[es6] implement optional parameters via desugaring (with scoping)

src/parser.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/api.h"
 #include "src/ast.h"
 #include "src/bailout-reason.h"
 #include "src/base/platform/platform.h"
@@ skipping 1115 matching lines @@
               ? FunctionLiteral::ANONYMOUS_EXPRESSION
               : FunctionLiteral::NAMED_EXPRESSION)
         : FunctionLiteral::DECLARATION;
     bool ok = true;
 
     if (shared_info->is_arrow()) {
       Scope* scope = NewScope(scope_, ARROW_SCOPE);
       scope->set_start_position(shared_info->start_position());
       FormalParameterErrorLocations error_locs;
       bool has_rest = false;
+      bool has_initializers = false;
+      ZoneList<Expression*>* initializers =
+          new (zone()) ZoneList<Expression*>(0, zone());
       if (Check(Token::LPAREN)) {
         // '(' StrictFormalParameters ')'
-        ParseFormalParameterList(scope, &error_locs, &has_rest, &ok);
+        Scope* parameter_scope = NewScope(scope, PARAMETER_SCOPE);
+        ParseFormalParameterList(scope, parameter_scope, &error_locs,
+                                 initializers, &has_initializers,
+                                 &has_rest, &ok);
         if (ok) ok = Check(Token::RPAREN);
       } else {
         // BindingIdentifier
-        ParseFormalParameter(scope, &error_locs, has_rest, &ok);
+        ParseFormalParameter(scope, nullptr, &error_locs,
+                             nullptr, nullptr, has_rest, &ok);
       }
 
       if (ok) {
         ExpressionClassifier classifier;
         Expression* expression = ParseArrowFunctionLiteral(
             scope, error_locs, has_rest, &classifier, &ok);
         // TODO(dslomov): report error if not a valid expression.
         if (ok) {
           // Scanning must end at the same position that was recorded
           // previously. If not, parsing has been interrupted due to a stack
@@ skipping 2736 matching lines @@
     // TODO(wingo): Make a better message.
     ReportMessageAt(params_loc, "malformed_arrow_function_parameter_list");
     *ok = false;
     return;
   }
 
   DeclareArrowFunctionParameters(scope, params, params_loc, error_locs, ok);
 }
 
 
+ZoneList<Statement*>* Parser::DesugarInitializeParameters(
+    bool has_initializers, ZoneList<Expression*>* initializers) {
+  ZoneList<Statement*>* body = new (zone()) ZoneList<Statement*>(0, zone());
+  if (has_initializers) {
+    for (int i = 0; i < initializers->length(); ++i) {
+      Expression* initializer = initializers->at(i);
+      // TODO(caitp): ensure proper TDZ behaviour --- need hole-check for
+      // all parameter bindings, including ones without initializers
+      if (initializer) {
+        // IS_UNDEFINED(%_Arguments(i)) ? <initializer> : %_Arguments(i);
+        const AstRawString* fn_name = ast_value_factory()->empty_string();
+        const Runtime::Function* arguments =
+            Runtime::FunctionForId(Runtime::kInlineArguments);
+        ZoneList<Expression*>* arguments_i0 =
+            new (zone()) ZoneList<Expression*>(0, zone());
+        arguments_i0->Add(
+            factory()->NewSmiLiteral(i, RelocInfo::kNoPosition), zone());
+
+        ZoneList<Expression*>* arguments_i1 =
+            new (zone()) ZoneList<Expression*>(0, zone());
+        arguments_i1->Add(
+            factory()->NewSmiLiteral(i, RelocInfo::kNoPosition), zone());
+
+        Expression* arg_or_default = factory()->NewConditional(
+            // condition:
+            factory()->NewCompareOperation(
+                Token::EQ_STRICT,
+                factory()->NewCallRuntime(fn_name, arguments, arguments_i0,
+                                          RelocInfo::kNoPosition),
+                factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
+                RelocInfo::kNoPosition),
+            // if true:
+            initializer,
+            // if false:
+            factory()->NewCallRuntime(fn_name, arguments, arguments_i1,
+                                      RelocInfo::kNoPosition),
+            RelocInfo::kNoPosition);
+
+        Expression* assign = factory()->NewAssignment(
+            Token::ASSIGN,
+            factory()->NewVariableProxy(
+                scope_->parameter(i), RelocInfo::kNoPosition),
+            arg_or_default,
+            RelocInfo::kNoPosition);
+
+        body->Add(
+            factory()->NewExpressionStatement(
+                assign, RelocInfo::kNoPosition),
+            zone());
+      }
+    }
+  }
+  return body;
+}
+
+
 FunctionLiteral* Parser::ParseFunctionLiteral(
     const AstRawString* function_name, Scanner::Location function_name_location,
     bool name_is_strict_reserved, FunctionKind kind, int function_token_pos,
     FunctionLiteral::FunctionType function_type,
     FunctionLiteral::ArityRestriction arity_restriction, bool* ok) {
   // Function ::
   //   '(' FormalParameterList? ')' '{' FunctionBody '}'
   //
   // Getter ::
   //   '(' ')' '{' FunctionBody '}'
@@ skipping 45 matching lines @@
   //   compiling a function in an inner declaration scope in the eval, e.g. a
   //   nested function, and hoisting works normally relative to that.
   Scope* declaration_scope = scope_->DeclarationScope();
   Scope* original_declaration_scope = original_scope_->DeclarationScope();
   Scope* scope = function_type == FunctionLiteral::DECLARATION &&
                          is_sloppy(language_mode()) &&
                          (original_scope_ == original_declaration_scope ||
                           declaration_scope != original_declaration_scope)
                      ? NewScope(declaration_scope, FUNCTION_SCOPE, kind)
                      : NewScope(scope_, FUNCTION_SCOPE, kind);
+  Scope* parameter_scope = NewScope(scope, PARAMETER_SCOPE);
   ZoneList<Statement*>* body = NULL;
   int materialized_literal_count = -1;
   int expected_property_count = -1;
   int handler_count = 0;
   FormalParameterErrorLocations error_locs;
   FunctionLiteral::EagerCompileHint eager_compile_hint =
       parenthesized_function_ ? FunctionLiteral::kShouldEagerCompile
                               : FunctionLiteral::kShouldLazyCompile;
   // Parse function body.
   {
@@ skipping 13 matching lines @@
       // expressions. This also marks the FunctionState as a generator.
       Variable* temp = scope_->DeclarationScope()->NewTemporary(
           ast_value_factory()->dot_generator_object_string());
       function_state.set_generator_object_variable(temp);
     }
 
     bool has_rest = false;
     Expect(Token::LPAREN, CHECK_OK);
     int start_position = scanner()->location().beg_pos;
     scope_->set_start_position(start_position);
-    num_parameters =
-        ParseFormalParameterList(scope, &error_locs, &has_rest, CHECK_OK);
+    ZoneList<Expression*>* initializers =
+        new (zone()) ZoneList<Expression*>(0, zone());
+    bool has_initializers = false;
+    num_parameters = ParseFormalParameterList(scope, parameter_scope,
+                                              &error_locs, initializers,
+                                              &has_initializers, &has_rest,
+                                              CHECK_OK);
     Expect(Token::RPAREN, CHECK_OK);
     int formals_end_position = scanner()->location().end_pos;
 
     CheckArityRestrictions(num_parameters, arity_restriction, start_position,
                            formals_end_position, CHECK_OK);
 
     Expect(Token::LBRACE, CHECK_OK);
 
     // If we have a named function expression, we add a local variable
     // declaration to the body of the function with the name of the
@@ skipping 58 matching lines @@
     parenthesized_function_ = false;  // The bit was set for this function only.
 
     if (is_lazily_parsed) {
       for (Scope* s = scope_->outer_scope();
            s != nullptr && (s != s->DeclarationScope()); s = s->outer_scope()) {
         s->ForceContextAllocation();
       }
       SkipLazyFunctionBody(&materialized_literal_count,
                            &expected_property_count, CHECK_OK);
     } else {
-      body = ParseEagerFunctionBody(function_name, pos, fvar, fvar_init_op,
-                                    kind, CHECK_OK);
+      body = DesugarInitializeParameters(has_initializers, initializers);
+      ZoneList<Statement*>* inner_body =
+          ParseEagerFunctionBody(function_name, pos, fvar, fvar_init_op,
+                                 kind, CHECK_OK);
+      body->AddAll(*inner_body, zone());
       materialized_literal_count = function_state.materialized_literal_count();
       expected_property_count = function_state.expected_property_count();
       handler_count = function_state.handler_count();
 
       if (is_strong(language_mode()) && IsSubclassConstructor(kind)) {
         if (!function_state.super_location().IsValid()) {
           ReportMessageAt(function_name_location,
                           "strong_super_call_missing", kReferenceError);
           *ok = false;
           return nullptr;
@@ skipping 1733 matching lines @@
 
 Expression* Parser::SpreadCallNew(Expression* function,
                                   ZoneList<v8::internal::Expression*>* args,
                                   int pos) {
   args->InsertAt(0, function, zone());
 
   return factory()->NewCallRuntime(
       ast_value_factory()->reflect_construct_string(), NULL, args, pos);
 }
 } }  // namespace v8::internal