Calling a generator function returns a generator object

src/parser.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 468 matching lines @@
   ~BlockState() { parser_->top_scope_ = outer_scope_; }
 
  private:
   Parser* parser_;
   Scope* outer_scope_;
 };
 
 
 Parser::FunctionState::FunctionState(Parser* parser,
                                      Scope* scope,
-                                     bool is_generator,
                                      Isolate* isolate)
     : next_materialized_literal_index_(JSFunction::kLiteralsPrefixSize),
       next_handler_index_(0),
       expected_property_count_(0),
-      is_generator_(is_generator),
       only_simple_this_property_assignments_(false),
       this_property_assignments_(isolate->factory()->empty_fixed_array()),
       parser_(parser),
       outer_function_state_(parser->current_function_state_),
       outer_scope_(parser->top_scope_),
+      generator_object_variable_(NULL),
       saved_ast_node_id_(isolate->ast_node_id()),
       factory_(isolate, parser->zone()) {
   parser->top_scope_ = scope;
   parser->current_function_state_ = this;
   isolate->set_ast_node_id(BailoutId::FirstUsable().ToInt());
 }
 
 
 Parser::FunctionState::~FunctionState() {
   parser_->top_scope_ = outer_scope_;
@@ skipping 125 matching lines @@
 
     // Compute the parsing mode.
     Mode mode = (FLAG_lazy && allow_lazy()) ? PARSE_LAZILY : PARSE_EAGERLY;
     if (allow_natives_syntax() ||
         extension_ != NULL ||
         scope->is_eval_scope()) {
       mode = PARSE_EAGERLY;
     }
     ParsingModeScope parsing_mode(this, mode);
 
-    bool is_generator = false;
     // Enters 'scope'.
-    FunctionState function_state(this, scope, is_generator, isolate());
+    FunctionState function_state(this, scope, isolate());
 
     top_scope_->SetLanguageMode(info->language_mode());
     ZoneList<Statement*>* body = new(zone()) ZoneList<Statement*>(16, zone());
     bool ok = true;
     int beg_loc = scanner().location().beg_pos;
     ParseSourceElements(body, Token::EOS, info->is_eval(), true, &ok);
     if (ok && !top_scope_->is_classic_mode()) {
       CheckOctalLiteral(beg_loc, scanner().location().end_pos, &ok);
     }
 
@@ skipping 93 matching lines @@
   FunctionLiteral* result = NULL;
 
   {
     // Parse the function literal.
     Scope* scope = NewScope(top_scope_, GLOBAL_SCOPE);
     info()->SetGlobalScope(scope);
     if (!info()->closure().is_null()) {
       scope = Scope::DeserializeScopeChain(info()->closure()->context(), scope,
                                            zone());
     }
-    bool is_generator = false;  // Top scope is not a generator.
-    FunctionState function_state(this, scope, is_generator, isolate());
+    FunctionState function_state(this, scope, isolate());
     ASSERT(scope->language_mode() != STRICT_MODE || !info()->is_classic_mode());
     ASSERT(scope->language_mode() != EXTENDED_MODE ||
            info()->is_extended_mode());
     ASSERT(info()->language_mode() == shared_info->language_mode());
     scope->SetLanguageMode(shared_info->language_mode());
     FunctionLiteral::Type type = shared_info->is_expression()
         ? (shared_info->is_anonymous()
               ? FunctionLiteral::ANONYMOUS_EXPRESSION
               : FunctionLiteral::NAMED_EXPRESSION)
         : FunctionLiteral::DECLARATION;
@@ skipping 253 matching lines @@
 
 
 void* Parser::ParseSourceElements(ZoneList<Statement*>* processor,
                                   int end_token,
                                   bool is_eval,
                                   bool is_global,
                                   bool* ok) {
   // SourceElements ::
   //   (ModuleElement)* <end_token>
 
+  // For generators, allocate and yield an iterator on function entry.

[Michael Starzinger, 2013/04/11 19:17:39]

Can we move this down into "ParseFunctionLiteral" right before this method is
called? I think it conceptually belongs to the function literal and not to it's
source elements. Also programs/scripts cannot be generators themselves.

[wingo, 2013/04/12 10:50:17]

Done.

+  if (is_generator()) {
+    ZoneList<Expression*>* arguments =
+        new(zone()) ZoneList<Expression*>(1, zone());
+    arguments->Add(factory()->NewThisFunction(), zone());
+    CallRuntime* allocation = factory()->NewCallRuntime(
+        isolate()->factory()->empty_string(),
+        Runtime::FunctionForId(Runtime::kCreateJSGeneratorObject),
+        arguments);
+    VariableProxy* init_proxy = factory()->NewVariableProxy(
+        current_function_state_->generator_object_variable());
+    Assignment* assignment = factory()->NewAssignment(
+        Token::INIT_VAR, init_proxy, allocation, RelocInfo::kNoPosition);
+    VariableProxy* get_proxy = factory()->NewVariableProxy(
+        current_function_state_->generator_object_variable());
+    Yield* yield = factory()->NewYield(
+        get_proxy, assignment, false, RelocInfo::kNoPosition);
+    processor->Add(factory()->NewExpressionStatement(yield), zone());
+  }
+
   // Allocate a target stack to use for this set of source
   // elements. This way, all scripts and functions get their own
   // target stack thus avoiding illegal breaks and continues across
   // functions.
   TargetScope scope(&this->target_stack_);
 
   ASSERT(processor != NULL);
   ThisNamedPropertyAssignmentFinder this_property_assignment_finder(isolate(),
                                                                     zone());
   bool directive_prologue = true;     // Parsing directive prologue.
@@ skipping 2050 matching lines @@
   return factory()->NewAssignment(op, expression, right, pos);
 }
 
 
 Expression* Parser::ParseYieldExpression(bool* ok) {
   // YieldExpression ::
   //   'yield' '*'? AssignmentExpression
   int position = scanner().peek_location().beg_pos;
   Expect(Token::YIELD, CHECK_OK);
   bool is_yield_star = Check(Token::MUL);
+  Expression* generator_object = factory()->NewVariableProxy(
+      current_function_state_->generator_object_variable());
   Expression* expression = ParseAssignmentExpression(false, CHECK_OK);
-  return factory()->NewYield(expression, is_yield_star, position);
+  return factory()->NewYield(generator_object, expression, is_yield_star,
+                             position);
 }
 
 
 // Precedence = 3
 Expression* Parser::ParseConditionalExpression(bool accept_IN, bool* ok) {
   // ConditionalExpression ::
   //   LogicalOrExpression
   //   LogicalOrExpression '?' AssignmentExpression ':' AssignmentExpression
 
   // We start using the binary expression parser for prec >= 4 only!
@@ skipping 1264 matching lines @@
   FunctionLiteral::ParameterFlag duplicate_parameters =
       FunctionLiteral::kNoDuplicateParameters;
   FunctionLiteral::IsParenthesizedFlag parenthesized = parenthesized_function_
       ? FunctionLiteral::kIsParenthesized
       : FunctionLiteral::kNotParenthesized;
   FunctionLiteral::IsGeneratorFlag generator = is_generator
       ? FunctionLiteral::kIsGenerator
       : FunctionLiteral::kNotGenerator;
   AstProperties ast_properties;
   // Parse function body.
-  { FunctionState function_state(this, scope, is_generator, isolate());
+  { FunctionState function_state(this, scope, isolate());
     top_scope_->SetScopeName(function_name);
-    // For generators, allocating variables in contexts is currently a win
-    // because it minimizes the work needed to suspend and resume an activation.
-    if (is_generator) top_scope_->ForceContextAllocation();
+
+    if (is_generator) {
+      // For generators, allocating variables in contexts is currently a win
+      // because it minimizes the work needed to suspend and resume an
+      // activation.
+      top_scope_->ForceContextAllocation();
+
+      // Calling a generator returns a generator object.  That object is stored
+      // in a temporary variable, a definition that is used by "yield"
+      // expressions.  Presence of a variable for the generator object in the
+      // FunctionState indicates that this function is a generator.
+      Handle<String> tempname = isolate()->factory()->InternalizeOneByteString(
+          STATIC_ASCII_VECTOR(".generator_object"));
+      Variable* temp = top_scope_->DeclarationScope()->NewTemporary(tempname);
+      function_state.set_generator_object_variable(temp);
+    }
 
     //  FormalParameterList ::
     //    '(' (Identifier)*[','] ')'
     Expect(Token::LPAREN, CHECK_OK);
     scope->set_start_position(scanner().location().beg_pos);
     Scanner::Location name_loc = Scanner::Location::invalid();
     Scanner::Location dupe_loc = Scanner::Location::invalid();
     Scanner::Location reserved_loc = Scanner::Location::invalid();
 
     bool done = (peek() == Token::RPAREN);
@@ skipping 1567 matching lines @@
       ASSERT(info()->isolate()->has_pending_exception());
     } else {
       result = ParseProgram();
     }
   }
   info()->SetFunction(result);
   return (result != NULL);
 }
 
 } }  // namespace v8::internal