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

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/base/platform/platform.h"
 #include "src/bootstrapper.h"
@@ skipping 1140 matching lines @@
   //    LetDeclaration
   //    ConstDeclaration
   //    ModuleDeclaration
   //    ImportDeclaration
   //    ExportDeclaration
   //    GeneratorDeclaration
 
   switch (peek()) {
     case Token::FUNCTION:
       return ParseFunctionDeclaration(NULL, ok);
-    case Token::LET:
-    case Token::CONST:
-      return ParseVariableStatement(kModuleElement, NULL, ok);
     case Token::IMPORT:
       return ParseImportDeclaration(ok);
     case Token::EXPORT:
       return ParseExportDeclaration(ok);
+    case Token::CONST:
+      return ParseVariableStatement(kModuleElement, NULL, ok);
+    case Token::LET:
+      if (allow_harmony_scoping() && strict_mode() == STRICT) {

[marja, 2014/07/09 14:24:45]

(See below; isn't allow_harmony_scoping() necessarily true here.)

+        return ParseVariableStatement(kModuleElement, NULL, ok);
+      }
+      // Fall through.
     default: {
       Statement* stmt = ParseStatement(labels, CHECK_OK);
       // Handle 'module' as a context-sensitive keyword.
       if (FLAG_harmony_modules &&
           peek() == Token::IDENTIFIER &&
           !scanner()->HasAnyLineTerminatorBeforeNext() &&
           stmt != NULL) {
         ExpressionStatement* estmt = stmt->AsExpressionStatement();
         if (estmt != NULL && estmt->expression()->AsVariableProxy() != NULL &&
             estmt->expression()->AsVariableProxy()->raw_name() ==
@@ skipping 278 matching lines @@
 Statement* Parser::ParseExportDeclaration(bool* ok) {
   // ExportDeclaration:
   //    'export' Identifier (',' Identifier)* ';'
   //    'export' VariableDeclaration
   //    'export' FunctionDeclaration
   //    'export' GeneratorDeclaration
   //    'export' ModuleDeclaration
   //
   // TODO(ES6): implement structuring ExportSpecifiers
 
+  ASSERT(strict_mode() == STRICT);
+
   Expect(Token::EXPORT, CHECK_OK);
 
   Statement* result = NULL;
   ZoneList<const AstRawString*> names(1, zone());
   switch (peek()) {
     case Token::IDENTIFIER: {
       int pos = position();
       const AstRawString* name =
           ParseIdentifier(kDontAllowEvalOrArguments, CHECK_OK);
       // Handle 'module' as a context-sensitive keyword.
@@ skipping 62 matching lines @@
   //
   // In harmony mode we allow additionally the following productions
   // BlockElement (aka SourceElement):
   //    LetDeclaration
   //    ConstDeclaration
   //    GeneratorDeclaration
 
   switch (peek()) {
     case Token::FUNCTION:
       return ParseFunctionDeclaration(NULL, ok);
-    case Token::LET:
     case Token::CONST:
       return ParseVariableStatement(kModuleElement, NULL, ok);
+    case Token::LET:
+      if (allow_harmony_scoping() && strict_mode() == STRICT) {

[marja, 2014/07/09 14:24:45]

Ditto

+        return ParseVariableStatement(kModuleElement, NULL, ok);
+      }
+      // Fall through.
     default:
       return ParseStatement(labels, ok);
   }
 }
 
 
 Statement* Parser::ParseStatement(ZoneList<const AstRawString*>* labels,
                                   bool* ok) {
   // Statement ::
   //   Block
@@ skipping 15 matching lines @@
   // Note: Since labels can only be used by 'break' and 'continue'
   // statements, which themselves are only valid within blocks,
   // 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.
   switch (peek()) {
     case Token::LBRACE:
       return ParseBlock(labels, ok);
 
-    case Token::CONST:  // fall through
-    case Token::LET:
-    case Token::VAR:
-      return ParseVariableStatement(kStatement, NULL, ok);
-
     case Token::SEMICOLON:
       Next();
       return factory()->NewEmptyStatement(RelocInfo::kNoPosition);
 
     case Token::IF:
       return ParseIfStatement(labels, ok);
 
     case Token::DO:
       return ParseDoWhileStatement(labels, ok);
 
@@ skipping 51 matching lines @@
         ReportMessageAt(scanner()->peek_location(), "strict_function");
         *ok = false;
         return NULL;
       }
       return ParseFunctionDeclaration(NULL, ok);
     }
 
     case Token::DEBUGGER:
       return ParseDebuggerStatement(ok);
 
+    case Token::VAR:
+    case Token::CONST:
+      return ParseVariableStatement(kStatement, NULL, ok);
+
+    case Token::LET:
+      if (allow_harmony_scoping() && strict_mode() == STRICT) {

[marja, 2014/07/09 14:24:45]

I don't think we need to check allow_harmony_scoping() here; if it's not
allowed, we don't get Token::LET. Also, below you don't check it either.

[rossberg, 2014/07/09 14:28:50]

Yes, this was on purpose -- I wanted to be able to grep for harmony-scoping
specific code paths easily. But I can remove that if you prefer.

+        return ParseVariableStatement(kStatement, NULL, ok);
+      }
+      // Fall through.
     default:
       return ParseExpressionOrLabelledStatement(labels, ok);
   }
 }
 
 
 VariableProxy* Parser::NewUnresolved(const AstRawString* name,
                                      VariableMode mode, Interface* interface) {
   // If we are inside a function, a declaration of a var/const variable is a
   // truly local variable, and the scope of the variable is always the function
@@ skipping 383 matching lines @@
           mode = CONST;
           init_op = Token::INIT_CONST;
         } else {
           ReportMessage("strict_const");
           *ok = false;
           return NULL;
         }
     }
     is_const = true;
     needs_init = true;
-  } 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) {
-      ReportMessage("illegal_let");
-      *ok = false;
-      return NULL;
-    }
+  } else if (peek() == Token::LET && strict_mode() == STRICT) {
     Consume(Token::LET);
     if (var_context == kStatement) {
       // Let declarations are only allowed in source element positions.
       ReportMessage("unprotected_let");
       *ok = false;
       return NULL;
     }
     mode = LET;
     needs_init = true;
     init_op = Token::INIT_LET;
@@ skipping 1018 matching lines @@
         result->AddStatement(loop, zone());
         scope_ = saved_scope;
         for_scope->set_end_position(scanner()->location().end_pos);
         for_scope = for_scope->FinalizeBlockScope();
         ASSERT(for_scope == NULL);
         // Parsed for-in loop w/ variable/const declaration.
         return result;
       } else {
         init = variable_statement;
       }
-    } else if (peek() == Token::LET) {
+    } else if (peek() == Token::LET && strict_mode() == STRICT) {
       const AstRawString* name = NULL;
       VariableDeclarationProperties decl_props = kHasNoInitializers;
       Block* variable_statement =
           ParseVariableDeclarations(kForStatement, &decl_props, &let_bindings,
                                     &name, CHECK_OK);
       bool accept_IN = name != NULL && decl_props != kHasInitializers;
       bool accept_OF = decl_props == kHasNoInitializers;
       ForEachStatement::VisitMode mode;
 
       if (accept_IN && CheckInOrOf(accept_OF, &mode)) {
@@ skipping 1758 matching lines @@
     info()->SetAstValueFactory(ast_value_factory_);
   }
   ast_value_factory_ = NULL;
 
   InternalizeUseCounts();
 
   return (result != NULL);
 }
 
 } }  // namespace v8::internal