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

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index feed1e4b12fcef812309dfe4c4a7870fbcd41a13..f0641d4e84b40a06582c75d264df16b8944277f8 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -1134,13 +1134,18 @@ FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
       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);
+        ParseFormalParameterList(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, &error_locs, nullptr, nullptr, has_rest,
+                             &ok);
       }
 
       if (ok) {
@@ -1925,7 +1930,8 @@ VariableProxy* Parser::NewUnresolved(const AstRawString* name,
 }
 
 
-Variable* Parser::Declare(Declaration* declaration, bool resolve, bool* ok) {
+Variable* Parser::Declare(Declaration* declaration, bool resolve,
+                          bool allow_redeclaration, bool* ok) {
   VariableProxy* proxy = declaration->proxy();
   DCHECK(proxy->raw_name() != NULL);
   const AstRawString* name = proxy->raw_name();
@@ -1948,7 +1954,7 @@ Variable* Parser::Declare(Declaration* declaration, bool resolve, bool* ok) {
       declaration_scope->is_script_scope()) {
     // Declare the variable in the declaration scope.
     var = declaration_scope->LookupLocal(name);
-    if (var == NULL) {
+    if (var == NULL || allow_redeclaration) {
       // Declare the name.
       Variable::Kind kind = Variable::NORMAL;
       int declaration_group_start = -1;
@@ -1960,9 +1966,16 @@ Variable* Parser::Declare(Declaration* declaration, bool resolve, bool* ok) {
         declaration_group_start =
             declaration->AsVariableDeclaration()->declaration_group_start();
       }
-      var = declaration_scope->DeclareLocal(
-          name, mode, declaration->initialization(), kind, kNotAssigned,
-          declaration_group_start);
+      if (var) {
+        DCHECK(declaration_scope->IsDeclaredParameter(name));
+        var = declaration_scope->RedeclareLocal(
+            name, mode, declaration->initialization(), kind, kNotAssigned,
+            declaration_group_start);
+      } else {
+        var = declaration_scope->DeclareLocal(
+            name, mode, declaration->initialization(), kind, kNotAssigned,
+            declaration_group_start);
+      }
     } else if (IsLexicalVariableMode(mode) ||
                IsLexicalVariableMode(var->mode()) ||
                ((mode == CONST_LEGACY || var->mode() == CONST_LEGACY) &&
@@ -3930,9 +3943,9 @@ void ParserTraits::DeclareArrowFunctionParameters(
   // VariableProxy and recorded as unresolved in the scope.  Here we undo that
   // parse-time side-effect.
   parser_->scope_->RemoveUnresolved(expr->AsVariableProxy());
-
+  int pos = expr->AsVariableProxy()->position();
   bool is_rest = false;
-  bool is_duplicate = DeclareFormalParameter(scope, raw_name, is_rest);
+  bool is_duplicate = DeclareFormalParameter(scope, raw_name, is_rest, pos);
 
   if (is_duplicate) {
     // Arrow function parameter lists are parsed as StrictFormalParameters,
@@ -3963,6 +3976,98 @@ void ParserTraits::ParseArrowFunctionFormalParameters(
 }
 
 
+ZoneList<Statement*>* Parser::DesugarInitializeParameters(
+    Scope* scope, bool has_initializers, ZoneList<Expression*>* initializers) {
+  DCHECK(scope->is_function_scope());
+
+  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);
+
+      // Position of parameter VariableProxy, for hole-checking
+      int pos = scope->parameter_position(i);
+
+      // Lexically declare the initialized variable
+      static const VariableMode mode = LET;
+      VariableProxy* proxy =
+          NewUnresolved(scope->parameter(i)->raw_name(), mode);
+      VariableDeclaration* declaration = factory()->NewVariableDeclaration(
+          proxy, mode, scope, RelocInfo::kNoPosition);
+      // BRITTLE: this illegally redeclares the variable, be careful about this
+      proxy =
+          factory()->NewVariableProxy(Declare(declaration, true, true), pos);
+      proxy->var()->set_maybe_assigned();
+
+      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());
+
+      // 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);
+        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::INIT_LET, proxy, arg_or_default, RelocInfo::kNoPosition);
+
+        body->Add(
+            factory()->NewExpressionStatement(assign, RelocInfo::kNoPosition),
+            zone());
+        proxy->var()->set_initializer_position(initializer->position());
+      } else {
+        // let <name> = %_Arguments(i)
+        Expression* assign = factory()->NewAssignment(
+            Token::INIT_LET, proxy,
+            factory()->NewCallRuntime(fn_name, arguments, arguments_i0,
+                                      RelocInfo::kNoPosition),
+            RelocInfo::kNoPosition);
+        body->Add(
+            factory()->NewExpressionStatement(assign, RelocInfo::kNoPosition),
+            zone());
+        proxy->var()->set_initializer_position(pos);
+      }
+    }
+  } else {
+    // If hasParameterExpressions is false, remove the unnecessary parameter
+    // block scopes. The function body scope can't be safely removed at this
+    // point.
+    ZoneList<Scope*>* scopes = scope->inner_scopes();
+    for (int i = 0; i < scopes->length(); ++i) {
+      Scope* scope = scopes->at(i);
+      if (!scope->is_function_body_scope()) {
+        DCHECK(scope->is_block_scope());
+        scope->FinalizeBlockScope();
+      }
+    }
+  }
+  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,
@@ -4028,6 +4133,8 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
                           declaration_scope != original_declaration_scope)
                      ? NewScope(declaration_scope, FUNCTION_SCOPE, kind)
                      : NewScope(scope_, FUNCTION_SCOPE, kind);
+  Scope* function_body = NewScope(scope, FUNCTION_BODY_SCOPE);
+  DCHECK_EQ(scope->function_body(), function_body);
   ZoneList<Statement*>* body = NULL;
   int materialized_literal_count = -1;
   int expected_property_count = -1;
@@ -4042,6 +4149,7 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
     FunctionState function_state(&function_state_, &scope_, scope, kind,
                                  &function_factory);
     scope_->SetScopeName(function_name);
+    function_body->SetScopeName(function_name);
 
     if (is_generator) {
       // For generators, allocating variables in contexts is currently a win
@@ -4061,8 +4169,13 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
     Expect(Token::LPAREN, CHECK_OK);
     int start_position = scanner()->location().beg_pos;
     scope_->set_start_position(start_position);
+    function_body->set_start_position(start_position);
+    ZoneList<Expression*>* initializers =
+        new (zone()) ZoneList<Expression*>(0, zone());
+    bool has_initializers = false;
     num_parameters =
-        ParseFormalParameterList(scope, &error_locs, &has_rest, CHECK_OK);
+        ParseFormalParameterList(scope, &error_locs, initializers,
+                                 &has_initializers, &has_rest, CHECK_OK);
     Expect(Token::RPAREN, CHECK_OK);
     int formals_end_position = scanner()->location().end_pos;
 
@@ -4092,6 +4205,7 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
       VariableProxy* proxy = factory()->NewVariableProxy(fvar);
       VariableDeclaration* fvar_declaration = factory()->NewVariableDeclaration(
           proxy, fvar_mode, scope_, RelocInfo::kNoPosition);
+      DCHECK(scope_->is_function_scope());
       scope_->DeclareFunctionVar(fvar_declaration);
     }
 
@@ -4133,26 +4247,47 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
                              !parenthesized_function_);
     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();
+    {
+      // Use the FUNCTION_BODY scope only if it's needed
+      // TODO(caitp): This is needed when ObjectBindingPatterns with
+      // computed property keys are used as well.
+      Scope* func_scope = has_initializers ? function_body : scope_;
+      if (func_scope != function_body) {
+        function_body->FinalizeBlockScope();
       }
-      SkipLazyFunctionBody(&materialized_literal_count,
-                           &expected_property_count, CHECK_OK);
-    } else {
-      body = ParseEagerFunctionBody(function_name, pos, fvar, fvar_init_op,
-                                    kind, CHECK_OK);
-      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;
+
+      if (is_lazily_parsed) {
+        for (Scope* s = scope_->outer_scope();
+             s != nullptr && (s != s->DeclarationScope());
+             s = s->outer_scope()) {
+          s->ForceContextAllocation();
+        }
+        {
+          BlockState function_body_state(&scope_, func_scope);
+          SkipLazyFunctionBody(&materialized_literal_count,
+                               &expected_property_count, CHECK_OK);
+        }
+      } else {
+        body =
+            DesugarInitializeParameters(scope, has_initializers, initializers);
+        {
+          BlockState function_body_state(&scope_, func_scope);
+          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;
+          }
         }
       }
     }
@@ -4244,6 +4379,10 @@ void Parser::SkipLazyFunctionBody(int* materialized_literal_count,
     return;
   }
   scope_->set_end_position(logger.end());
+  if (scope_->is_function_body_scope()) {
+    DCHECK(scope_->outer_scope()->is_function_scope());
+    scope_->outer_scope()->set_end_position(scanner()->location().end_pos);
+  }
   Expect(Token::RBRACE, ok);
   if (!*ok) {
     return;
@@ -4352,6 +4491,10 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
 
   Expect(Token::RBRACE, CHECK_OK);
   scope_->set_end_position(scanner()->location().end_pos);
+  if (scope_->is_function_body_scope()) {
+    DCHECK(scope_->outer_scope()->is_function_scope());
+    scope_->outer_scope()->set_end_position(scanner()->location().end_pos);
+  }
 
   return body;
 }