[es6] Re-implement rest parameters via desugaring.

src/preparser.h

 // 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.
 
 #ifndef V8_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/bailout-reason.h"
 #include "src/expression-classifier.h"
 #include "src/func-name-inferrer.h"
@@ skipping 13 matching lines @@
   kFunctionNameValidityUnknown
 };
 
 
 struct FormalParametersBase {
   explicit FormalParametersBase(Scope* scope) : scope(scope) {}
   Scope* scope;
   bool has_rest = false;
   bool is_simple = true;
   int materialized_literals_count = 0;
+  mutable int rest_array_literal_index = -1;
 };
 
 
 // Common base class shared between parser and pre-parser. Traits encapsulate
 // the differences between Parser and PreParser:
 
 // - Return types: For example, Parser functions return Expression* and
 // PreParser functions return PreParserExpression.
 
 // - Creating parse tree nodes: Parser generates an AST during the recursive
@@ skipping 866 matching lines @@
   }
 
   static PreParserExpression FromIdentifier(PreParserIdentifier id) {
     return PreParserExpression(TypeField::encode(kIdentifierExpression) |
                                IdentifierTypeField::encode(id.type_));
   }
 
   static PreParserExpression BinaryOperation(PreParserExpression left,
                                              Token::Value op,
                                              PreParserExpression right) {
-    return PreParserExpression(TypeField::encode(kBinaryOperationExpression));
+    return PreParserExpression(
+        TypeField::encode(kBinaryOperationExpression) |
+        HasRestField::encode(op == Token::COMMA &&
+                             right->IsSpreadExpression()));
   }
 
   static PreParserExpression StringLiteral() {
     return PreParserExpression(TypeField::encode(kStringLiteralExpression));
   }
 
   static PreParserExpression UseStrictStringLiteral() {
     return PreParserExpression(TypeField::encode(kStringLiteralExpression) |
                                IsUseStrictField::encode(true));
   }
@@ skipping 96 matching lines @@
 
   bool IsNoTemplateTag() const {
     return TypeField::decode(code_) == kExpression &&
            ExpressionTypeField::decode(code_) == kNoTemplateTagExpression;
   }
 
   bool IsSpreadExpression() const {
     return TypeField::decode(code_) == kSpreadExpression;
   }
 
+  bool HasRestParameter() const {
+    // Preparser's way of determining if an arrow function has a rest parameter.
+    return IsSpreadExpression() ||
+           (IsBinaryOperation() && HasRestField::decode(code_));

[wingo, 2015/08/31 13:07:31]

Need more comments about the preconditions, i.e. the result is only valid on the
result of ParseConditionalExpression when the conditional expression stared with
an LPAREN and the classifier returns true for
is_valid_arrow_formal_parameters().  Actually I think this would be better
inlined into the trait-specific ParseArrowFunctionFormalParameters.

[caitp (gmail), 2015/08/31 13:23:40]

I'll inline it

[caitp (gmail), 2015/08/31 13:28:17]

Actually, it can't really be inlined since there's no way to get at the
bitfield, and it's really more code to change that and inline it.

How would you feel about the name just indicating it's specific to arrow
function parameters?

+  }
+
   PreParserExpression AsFunctionLiteral() { return *this; }
 
   bool IsBinaryOperation() const {
     return TypeField::decode(code_) == kBinaryOperationExpression;
   }
 
   // Dummy implementation for making expression->somefunc() work in both Parser
   // and PreParser.
   PreParserExpression* operator->() { return this; }
 
@@ skipping 28 matching lines @@
   // The first three bits are for the Type.
   typedef BitField<Type, 0, 3> TypeField;
 
   // The rest of the bits are interpreted depending on the value
   // of the Type field, so they can share the storage.
   typedef BitField<ExpressionType, TypeField::kNext, 3> ExpressionTypeField;
   typedef BitField<bool, TypeField::kNext, 1> IsUseStrictField;
   typedef BitField<bool, IsUseStrictField::kNext, 1> IsUseStrongField;
   typedef BitField<PreParserIdentifier::Type, TypeField::kNext, 10>
       IdentifierTypeField;
+  typedef BitField<bool, TypeField::kNext, 1> HasRestField;
 
   uint32_t code_;
 };
 
 
 // The pre-parser doesn't need to build lists of expressions, identifiers, or
 // the like.
 template <typename T>
 class PreParserList {
  public:
@@ skipping 752 matching lines @@
   return pre_parser_->factory()->NewCallNew(function, args, pos);
 }
 
 
 void PreParserTraits::ParseArrowFunctionFormalParameterList(
     PreParserFormalParameters* parameters,
     PreParserExpression params, const Scanner::Location& params_loc,
     Scanner::Location* duplicate_loc, bool* ok) {
   // TODO(wingo): Detect duplicated identifiers in paramlists.  Detect parameter
   // lists that are too long.
+
+  // Accomodate array literal for rest parameter.
+  if (params.HasRestParameter()) {
+    ++parameters->materialized_literals_count;
+    pre_parser_->function_state_->NextMaterializedLiteralIndex();
+  }
 }
 
 
 PreParserStatementList PreParser::ParseEagerFunctionBody(
     PreParserIdentifier function_name, int pos,
     const PreParserFormalParameters& parameters, FunctionKind kind,
     FunctionLiteral::FunctionType function_type, bool* ok) {
   ParsingModeScope parsing_mode(this, PARSE_EAGERLY);
 
   ParseStatementList(Token::RBRACE, ok);
@@ skipping 518 matching lines @@
   //   AssignmentExpression
   //   Expression ',' AssignmentExpression
 
   ExpressionClassifier binding_classifier;
   ExpressionT result =
       this->ParseAssignmentExpression(accept_IN, &binding_classifier, CHECK_OK);
   classifier->Accumulate(binding_classifier,
                          ExpressionClassifier::AllProductions);
   bool is_simple_parameter_list = this->IsIdentifier(result);
   bool seen_rest = false;
+
   while (peek() == Token::COMMA) {
     if (seen_rest) {
       // At this point the production can't possibly be valid, but we don't know
       // which error to signal.
       classifier->RecordArrowFormalParametersError(
           scanner()->peek_location(), MessageTemplate::kParamAfterRest);
     }
     Consume(Token::COMMA);
+    Token::Value next = peek();
+    Scanner::Location next_location = scanner()->peek_location();
     bool is_rest = false;
     if (allow_harmony_rest_parameters() && peek() == Token::ELLIPSIS) {
       // 'x, y, ...z' in CoverParenthesizedExpressionAndArrowParameterList only
       // as the formal parameters of'(x, y, ...z) => foo', and is not itself a
       // valid expression or binding pattern.
       ExpressionUnexpectedToken(classifier);
       BindingPatternUnexpectedToken(classifier);
       Consume(Token::ELLIPSIS);
       seen_rest = is_rest = true;
     }
     int pos = position();
     ExpressionT right = this->ParseAssignmentExpression(
         accept_IN, &binding_classifier, CHECK_OK);
-    if (is_rest) right = factory()->NewSpread(right, pos);
+    if (is_rest) {
+      if (!this->IsIdentifier(right)) {
+        ReportUnexpectedTokenAt(next_location, next);
+        *ok = false;
+        return this->EmptyExpression();
+      }
+      right = factory()->NewSpread(right, pos);
+    }
+
     is_simple_parameter_list =
         is_simple_parameter_list && this->IsIdentifier(right);
     classifier->Accumulate(binding_classifier,
                            ExpressionClassifier::AllProductions);
     result = factory()->NewBinaryOperation(Token::COMMA, result, right, pos);
   }
   if (!is_simple_parameter_list || seen_rest) {
     classifier->RecordNonSimpleParameter();
   }
   return result;
@@ skipping 428 matching lines @@
     ValidateArrowFormalParameters(&arrow_formals_classifier, expression,
                                   parenthesized_formals, CHECK_OK);
     Scanner::Location loc(lhs_beg_pos, scanner()->location().end_pos);
     Scope* scope =
         this->NewScope(scope_, ARROW_SCOPE, FunctionKind::kArrowFunction);
     FormalParametersT parameters(scope);
     if (!arrow_formals_classifier.is_simple_parameter_list()) {
       scope->SetHasNonSimpleParameters();
       parameters.is_simple = false;
     }
+
+    Scanner::Location duplicate_loc = Scanner::Location::invalid();
+    this->ParseArrowFunctionFormalParameterList(&parameters, expression, loc,
+                                                &duplicate_loc, CHECK_OK);
+
     checkpoint.Restore(&parameters.materialized_literals_count);
 
     scope->set_start_position(lhs_beg_pos);
-    Scanner::Location duplicate_loc = Scanner::Location::invalid();
-    this->ParseArrowFunctionFormalParameterList(&parameters, expression, loc,
-                                                &duplicate_loc, CHECK_OK);
     if (duplicate_loc.IsValid()) {
       arrow_formals_classifier.RecordDuplicateFormalParameterError(
           duplicate_loc);
     }
+
     expression = this->ParseArrowFunctionLiteral(
         parameters, arrow_formals_classifier, CHECK_OK);
     return expression;
   }
 
   // "expression" was not itself an arrow function parameter list, but it might
   // form part of one.  Propagate speculative formal parameter error locations.
   classifier->Accumulate(arrow_formals_classifier,
                          ExpressionClassifier::StandardProductions |
                              ExpressionClassifier::FormalParametersProductions);
@@ skipping 764 matching lines @@
       default:
         return expression;
     }
   }
   DCHECK(false);
   return this->EmptyExpression();
 }
 
 
 template <class Traits>
-void ParserBase<Traits>::ParseFormalParameter(
-    FormalParametersT* parameters, ExpressionClassifier* classifier, bool* ok) {
+void ParserBase<Traits>::ParseFormalParameter(FormalParametersT* parameters,
+                                              ExpressionClassifier* classifier,
+                                              bool* ok) {
   // FormalParameter[Yield,GeneratorParameter] :
   //   BindingElement[?Yield, ?GeneratorParameter]
   bool is_rest = parameters->has_rest;
 
   Token::Value next = peek();
   ExpressionT pattern = ParsePrimaryExpression(classifier, ok);
   if (!*ok) return;
 
   ValidateBindingPattern(classifier, ok);
   if (!*ok) return;
 
   if (!Traits::IsIdentifier(pattern)) {
     if (is_rest || !allow_harmony_destructuring()) {
       ReportUnexpectedToken(next);
       *ok = false;
       return;
     }
     parameters->is_simple = false;
     classifier->RecordNonSimpleParameter();
   }
 
+  if (is_rest) {
+    parameters->rest_array_literal_index =
+        function_state_->NextMaterializedLiteralIndex();
+    ++parameters->materialized_literals_count;
+  }
+
   ExpressionT initializer = Traits::EmptyExpression();
   if (!is_rest && allow_harmony_default_parameters() && Check(Token::ASSIGN)) {
     ExpressionClassifier init_classifier;
     initializer = ParseAssignmentExpression(true, &init_classifier, ok);
     if (!*ok) return;
     ValidateExpression(&init_classifier, ok);
     if (!*ok) return;
     parameters->is_simple = false;
     classifier->RecordNonSimpleParameter();
   }
@@ skipping 118 matching lines @@
 
     if (peek() == Token::LBRACE) {
       // Multiple statement body
       Consume(Token::LBRACE);
       bool is_lazily_parsed =
           (mode() == PARSE_LAZILY && scope_->AllowsLazyCompilation());
       if (is_lazily_parsed) {
         body = this->NewStatementList(0, zone());
         this->SkipLazyFunctionBody(&materialized_literal_count,
                                    &expected_property_count, CHECK_OK);
+
+        if (formal_parameters.materialized_literals_count > 0) {
+          materialized_literal_count +=
+              formal_parameters.materialized_literals_count;
+        }
       } else {
         body = this->ParseEagerFunctionBody(
             this->EmptyIdentifier(), RelocInfo::kNoPosition, formal_parameters,
             kArrowFunction, FunctionLiteral::ANONYMOUS_EXPRESSION, CHECK_OK);
         materialized_literal_count =
             function_state.materialized_literal_count();
         expected_property_count = function_state.expected_property_count();
       }
     } else {
       // Single-expression body
@@ skipping 246 matching lines @@
       *ok = false;
       return;
     }
     has_seen_constructor_ = true;
     return;
   }
 }
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H