensure parameter default values are emitted.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, 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.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../closure.dart' show
     ClosureClassElement;
@@ skipping 54 matching lines @@
       new tree_ir.FallthroughStack();
 
   Set<tree_ir.Label> usedLabels = new Set<tree_ir.Label>();
 
   List<js.Statement> accumulator = new List<js.Statement>();
 
   CodeGenerator(this.glue, this.registry);
 
   /// Generates JavaScript code for the body of [function].
   js.Fun buildFunction(tree_ir.FunctionDefinition function) {
+    registerDefaultParameterValues(function.element);
     currentFunction = function.element;
     visitStatement(function.body);
 
     List<js.Parameter> parameters = new List<js.Parameter>();
     Set<tree_ir.Variable> parameterSet = new Set<tree_ir.Variable>();
     Set<String> declaredVariables = new Set<String>();
 
     for (tree_ir.Variable parameter in function.parameters) {
       String name = getVariableName(parameter);
       parameters.add(new js.Parameter(name));
@@ skipping 925 matching lines @@
   @override
   js.Expression visitAwait(tree_ir.Await node) {
     return new js.Await(visitExpression(node.input));
   }
 
   visitFunctionExpression(tree_ir.FunctionExpression node) {
     // FunctionExpressions are currently unused.
     // We might need them if we want to emit raw JS nested functions.
     throw 'FunctionExpressions should not be used';
   }
+
+  /// Ensures that parameter defaults will be emitted.
+  ///
+  /// Ideally, this should be done when generating the relevant stub methods,
+  /// since those are the ones that actually reference the constants, but those
+  /// are created by the emitter when it is too late to register new constants.
+  ///
+  /// For non-static methods, we have no way of knowing if the defaults are
+  /// actually used, so we conservatively register them all.
+  void registerDefaultParameterValues(ExecutableElement element) {
+    if (element is! FunctionElement) return;
+    FunctionElement function = element;
+    if (function.isStatic) return; // Defaults are inlined at call sites.
+    function.functionSignature.forEachOptionalParameter((param) {
+      ConstantValue constant = glue.getDefaultParameterValue(param);
+      registry.registerCompileTimeConstant(constant);
+    });
+  }
 }