Make `let` usable as an identifier in ES6 sloppy mode.

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 "include/v8stdint.h"
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
@@ skipping 43 matching lines @@
                                 is_reference_error);
 }
 
 
 PreParserIdentifier PreParserTraits::GetSymbol(Scanner* scanner) {
   if (scanner->current_token() == Token::FUTURE_RESERVED_WORD) {
     return PreParserIdentifier::FutureReserved();
   } else if (scanner->current_token() ==
              Token::FUTURE_STRICT_RESERVED_WORD) {
     return PreParserIdentifier::FutureStrictReserved();
+  } else if (scanner->current_token() == Token::LET) {
+    return PreParserIdentifier::Let();
   } else if (scanner->current_token() == Token::YIELD) {
     return PreParserIdentifier::Yield();
   }
   if (scanner->UnescapedLiteralMatches("eval", 4)) {
     return PreParserIdentifier::Eval();
   }
   if (scanner->UnescapedLiteralMatches("arguments", 9)) {
     return PreParserIdentifier::Arguments();
   }
   return PreParserIdentifier::Default();
@@ skipping 86 matching lines @@
   //
   // In harmony mode we allow additionally the following productions
   // SourceElement:
   //    LetDeclaration
   //    ConstDeclaration
   //    GeneratorDeclaration
 
   switch (peek()) {
     case Token::FUNCTION:
       return ParseFunctionDeclaration(ok);
-    case Token::LET:
     case Token::CONST:
       return ParseVariableStatement(kSourceElement, ok);
+    case Token::LET:
+      ASSERT(allow_harmony_scoping());
+      if (strict_mode() == STRICT) {
+        return ParseVariableStatement(kSourceElement, ok);
+      }
+      // Fall through.
     default:
       return ParseStatement(ok);
   }
 }
 
 
 PreParser::SourceElements PreParser::ParseSourceElements(int end_token,
                                                          bool* ok) {
   // SourceElements ::
   //   (Statement)* <end_token>
@@ skipping 47 matching lines @@
   // iterations or 'switch' statements (i.e., BreakableStatements),
   // labels can be simply ignored in all other cases; except for
   // trivial labeled break statements 'label: break label' which is
   // parsed into an empty statement.
 
   // Keep the source position of the statement
   switch (peek()) {
     case Token::LBRACE:
       return ParseBlock(ok);
 
-    case Token::CONST:
-    case Token::LET:
-    case Token::VAR:
-      return ParseVariableStatement(kStatement, ok);
-
     case Token::SEMICOLON:
       Next();
       return Statement::Default();
 
     case Token::IF:
       return ParseIfStatement(ok);
 
     case Token::DO:
       return ParseDoWhileStatement(ok);
 
@@ skipping 35 matching lines @@
         *ok = false;
         return Statement::Default();
       } else {
         return statement;
       }
     }
 
     case Token::DEBUGGER:
       return ParseDebuggerStatement(ok);
 
+    case Token::VAR:
+    case Token::CONST:
+      return ParseVariableStatement(kStatement, ok);
+
+    case Token::LET:
+      ASSERT(allow_harmony_scoping());
+      if (strict_mode() == STRICT) {
+        return ParseVariableStatement(kStatement, ok);
+      }
+      // Fall through.
     default:
       return ParseExpressionOrLabelledStatement(ok);
   }
 }
 
 
 PreParser::Statement PreParser::ParseFunctionDeclaration(bool* ok) {
   // FunctionDeclaration ::
   //   'function' Identifier '(' FormalParameterListopt ')' '{' FunctionBody '}'
   // GeneratorDeclaration ::
@@ skipping 98 matching lines @@
           return Statement::Default();
         }
         require_initializer = true;
       } else {
         Scanner::Location location = scanner()->peek_location();
         ReportMessageAt(location, "strict_const");
         *ok = false;
         return Statement::Default();
       }
     }
-  } else if (peek() == Token::LET) {
-    // ES6 Draft Rev4 section 12.2.1:
-    //
-    // LetDeclaration : let LetBindingList ;
-    //
-    // * It is a Syntax Error if the code that matches this production is not
-    //   contained in extended code.
-    //
-    // TODO(rossberg): make 'let' a legal identifier in sloppy mode.
-    if (!allow_harmony_scoping() || strict_mode() == SLOPPY) {
-      ReportMessageAt(scanner()->peek_location(), "illegal_let");
-      *ok = false;
-      return Statement::Default();
-    }
+  } else if (peek() == Token::LET && strict_mode() == STRICT) {
     Consume(Token::LET);
-    if (var_context != kSourceElement &&
-        var_context != kForStatement) {
+    if (var_context != kSourceElement && var_context != kForStatement) {
       ReportMessageAt(scanner()->peek_location(), "unprotected_let");
       *ok = false;
       return Statement::Default();
     }
   } else {
     *ok = false;
     return Statement::Default();
   }
 
   // The scope of a var/const declared variable anywhere inside a function
@@ skipping 217 matching lines @@
 
 
 PreParser::Statement PreParser::ParseForStatement(bool* ok) {
   // ForStatement ::
   //   'for' '(' Expression? ';' Expression? ';' Expression? ')' Statement
 
   Expect(Token::FOR, CHECK_OK);
   Expect(Token::LPAREN, CHECK_OK);
   if (peek() != Token::SEMICOLON) {
     if (peek() == Token::VAR || peek() == Token::CONST ||
-        peek() == Token::LET) {
+        (peek() == Token::LET && strict_mode() == STRICT)) {
       bool is_let = peek() == Token::LET;
       int decl_count;
       VariableDeclarationProperties decl_props = kHasNoInitializers;
       ParseVariableDeclarations(
           kForStatement, &decl_props, &decl_count, CHECK_OK);
       bool has_initializers = decl_props == kHasInitializers;
       bool accept_IN = decl_count == 1 && !(is_let && has_initializers);
       bool accept_OF = !has_initializers;
       if (accept_IN && CheckInOrOf(accept_OF)) {
         ParseExpression(true, CHECK_OK);
@@ skipping 244 matching lines @@
   ParseIdentifier(kAllowEvalOrArguments, CHECK_OK);
   ParseArguments(ok);
 
   return Expression::Default();
 }
 
 #undef CHECK_OK
 
 
 } }  // v8::internal