[parser] early error when declaration Pattern missing Initializer

src/preparser.cc

 // Copyright 2011 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 <cmath>
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
 #include "src/conversions-inl.h"
 #include "src/conversions.h"
@@ skipping 514 matching lines @@
   //
   // ConstDeclaration ::
   //   const ConstBinding (',' ConstBinding)* ';'
   // ConstBinding ::
   //   Identifier '=' AssignmentExpression
   //
   // TODO(ES6):
   // ConstBinding ::
   //   BindingPattern '=' AssignmentExpression
   bool require_initializer = false;
-  bool is_strict_const = false;
   bool lexical = false;
   if (peek() == Token::VAR) {
     if (is_strong(language_mode())) {
       Scanner::Location location = scanner()->peek_location();
       ReportMessageAt(location, MessageTemplate::kStrongVar);
       *ok = false;
       return Statement::Default();
     }
     Consume(Token::VAR);
   } else if (peek() == Token::CONST && allow_const()) {
     // TODO(ES6): The ES6 Draft Rev4 section 12.2.2 reads:
     //
     // ConstDeclaration : const ConstBinding (',' ConstBinding)* ';'
     //
     // * It is a Syntax Error if the code that matches this production is not
     //   contained in extended code.
     //
     // However disallowing const in sloppy mode will break compatibility with
     // existing pages. Therefore we keep allowing const with the old
     // non-harmony semantics in sloppy mode.
     Consume(Token::CONST);
     if (is_strict(language_mode()) ||
         (allow_harmony_sloppy() && !allow_legacy_const())) {
       DCHECK(var_context != kStatement);
-      is_strict_const = true;
-      require_initializer = var_context != kForStatement;
+      require_initializer = true;
       lexical = true;
     }
   } else if (peek() == Token::LET && allow_let()) {
     Consume(Token::LET);
     DCHECK(var_context != kStatement);
     lexical = true;
   } else {
     *ok = false;
     return Statement::Default();
   }
 
   // The scope of a var/const declared variable anywhere inside a function
   // is the entire function (ECMA-262, 3rd, 10.1.3, and 12.2). The scope
   // of a let declared variable is the scope of the immediately enclosing
   // block.
   int nvars = 0;  // the number of variables declared
   int bindings_start = peek_position();
   do {
     // Parse binding pattern.
     if (nvars > 0) Consume(Token::COMMA);
+    int decl_pos = peek_position();
+    PreParserExpression pattern = PreParserExpression::Default();
     {
       ExpressionClassifier pattern_classifier;
       Token::Value next = peek();
-      PreParserExpression pattern =
-          ParsePrimaryExpression(&pattern_classifier, CHECK_OK);
+      pattern = ParsePrimaryExpression(&pattern_classifier, CHECK_OK);
+
       ValidateBindingPattern(&pattern_classifier, CHECK_OK);
       if (lexical) {
         ValidateLetPattern(&pattern_classifier, CHECK_OK);
       }
 
       if (!allow_harmony_destructuring() && !pattern.IsIdentifier()) {
         ReportUnexpectedToken(next);
         *ok = false;
         return Statement::Default();
       }
     }
 
+    bool is_pattern = pattern.IsObjectLiteral() || pattern.IsArrayLiteral();
+
+    bool is_for_iteration_variable =
+        var_context == kForStatement &&
+        (peek() == Token::IN || PeekContextualKeyword(CStrVector("of")));
+
     Scanner::Location variable_loc = scanner()->location();
     nvars++;
-    if (peek() == Token::ASSIGN || require_initializer ||
-        // require initializers for multiple consts.
-        (is_strict_const && peek() == Token::COMMA)) {
-      Expect(Token::ASSIGN, CHECK_OK);
+    if (Check(Token::ASSIGN)) {
       ExpressionClassifier classifier;
       ParseAssignmentExpression(var_context != kForStatement, &classifier,
                                 CHECK_OK);
       ValidateExpression(&classifier, CHECK_OK);
 
       variable_loc.end_pos = scanner()->location().end_pos;
       if (first_initializer_loc && !first_initializer_loc->IsValid()) {
         *first_initializer_loc = variable_loc;
       }
+    } else if ((require_initializer || is_pattern) &&
+               !is_for_iteration_variable) {
+      PreParserTraits::ReportMessageAt(
+          Scanner::Location(decl_pos, scanner()->location().end_pos),
+          MessageTemplate::kDeclarationMissingInitializer,
+          is_pattern ? "destructuring" : "const");
+      *ok = false;
+      return Statement::Default();
     }
   } while (peek() == Token::COMMA);
 
   if (bindings_loc) {
     *bindings_loc =
         Scanner::Location(bindings_start, scanner()->location().end_pos);
   }
 
   if (num_decl != NULL) *num_decl = nvars;
   return Statement::Default();
@@ skipping 630 matching lines @@
     Expect(Token::RBRACE, CHECK_OK);
     return PreParserExpression::Default();
   }
 }
 
 #undef CHECK_OK
 
 
 }  // namespace internal
 }  // namespace v8