[es6] implement default parameters via desugaring

src/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/bootstrapper.h"
 #include "src/messages.h"
 #include "src/parser.h"
@@ skipping 59 matching lines @@
 // ----------------------------------------------------------------------------
 // Implementation of Scope
 
 Scope::Scope(Zone* zone, Scope* outer_scope, ScopeType scope_type,
              AstValueFactory* ast_value_factory, FunctionKind function_kind)
     : inner_scopes_(4, zone),
       variables_(zone),
       internals_(4, zone),
       temps_(4, zone),
       params_(4, zone),
+      param_positions_(4, zone),
       unresolved_(16, zone),
       decls_(4, zone),
       module_descriptor_(
           scope_type == MODULE_SCOPE ? ModuleDescriptor::New(zone) : NULL),
       already_resolved_(false),
       ast_value_factory_(ast_value_factory),
       zone_(zone),
       class_declaration_group_start_(-1) {
   SetDefaults(scope_type, outer_scope, Handle<ScopeInfo>::null(),
               function_kind);
   // The outermost scope must be a script scope.
   DCHECK(scope_type == SCRIPT_SCOPE || outer_scope != NULL);
   DCHECK(!HasIllegalRedeclaration());
 }
 
 
 Scope::Scope(Zone* zone, Scope* inner_scope, ScopeType scope_type,
              Handle<ScopeInfo> scope_info, AstValueFactory* value_factory)
     : inner_scopes_(4, zone),
       variables_(zone),
       internals_(4, zone),
       temps_(4, zone),
       params_(4, zone),
+      param_positions_(4, zone),
       unresolved_(16, zone),
       decls_(4, zone),
       module_descriptor_(NULL),
       already_resolved_(true),
       ast_value_factory_(value_factory),
       zone_(zone),
       class_declaration_group_start_(-1) {
   SetDefaults(scope_type, NULL, scope_info);
   if (!scope_info.is_null()) {
     num_heap_slots_ = scope_info_->ContextLength();
   }
   // Ensure at least MIN_CONTEXT_SLOTS to indicate a materialized context.
   num_heap_slots_ = Max(num_heap_slots_,
                         static_cast<int>(Context::MIN_CONTEXT_SLOTS));
   AddInnerScope(inner_scope);
 }
 
 
 Scope::Scope(Zone* zone, Scope* inner_scope,
              const AstRawString* catch_variable_name,
              AstValueFactory* value_factory)
     : inner_scopes_(1, zone),
       variables_(zone),
       internals_(0, zone),
       temps_(0, zone),
       params_(0, zone),
+      param_positions_(0, zone),
       unresolved_(0, zone),
       decls_(0, zone),
       module_descriptor_(NULL),
       already_resolved_(true),
       ast_value_factory_(value_factory),
       zone_(zone),
       class_declaration_group_start_(-1) {
   SetDefaults(CATCH_SCOPE, NULL, Handle<ScopeInfo>::null());
   AddInnerScope(inner_scope);
   ++num_var_or_const_;
@@ skipping 37 matching lines @@
   force_eager_compilation_ = false;
   force_context_allocation_ = (outer_scope != NULL && !is_function_scope())
       ? outer_scope->has_forced_context_allocation() : false;
   num_var_or_const_ = 0;
   num_stack_slots_ = 0;
   num_heap_slots_ = 0;
   num_modules_ = 0;
   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;
   if (!scope_info.is_null()) {
     scope_calls_eval_ = scope_info->CallsEval();
     language_mode_ = scope_info->language_mode();
     block_scope_is_class_scope_ = scope_info->block_scope_is_class_scope();
     function_kind_ = scope_info->function_kind();
   }
 }
@@ skipping 256 matching lines @@
        scope != NULL;
        scope = scope->outer_scope()) {
     Variable* var = scope->LookupLocal(name);
     if (var != NULL) return var;
   }
   return NULL;
 }
 
 
 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,
                                      kCreatedInitialized);
   if (is_rest) {
     DCHECK_NULL(rest_parameter_);
     rest_parameter_ = var;
     rest_index_ = num_parameters();
   }
   // TODO(wingo): Avoid O(n^2) check.
   *is_duplicate = IsDeclaredParameter(name);
   params_.Add(var, zone());
+  param_positions_.Add(pos, zone());
   return var;
 }
 
 
 Variable* Scope::DeclareLocal(const AstRawString* name, VariableMode mode,
                               InitializationFlag init_flag, Variable::Kind kind,
                               MaybeAssignedFlag maybe_assigned_flag,
                               int declaration_group_start) {
   DCHECK(!already_resolved());
   // This function handles VAR, LET, and CONST modes.  DYNAMIC variables are
@@ skipping 50 matching lines @@
   temps_.Add(var, zone());
   return var;
 }
 
 
 void Scope::AddDeclaration(Declaration* declaration) {
   decls_.Add(declaration, zone());
 }
 
 
+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()) {
     illegal_redecl_ = expression;
   }
   DCHECK(HasIllegalRedeclaration());
 }
 
 
 void Scope::VisitIllegalRedeclaration(AstVisitor* visitor) {
@@ skipping 857 matching lines @@
       var->ForceContextAllocation();
     }
     AllocateParameter(var, i);
   }
 }
 
 
 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());

[caitp (gmail), 2015/05/26 17:14:07]

This is a hack to make sure the re-declared variables are properly context
allocated. It's finicky, and I don't think it's quite right, but I'm not 100%
sure how to verify it.

So this is really the area I'm most unsure about atm

[adamk, 2015/05/26 20:03:20]

Can we just skip the loop over params_ in AllocateParameterLocals() if
has_parameter_expressions_ is set? It seems like all the Variables in there are
bogus at this point if that bit is set (since they got "undeclared").

[caitp (gmail), 2015/05/26 20:24:44]

Maybe, but there are a few things that might go wrong

- The redeclared variable might need to be context allocated, which probably
won't happen without this check
- Stack and heap slot counts need to be what they're expected to be so that
scopeinfo ends up usable and sane

I'll try that after the next PS and see if it works reasonably well

[caitp (gmail), 2015/05/26 20:28:40]

Actually, it passes tests at the moment, so I guess this is fine

+      }
       DCHECK(var->IsUnallocated() || var->IsContextSlot());
       if (var->IsUnallocated()) {
         AllocateHeapSlot(var);
       }
     } else {
       DCHECK(var->IsUnallocated() || var->IsParameter());
       if (var->IsUnallocated()) {
         var->AllocateTo(Variable::PARAMETER, index);
       }
     }
@@ skipping 124 matching lines @@
       (function_ != NULL && function_->proxy()->var()->IsStackLocal() ? 1 : 0);
 }
 
 
 int Scope::ContextLocalCount() const {
   if (num_heap_slots() == 0) return 0;
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
       (function_ != NULL && function_->proxy()->var()->IsContextSlot() ? 1 : 0);
 }
 } }  // namespace v8::internal