Block scoped const variables.

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index edd2e531d439b16327afe1ca84952a0165b5a0c1..c391ca7acc7b7aba67e52f669e8f288cc348278d 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -1141,14 +1141,16 @@ Statement* Parser::ParseSourceElement(ZoneStringList* labels,
   // In harmony mode we allow additionally the following productions
   // SourceElement:
   //    LetDeclaration
+  //    ConstDeclaration
 
   if (peek() == Token::FUNCTION) {
     return ParseFunctionDeclaration(ok);
   } else if (peek() == Token::LET) {
     return ParseVariableStatement(kSourceElement, ok);
-  } else {
-    return ParseStatement(labels, ok);
+  } else if (peek() == Token::CONST && harmony_scoping_) {
+    return ParseHarmonyConstDeclaration(ok);
   }
+  return ParseStatement(labels, ok);
 }
 
 
@@ -1366,6 +1368,10 @@ VariableProxy* Parser::Declare(Handle<String> name,
   // 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
   // scope.
+  // Let/const variables in harmony mode are always added to the immediately
+  // enclosing scope.
+  Scope* declaration_scope = mode == LET || mode == CONST_HARMONY
+      ? top_scope_ : top_scope_->DeclarationScope();
 
   // If a function scope exists, then we can statically declare this
   // variable and also set its mode. In any case, a Declaration node
@@ -1375,9 +1381,8 @@ 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 = mode == LET ? top_scope_
-      : top_scope_->DeclarationScope();
+  // Also for block scoped let/const bindings the variable can be
+  // statically declared.
   if (declaration_scope->is_function_scope() ||
       declaration_scope->is_strict_mode_eval_scope() ||
       declaration_scope->is_block_scope()) {
@@ -1402,6 +1407,7 @@ VariableProxy* Parser::Declare(Handle<String> name,
         // We only have vars, consts and lets in declarations.
         ASSERT(var->mode() == VAR ||
                var->mode() == CONST ||
+               var->mode() == CONST_HARMONY ||
                var->mode() == LET);
         if (harmony_scoping_) {
           // In harmony mode we treat re-declarations as early errors. See
@@ -1413,8 +1419,8 @@ VariableProxy* Parser::Declare(Handle<String> name,
           *ok = false;
           return NULL;
         }
-        const char* type = (var->mode() == VAR) ? "var" :
-                           (var->mode() == CONST) ? "const" : "let";
+        const char* type = (var->mode() == VAR)
+            ? "var" : var->is_const_mode() ? "const" : "let";
         Handle<String> type_string =
             isolate()->factory()->NewStringFromUtf8(CStrVector(type), TENURED);
         Expression* expression =
@@ -1447,7 +1453,8 @@ VariableProxy* Parser::Declare(Handle<String> name,
       new(zone()) Declaration(proxy, mode, fun, top_scope_));
 
   // For global const variables we bind the proxy to a variable.
-  if (mode == CONST && declaration_scope->is_global_scope()) {
+  if ((mode == CONST || mode == CONST_HARMONY) &&
+      declaration_scope->is_global_scope()) {
     ASSERT(resolve);  // should be set by all callers
     Variable::Kind kind = Variable::NORMAL;
     var = new(zone()) Variable(declaration_scope, name, CONST, true, kind);
@@ -1645,6 +1652,114 @@ bool Parser::IsEvalOrArguments(Handle<String> string) {
 }
 
 
+Block* Parser::ParseHarmonyConstDeclaration(bool* ok) {
+  // ES6 Draft Rev3
+  //
+  // ConstDeclaration ::
+  //   const ConstBinding (',' ConstBinding)* ';'
+  // ConstBinding ::
+  //   Identifier '=' AssignmentExpression
+  //
+  // TODO(ES6):
+  // ConstBinding ::
+  //   BindingPattern '=' AssignmentExpression
+
+  Consume(Token::CONST);
+
+  // A block is used to collect the initialization assignments and it
+  // is marked as an initializer block to prevent the rewriter from
+  // adding a '.result' assignment to such a block.
+  //
+  // Create new block with one expected declaration.
+  Block* block = new(zone()) Block(isolate(), NULL, 1, true);
+  Handle<String> name;
+  do {
+    if (fni_ != NULL) fni_->Enter();
+
+    // Parse variable name.
+    name = ParseIdentifier(CHECK_OK);
+    if (fni_ != NULL) fni_->PushVariableName(name);
+
+    // Strict mode variables may not be named eval or arguments
+    if (IsEvalOrArguments(name)) {
+      ReportMessage("strict_var_name", Vector<const char*>::empty());
+      *ok = false;
+      return NULL;
+    }
+
+    // Declare the variable. The proxy can always be pre-resolved to the
+    // declared variable, because it resides in the same scope as the
+    // declaration.
+    VariableProxy* proxy = Declare(name, CONST_HARMONY, NULL, true, CHECK_OK);
+    if (top_scope_->num_var_or_const() > kMaxNumFunctionLocals) {

[fschneider, 2011/10/21 09:19:40]

This function contains a lot of duplicated code. Can you arrange it so to avoid
duplication where possible?

[Steven, 2011/10/24 09:37:55]

Done. Was actually easier than I thought to add it to ParseVariableDeclarations.

On 2011/10/21 09:19:40, fschneider wrote:

+      ReportMessageAt(scanner().location(), "too_many_variables",
+                      Vector<const char*>::empty());
+      *ok = false;
+      return NULL;
+    }
+
+    // Parse initialiser.
+    Expression* value = NULL;
+    Expect(Token::ASSIGN, CHECK_OK);
+    int position = scanner().location().beg_pos;
+    value = ParseAssignmentExpression(false, CHECK_OK);
+
+    // Don't infer if it is "a = function(){...}();"-like expression.
+    if (fni_ != NULL && value->AsCall() == NULL && value->AsCallNew() == NULL) {
+      fni_->Infer();
+    }
+
+    // Global variable declarations must be compiled in a specific
+    // way. When the script containing the global variable declaration
+    // is entered, the global variable must be declared, so that if it
+    // doesn't exist (not even in a prototype of the global object) it
+    // gets created with an initial undefined value. This is handled
+    // by the declarations part of the function representing the
+    // top-level global code; see Runtime::DeclareGlobals. If
+    // it already exists (in the object or in a prototype), it is
+    // *not* touched until the variable declaration statement is
+    // executed.
+    //
+    // Executing the variable declaration statement will always
+    // guarantee to give the global object a "local" variable; a
+    // variable defined in the global object and not in any
+    // prototype. This way, global variable declarations can shadow
+    // properties in the prototype chain, but only after the variable
+    // declaration statement has been executed. This is important in
+    // browsers where the global object (window) has lots of
+    // properties defined in prototype objects.
+    if (top_scope_->is_global_scope()) {
+      // Compute the arguments for the runtime call.
+      ZoneList<Expression*>* arguments = new(zone()) ZoneList<Expression*>(3);
+      // We have at least 1 parameter.
+      arguments->Add(NewLiteral(name));
+      arguments->Add(value);
+
+      // Construct the call to Runtime_InitializeConstGlobal
+      // and add it to the initialization statement block.
+      CallRuntime* initialize =
+          new(zone()) CallRuntime(
+              isolate(),
+              isolate()->factory()->InitializeConstGlobal_symbol(),
+              Runtime::FunctionForId(Runtime::kInitializeConstGlobal),
+              arguments);
+
+      block->AddStatement(new(zone()) ExpressionStatement(initialize));
+    } else {
+      // Add an assignment node for the initializations to the initialization
+      // statement block.
+      Assignment* assignment = new(zone()) Assignment(
+          isolate(), Token::INIT_CONST_HARMONY, proxy, value, position);
+      block->AddStatement(new(zone()) ExpressionStatement(assignment));
+    }
+    if (fni_ != NULL) fni_->Leave();
+  } while (Check(Token::COMMA));
+
+  ExpectSemicolon(CHECK_OK);
+  return block;
+}
+
+
 // If the variable declaration declares exactly one non-const
 // variable, then *var is set to that variable. In all other cases,
 // *var is untouched; in particular, it is the caller's responsibility
@@ -1670,6 +1785,15 @@ Block* Parser::ParseVariableDeclarations(
     Consume(Token::VAR);
   } else if (peek() == Token::CONST) {
     Consume(Token::CONST);
+    if (harmony_scoping_) {
+      ASSERT(var_context == kForStatement ||
+             var_context == kStatement);
+      // In harmony mode 'const' declarations are only allowed in source
+      // element positions and that is handled by ParseHarmonyConstDeclaration.
+      ReportMessage("unprotected_const", Vector<const char*>::empty());
+      *ok = false;
+      return NULL;
+    }
     if (top_scope_->is_strict_mode()) {
       ReportMessage("strict_const", Vector<const char*>::empty());
       *ok = false;
@@ -1683,6 +1807,7 @@ Block* Parser::ParseVariableDeclarations(
     Consume(Token::LET);
     if (var_context != kSourceElement &&
         var_context != kForStatement) {
+      // Let declarations are only allowed in source element positions.
       ASSERT(var_context == kStatement);
       ReportMessage("unprotected_let", Vector<const char*>::empty());
       *ok = false;
@@ -1740,8 +1865,10 @@ Block* Parser::ParseVariableDeclarations(
     // If we have a const declaration, in an inner scope, the proxy is always
     // bound to the declared variable (independent of possibly surrounding with
     // statements).
-    Declare(name, mode, NULL, is_const /* always bound for CONST! */,
-            CHECK_OK);
+    // For let/const declarations in harmony mode, we can also immediately
+    // pre-resolve the proxy because it resides in the same scope as the
+    // declaration.
+    Declare(name, mode, NULL, mode != VAR, CHECK_OK);
     nvars++;
     if (declaration_scope->num_var_or_const() > kMaxNumFunctionLocals) {
       ReportMessageAt(scanner().location(), "too_many_variables",
@@ -1883,9 +2010,9 @@ Block* Parser::ParseVariableDeclarations(
     // dynamically looked-up variables and constants (the start context
     // for constant lookups is always the function context, while it is
     // the top context for var declared variables). Sigh...
-    // For 'let' declared variables the initialization is in the same scope
-    // as the declaration. Thus dynamic lookups are unnecessary even if the
-    // block scope is inside a with.
+    // For 'let' and 'const' declared variables in harmony mode the
+    // initialization is in the same scope as the declaration. Thus dynamic
+    // lookups are unnecessary even if the block scope is inside a with.
     if (value != NULL) {
       VariableProxy* proxy = initialization_scope->NewUnresolved(name);
       Assignment* assignment =
@@ -3877,12 +4004,21 @@ FunctionLiteral* Parser::ParseFunctionLiteral(Handle<String> function_name,
     // future we can change the AST to only refer to VariableProxies
     // instead of Variables and Proxis as is the case now.
     if (type == FunctionLiteral::NAMED_EXPRESSION) {
-      Variable* fvar = top_scope_->DeclareFunctionVar(function_name);
+      VariableMode fvar_mode;
+      Token::Value fvar_init_op;
+      if (harmony_scoping_) {
+        fvar_mode = CONST_HARMONY;
+        fvar_init_op = Token::INIT_CONST_HARMONY;
+      } else {
+        fvar_mode = CONST;
+        fvar_init_op = Token::INIT_CONST;
+      }
+      Variable* fvar = top_scope_->DeclareFunctionVar(function_name, fvar_mode);
       VariableProxy* fproxy = top_scope_->NewUnresolved(function_name);
       fproxy->BindTo(fvar);
       body->Add(new(zone()) ExpressionStatement(
           new(zone()) Assignment(isolate(),
-                                 Token::INIT_CONST,
+                                 fvar_init_op,
                                  fproxy,
                                  new(zone()) ThisFunction(isolate()),
                                  RelocInfo::kNoPosition)));