[es6] implement default parameters via desugaring

src/scopes.cc

Index: src/scopes.cc
diff --git a/src/scopes.cc b/src/scopes.cc
index 60c14dbdc8d752af1cb209897c97eb7d944f553e..9f682381432cb70a11c6c57182bb79b72daa2f23 100644
--- a/src/scopes.cc
+++ b/src/scopes.cc
@@ -77,6 +77,7 @@ Scope::Scope(Zone* zone, Scope* outer_scope, ScopeType scope_type,
       internals_(4, zone),
       temps_(4, zone),
       params_(4, zone),
+      param_positions_(4, zone),
       unresolved_(16, zone),
       decls_(4, zone),
       module_descriptor_(
@@ -100,6 +101,7 @@ Scope::Scope(Zone* zone, Scope* inner_scope, ScopeType scope_type,
       internals_(4, zone),
       temps_(4, zone),
       params_(4, zone),
+      param_positions_(4, zone),
       unresolved_(16, zone),
       decls_(4, zone),
       module_descriptor_(NULL),
@@ -126,6 +128,7 @@ Scope::Scope(Zone* zone, Scope* inner_scope,
       internals_(0, zone),
       temps_(0, zone),
       params_(0, zone),
+      param_positions_(0, zone),
       unresolved_(0, zone),
       decls_(0, zone),
       module_descriptor_(NULL),
@@ -183,6 +186,7 @@ void Scope::SetDefaults(ScopeType scope_type, Scope* outer_scope,
   module_var_ = NULL,
   rest_parameter_ = NULL;
   rest_index_ = -1;
+  has_parameter_expressions_ = false;
   scope_info_ = scope_info;
   start_position_ = RelocInfo::kNoPosition;
   end_position_ = RelocInfo::kNoPosition;
@@ -459,7 +463,7 @@ Variable* Scope::Lookup(const AstRawString* name) {
 
 
 Variable* Scope::DeclareParameter(const AstRawString* name, VariableMode mode,
-                                  bool is_rest, bool* is_duplicate) {
+                                  bool is_rest, bool* is_duplicate, int pos) {
   DCHECK(!already_resolved());
   DCHECK(is_function_scope());
   Variable* var = variables_.Declare(this, name, mode, Variable::NORMAL,
@@ -472,6 +476,7 @@ Variable* Scope::DeclareParameter(const AstRawString* name, VariableMode mode,
   // TODO(wingo): Avoid O(n^2) check.
   *is_duplicate = IsDeclaredParameter(name);
   params_.Add(var, zone());
+  param_positions_.Add(pos, zone());
   return var;
 }
 
@@ -542,6 +547,18 @@ void Scope::AddDeclaration(Declaration* declaration) {
 }
 
 
+void Scope::UndeclareParametersForExpressions() {
+  DCHECK(is_function_scope());
+  DCHECK(!has_parameter_expressions_);
+  has_parameter_expressions_ = true;
+  for (int i = 0; i < num_parameters(); ++i) {
+    Variable* p = parameter(i);
+    const AstRawString* name = p->raw_name();
+    variables_.Remove(const_cast<AstRawString*>(name), name->hash());
+  }
+}
+
+
 void Scope::SetIllegalRedeclaration(Expression* expression) {
   // Record only the first illegal redeclaration.
   if (!HasIllegalRedeclaration()) {
@@ -1419,6 +1436,11 @@ void Scope::AllocateParameterLocals(Isolate* isolate) {
 void Scope::AllocateParameter(Variable* var, int index) {
   if (MustAllocate(var)) {
     if (MustAllocateInContext(var)) {
+      if (has_parameter_expressions_) {
+        // If hasParameterExpressions is true, context-allocate the redeclared
+        // lexical variable, not the function parameter.
+        var = variables_.Lookup(var->raw_name());
+      }
       DCHECK(var->IsUnallocated() || var->IsContextSlot());
       if (var->IsUnallocated()) {
         AllocateHeapSlot(var);