Parse harmony let declarations.

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 1167f43df519321d34a8a7efad9e085b2af7e548..6886340ef5f8b5612eb92575c6be7e2773d9f93a 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -1093,6 +1093,25 @@ class ThisNamedPropertyAssigmentFinder : public ParserFinder {
 };
 
 
+Statement* Parser::ParseSourceElement(ZoneStringList* labels,
+                                      bool* ok) {
+  if (peek() == Token::FUNCTION) {
+    // FunctionDeclaration is only allowed in the context of SourceElements
+    // (Ecma 262 5th Edition, clause 14):
+    // SourceElement:
+    //    Statement
+    //    FunctionDeclaration
+    // Common language extension is to allow function declaration in place
+    // of any statement. This language extension is disabled in strict mode.
+    return ParseFunctionDeclaration(ok);
+  } else if (peek() == Token::LET && harmony_block_scoping_) {
+    return ParseVariableStatement(true, ok);

[Lasse Reichstein, 2011/08/12 08:08:33]

Please use an enum with meaningful names for the first argument. Generally try
to avoid passing booleans as true/false (or other magical constants).

[Steven, 2011/08/16 09:05:32]

Done. See the VariableDeclarationContext enum. Also removed the accept_IN from
ParseVariableDeclarations.

On 2011/08/12 08:08:33, Lasse Reichstein wrote:

+  } else {
+    return ParseStatement(labels, ok);
+  }
+}
+
+
 void* Parser::ParseSourceElements(ZoneList<Statement*>* processor,
                                   int end_token,
                                   bool* ok) {
@@ -1116,21 +1135,7 @@ void* Parser::ParseSourceElements(ZoneList<Statement*>* processor,
     }
 
     Scanner::Location token_loc = scanner().peek_location();
-
-    Statement* stat;
-    if (peek() == Token::FUNCTION) {
-      // FunctionDeclaration is only allowed in the context of SourceElements
-      // (Ecma 262 5th Edition, clause 14):
-      // SourceElement:
-      //    Statement
-      //    FunctionDeclaration
-      // Common language extension is to allow function declaration in place
-      // of any statement. This language extension is disabled in strict mode.
-      stat = ParseFunctionDeclaration(CHECK_OK);
-    } else {
-      stat = ParseStatement(NULL, CHECK_OK);
-    }
-
+    Statement* stat = ParseSourceElement(NULL, CHECK_OK);
     if (stat == NULL || stat->IsEmpty()) {
       directive_prologue = false;   // End of directive prologue.
       continue;
@@ -1218,7 +1223,7 @@ Statement* Parser::ParseStatement(ZoneStringList* labels, bool* ok) {
 
     case Token::CONST:  // fall through
     case Token::VAR:
-      stmt = ParseVariableStatement(ok);
+      stmt = ParseVariableStatement(false, ok);
       break;
 
     case Token::SEMICOLON:
@@ -1325,24 +1330,28 @@ VariableProxy* Parser::Declare(Handle<String> name,
   // to the calling function context.
   // Similarly, strict mode eval scope does not leak variable declarations to
   // the caller's scope so we declare all locals, too.
-  Scope* declaration_scope = top_scope_->DeclarationScope();
+
+  Scope* declaration_scope = mode == Variable::LET ? top_scope_
+      : top_scope_->DeclarationScope();
   if (declaration_scope->is_function_scope() ||
-      declaration_scope->is_strict_mode_eval_scope()) {
+      declaration_scope->is_strict_mode_eval_scope() ||
+      declaration_scope->is_block_scope()) {
     // Declare the variable in the function scope.
     var = declaration_scope->LocalLookup(name);
     if (var == NULL) {
       // Declare the name.
       var = declaration_scope->DeclareLocal(name, mode);
     } else {
-      // The name was declared before; check for conflicting
-      // re-declarations. If the previous declaration was a const or the
-      // current declaration is a const then we have a conflict. There is
-      // similar code in runtime.cc in the Declare functions.
-      if ((mode == Variable::CONST) || (var->mode() == Variable::CONST)) {
-        // We only have vars and consts in declarations.
+      // The name was declared before; check for conflicting re-declarations.
+      // We have a conflict if either of the declarations is not a var. There
+      // is similar code in runtime.cc in the Declare functions.
+      if ((mode != Variable::VAR) || (var->mode() != Variable::VAR)) {
+        // We only have vars, consts and lets in declarations.
         ASSERT(var->mode() == Variable::VAR ||
-               var->mode() == Variable::CONST);
-        const char* type = (var->mode() == Variable::VAR) ? "var" : "const";
+               var->mode() == Variable::CONST ||
+               var->mode() == Variable::LET);
+        const char* type = (var->mode() == Variable::VAR) ? "var" :
+                           (var->mode() == Variable::CONST) ? "const" : "let";
         Handle<String> type_string =
             isolate()->factory()->NewStringFromUtf8(CStrVector(type), TENURED);
         Expression* expression =
@@ -1485,7 +1494,8 @@ Statement* Parser::ParseFunctionDeclaration(bool* ok) {
   // Even if we're not at the top-level of the global or a function
   // scope, we treat is as such and introduce the function with it's
   // initial value upon entering the corresponding scope.
-  Declare(name, Variable::VAR, fun, true, CHECK_OK);
+  Variable::Mode mode = harmony_block_scoping_ ? Variable::LET : Variable::VAR;
+  Declare(name, mode, fun, true, CHECK_OK);
   return EmptyStatement();
 }
 
@@ -1540,7 +1550,7 @@ Block* Parser::ParseScopedBlock(ZoneStringList* labels, bool* ok) {
     InitializationBlockFinder block_finder(top_scope_, target_stack_);
 
     while (peek() != Token::RBRACE) {
-      Statement* stat = ParseStatement(NULL, CHECK_OK);
+      Statement* stat = ParseSourceElement(NULL, CHECK_OK);

[Lasse Reichstein, 2011/08/12 08:08:33]

Will this enable function declarations inside blocks in strict mode? It's
allowed as a SourceElement but not as a Statement.

[Steven, 2011/08/16 09:05:32]

The proposal allows local function declarations inside blocks, but they
shouldn't be allowed in a statement context that is not a source element
context. This function is not used in ES5 normal or strict mode.
On 2011/08/12 08:08:33, Lasse Reichstein wrote:

       if (stat && !stat->IsEmpty()) {
         body->AddStatement(stat);
         block_finder.Update(stat);
@@ -1566,12 +1576,13 @@ Block* Parser::ParseScopedBlock(ZoneStringList* labels, bool* ok) {
 }
 
 
-Block* Parser::ParseVariableStatement(bool* ok) {
+Block* Parser::ParseVariableStatement(bool accept_LET, bool* ok) {
   // VariableStatement ::
   //   VariableDeclarations ';'
 
   Handle<String> ignore;
-  Block* result = ParseVariableDeclarations(true, &ignore, CHECK_OK);
+  Block* result = ParseVariableDeclarations(accept_LET, true,
+                                            &ignore, CHECK_OK);
   ExpectSemicolon(CHECK_OK);
   return result;
 }
@@ -1588,7 +1599,8 @@ bool Parser::IsEvalOrArguments(Handle<String> string) {
 // *var is untouched; in particular, it is the caller's responsibility
 // to initialize it properly. This mechanism is used for the parsing
 // of 'for-in' loops.
-Block* Parser::ParseVariableDeclarations(bool accept_IN,
+Block* Parser::ParseVariableDeclarations(bool accept_LET,
+                                         bool accept_IN,
                                          Handle<String>* out,
                                          bool* ok) {
   // VariableDeclarations ::
@@ -1608,6 +1620,14 @@ Block* Parser::ParseVariableDeclarations(bool accept_IN,
     }
     mode = Variable::CONST;
     is_const = true;
+  } else if (peek() == Token::LET) {
+    Consume(Token::LET);
+    if (!accept_LET) {
+      ReportMessage("unprotected_let", Vector<const char*>::empty());
+      *ok = false;
+      return NULL;
+    }
+    mode = Variable::LET;
   } else {
     UNREACHABLE();  // by current callers
   }
@@ -2346,7 +2366,7 @@ Statement* Parser::ParseForStatement(ZoneStringList* labels, bool* ok) {
     if (peek() == Token::VAR || peek() == Token::CONST) {
       Handle<String> name;
       Block* variable_statement =
-          ParseVariableDeclarations(false, &name, CHECK_OK);
+          ParseVariableDeclarations(true, false, &name, CHECK_OK);
 
       if (peek() == Token::IN && !name.is_null()) {
         VariableProxy* each = top_scope_->NewUnresolved(name, inside_with());
@@ -2993,6 +3013,14 @@ void Parser::ReportUnexpectedToken(Token::Value token) {
     case Token::FUTURE_RESERVED_WORD:
       return ReportMessage("unexpected_reserved",
                            Vector<const char*>::empty());
+    case Token::LET:
+      if (harmony_block_scoping_) {
+        const char* name = Token::String(token);
+        ASSERT(name != NULL);
+        return ReportMessage("unexpected_token",
+                             Vector<const char*>(&name, 1));
+      }
+      // FALLTHROUGH
     case Token::FUTURE_STRICT_RESERVED_WORD:
       return ReportMessage(top_scope_->is_strict_mode() ?
                                "unexpected_strict_reserved" :
@@ -3055,6 +3083,14 @@ Expression* Parser::ParsePrimaryExpression(bool* ok) {
           isolate(), isolate()->factory()->false_value());
       break;
 
+    case Token::LET:
+      if (harmony_block_scoping_) {
+        Token::Value tok = Next();
+        ReportUnexpectedToken(tok);
+        *ok = false;
+        return NULL;
+      }
+      // FALLTHROUGH
     case Token::IDENTIFIER:
     case Token::FUTURE_STRICT_RESERVED_WORD: {
       Handle<String> name = ParseIdentifier(CHECK_OK);
@@ -3519,6 +3555,12 @@ Expression* Parser::ParseObjectLiteral(bool* ok) {
     // Location of the property name token
     Scanner::Location loc = scanner().peek_location();
 
+    if (harmony_block_scoping_ && next == Token::LET) {
+      // Go into FUTURE_STRICT_RESERVED_WORD case where
+      // ParseIdentifierNameOrGetOrSet will handle the LET
+      // token like a FUTURE_STRICT_RESERVED_WORD.
+      next = Token::FUTURE_STRICT_RESERVED_WORD;

[Lasse Reichstein, 2011/08/12 08:08:33]

Why not just add a case for Token::LET next to
Token::FUTURE_STRICT_RESERVED_WORD?
Or not bother, and let it be handled like a keyword? 
Both should work.

[Steven, 2011/08/16 09:05:32]

Now obsolete, since the scanner now produces the correct token based on a flag.
On 2011/08/12 08:08:33, Lasse Reichstein wrote:

+    }
     switch (next) {
       case Token::FUTURE_RESERVED_WORD:
       case Token::FUTURE_STRICT_RESERVED_WORD:
@@ -3706,7 +3748,8 @@ FunctionLiteral* Parser::ParseFunctionLiteral(Handle<String> function_name,
 
   int num_parameters = 0;
   // Function declarations are hoisted.
-  Scope* scope = (type == FunctionLiteral::DECLARATION)
+  Scope* scope = (type == FunctionLiteral::DECLARATION &&
+                  !harmony_block_scoping_)

[Lasse Reichstein, 2011/08/12 08:08:33]

If harmony_block_scoping_ is set, function declarations are not hoisted?

[Steven, 2011/08/16 09:05:32]

Yes, function declarations are then also expected to be block scoped.
On 2011/08/12 08:08:33, Lasse Reichstein wrote:

       ? NewScope(top_scope_->DeclarationScope(), Scope::FUNCTION_SCOPE, false)
       : NewScope(top_scope_, Scope::FUNCTION_SCOPE, inside_with());
   ZoneList<Statement*>* body = new(zone()) ZoneList<Statement*>(8);
@@ -3946,7 +3989,8 @@ bool Parser::peek_any_identifier() {
   Token::Value next = peek();
   return next == Token::IDENTIFIER ||
          next == Token::FUTURE_RESERVED_WORD ||
-         next == Token::FUTURE_STRICT_RESERVED_WORD;
+         next == Token::FUTURE_STRICT_RESERVED_WORD ||
+         (next == Token::LET && !harmony_block_scoping_);
 }
 
 
@@ -4014,7 +4058,11 @@ Handle<String> Parser::ParseIdentifier(bool* ok) {
   if (top_scope_->is_strict_mode()) {
     Expect(Token::IDENTIFIER, ok);
   } else if (!Check(Token::IDENTIFIER)) {
-    Expect(Token::FUTURE_STRICT_RESERVED_WORD, ok);
+    if (harmony_block_scoping_) {
+      Expect(Token::FUTURE_STRICT_RESERVED_WORD, ok);
+    } else if (!Check(Token::FUTURE_STRICT_RESERVED_WORD)) {
+      Expect(Token::LET, ok);
+    }
   }
   if (!*ok) return Handle<String>();
   return GetSymbol(ok);
@@ -4027,7 +4075,11 @@ Handle<String> Parser::ParseIdentifierOrStrictReservedWord(
     bool* is_strict_reserved, bool* ok) {
   *is_strict_reserved = false;
   if (!Check(Token::IDENTIFIER)) {
-    Expect(Token::FUTURE_STRICT_RESERVED_WORD, ok);
+    if (harmony_block_scoping_) {
+      Expect(Token::FUTURE_STRICT_RESERVED_WORD, ok);
+    } else if (!Check(Token::FUTURE_STRICT_RESERVED_WORD)) {
+      Expect(Token::LET, ok);
+    }
     *is_strict_reserved = true;
   }
   if (!*ok) return Handle<String>();