[esnext] implement frontend changes for async/await proposal

BUG=v8:4483
LOG=Y
R=littledan@chromium.org, adamk@chromium.org

Review-Url: https://codereview.chromium.org/1841543003
Cr-Commit-Position: refs/heads/master@{#36261}

src/ast/ast-value-factory.h

@@ -242,6 +242,8 @@ class AstValue : public ZoneObject {
 #define STRING_CONSTANTS(F)                     \
   F(anonymous_function, "(anonymous function)") \
   F(arguments, "arguments")                     \
+  F(async, "async")                             \
+  F(await, "await")                             \
   F(constructor, "constructor")                 \
   F(default, "default")                         \
   F(done, "done")                               \

src/ast/ast.h

@@ -2587,12 +2587,12 @@ class FunctionLiteral final : public Expression {
   int start_position() const;
   int end_position() const;
   int SourceSize() const { return end_position() - start_position(); }
-  bool is_declaration() const { return IsDeclaration::decode(bitfield_); }
+  bool is_declaration() const { return function_type() == kDeclaration; }
   bool is_named_expression() const {
-    return IsNamedExpression::decode(bitfield_);
+    return function_type() == kNamedExpression;
   }
   bool is_anonymous_expression() const {
-    return IsAnonymousExpression::decode(bitfield_);
+    return function_type() == kAnonymousExpression;
   }
   LanguageMode language_mode() const;
 
@@ -2669,6 +2669,9 @@ class FunctionLiteral final : public Expression {
     bitfield_ = ShouldBeUsedOnceHint::update(bitfield_, true);
   }
 
+  FunctionType function_type() const {
+    return FunctionTypeBits::decode(bitfield_);
+  }
   FunctionKind kind() const { return FunctionKindBits::decode(bitfield_); }
 
   int ast_node_count() { return ast_properties_.node_count(); }
@@ -2714,10 +2717,7 @@ class FunctionLiteral final : public Expression {
         function_token_position_(RelocInfo::kNoPosition),
         yield_count_(0) {
     bitfield_ =
-        IsDeclaration::encode(function_type == kDeclaration) |
-        IsNamedExpression::encode(function_type == kNamedExpression) |
-        IsAnonymousExpression::encode(function_type == kAnonymousExpression) |
-        Pretenure::encode(false) |
+        FunctionTypeBits::encode(function_type) | Pretenure::encode(false) |
         HasDuplicateParameters::encode(has_duplicate_parameters ==
                                        kHasDuplicateParameters) |
         IsFunction::encode(is_function) |
@@ -2727,15 +2727,13 @@ class FunctionLiteral final : public Expression {
   }
 
  private:
-  class IsDeclaration : public BitField16<bool, 0, 1> {};
-  class IsNamedExpression : public BitField16<bool, 1, 1> {};
-  class IsAnonymousExpression : public BitField16<bool, 2, 1> {};
-  class Pretenure : public BitField16<bool, 3, 1> {};
-  class HasDuplicateParameters : public BitField16<bool, 4, 1> {};
-  class IsFunction : public BitField16<bool, 5, 1> {};
-  class ShouldEagerCompile : public BitField16<bool, 6, 1> {};
-  class ShouldBeUsedOnceHint : public BitField16<bool, 7, 1> {};
-  class FunctionKindBits : public BitField16<FunctionKind, 8, 8> {};
+  class FunctionTypeBits : public BitField16<FunctionType, 0, 2> {};
+  class Pretenure : public BitField16<bool, 2, 1> {};
+  class HasDuplicateParameters : public BitField16<bool, 3, 1> {};
+  class IsFunction : public BitField16<bool, 4, 1> {};
+  class ShouldEagerCompile : public BitField16<bool, 5, 1> {};
+  class ShouldBeUsedOnceHint : public BitField16<bool, 6, 1> {};
+  class FunctionKindBits : public BitField16<FunctionKind, 7, 9> {};
 
   // Start with 16-bit field, which should get packed together
   // with Expression's trailing 16-bit field.

src/bootstrapper.cc

@@ -2457,6 +2457,7 @@ EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_string_padding)
 #ifdef V8_I18N_SUPPORT
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(icu_case_mapping)
 #endif
+EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_async_await)
 
 void InstallPublicSymbol(Factory* factory, Handle<Context> native_context,
                          const char* name, Handle<Symbol> value) {
@@ -3030,6 +3031,7 @@ bool Genesis::InstallExperimentalNatives() {
   static const char* icu_case_mapping_natives[] = {"native icu-case-mapping.js",
                                                    nullptr};
 #endif
+  static const char* harmony_async_await_natives[] = {nullptr};
 
   for (int i = ExperimentalNatives::GetDebuggerCount();
        i < ExperimentalNatives::GetBuiltinsCount(); i++) {

src/flag-definitions.h

@@ -204,14 +204,16 @@ DEFINE_IMPLICATION(es_staging, move_object_start)
   V(harmony_simd, "harmony simd")                                       \
   V(harmony_do_expressions, "harmony do-expressions")                   \
   V(harmony_regexp_property, "harmony unicode regexp property classes") \
-  V(icu_case_mapping, "case mapping with ICU rather than Unibrow")
+  V(icu_case_mapping, "case mapping with ICU rather than Unibrow")      \
+  V(harmony_async_await, "harmony async-await")
 #else
-#define HARMONY_INPROGRESS(V)                                  \
-  V(harmony_function_sent, "harmony function.sent")            \
-  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")    \
-  V(harmony_simd, "harmony simd")                              \
-  V(harmony_do_expressions, "harmony do-expressions")          \
-  V(harmony_regexp_property, "harmony unicode regexp property classes")
+#define HARMONY_INPROGRESS(V)                                           \
+  V(harmony_function_sent, "harmony function.sent")                     \
+  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")             \
+  V(harmony_simd, "harmony simd")                                       \
+  V(harmony_do_expressions, "harmony do-expressions")                   \
+  V(harmony_regexp_property, "harmony unicode regexp property classes") \
+  V(harmony_async_await, "harmony async-await")
 #endif
 
 // Features that are complete (but still behind --harmony/es-staging flag).

src/globals.h

@@ -963,11 +963,14 @@ enum FunctionKind {
   kBaseConstructor = 1 << 5,
   kGetterFunction = 1 << 6,
   kSetterFunction = 1 << 7,
+  kAsyncFunction = 1 << 8,
   kAccessorFunction = kGetterFunction | kSetterFunction,
   kDefaultBaseConstructor = kDefaultConstructor | kBaseConstructor,
   kDefaultSubclassConstructor = kDefaultConstructor | kSubclassConstructor,
   kClassConstructor =
       kBaseConstructor | kSubclassConstructor | kDefaultConstructor,
+  kAsyncArrowFunction = kArrowFunction | kAsyncFunction,
+  kAsyncConciseMethod = kAsyncFunction | kConciseMethod
 };
 
 inline bool IsValidFunctionKind(FunctionKind kind) {
@@ -982,7 +985,10 @@ inline bool IsValidFunctionKind(FunctionKind kind) {
          kind == FunctionKind::kDefaultBaseConstructor ||
          kind == FunctionKind::kDefaultSubclassConstructor ||
          kind == FunctionKind::kBaseConstructor ||
-         kind == FunctionKind::kSubclassConstructor;
+         kind == FunctionKind::kSubclassConstructor ||
+         kind == FunctionKind::kAsyncFunction ||
+         kind == FunctionKind::kAsyncArrowFunction ||
+         kind == FunctionKind::kAsyncConciseMethod;
 }
 
 
@@ -997,6 +1003,10 @@ inline bool IsGeneratorFunction(FunctionKind kind) {
   return kind & FunctionKind::kGeneratorFunction;
 }
 
+inline bool IsAsyncFunction(FunctionKind kind) {
+  DCHECK(IsValidFunctionKind(kind));
+  return kind & FunctionKind::kAsyncFunction;
+}
 
 inline bool IsConciseMethod(FunctionKind kind) {
   DCHECK(IsValidFunctionKind(kind));

src/messages.h

@@ -358,6 +358,7 @@ class CallSite {
   T(BadSetterArity, "Setter must have exactly one formal parameter.")          \
   T(ConstructorIsAccessor, "Class constructor may not be an accessor")         \
   T(ConstructorIsGenerator, "Class constructor may not be a generator")        \
+  T(ConstructorIsAsync, "Class constructor may not be an async method")        \
   T(DerivedConstructorReturn,                                                  \
     "Derived constructors may only return object or undefined")                \
   T(DuplicateConstructor, "A class may only have one constructor")             \
@@ -432,6 +433,10 @@ class CallSite {
   T(TemplateOctalLiteral,                                                      \
     "Octal literals are not allowed in template strings.")                     \
   T(ThisFormalParameter, "'this' is not a valid formal parameter name")        \
+  T(AwaitBindingIdentifier,                                                    \
+    "'await' is not a valid identifier name in an async function")             \
+  T(AwaitExpressionFormalParameter,                                            \
+    "Illegal await-expression in formal parameters of async function")         \
   T(TooManyArguments,                                                          \
     "Too many arguments in function call (only 65535 allowed)")                \
   T(TooManyParameters,                                                         \

src/objects-inl.h

@@ -5786,6 +5786,7 @@ BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, dont_crankshaft,
 BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, dont_flush, kDontFlush)
 BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, is_arrow, kIsArrow)
 BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, is_generator, kIsGenerator)
+BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, is_async, kIsAsyncFunction)
 BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, is_concise_method,
                kIsConciseMethod)
 BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, is_getter_function,
@@ -5795,6 +5796,10 @@ BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, is_setter_function,
 BOOL_ACCESSORS(SharedFunctionInfo, compiler_hints, is_default_constructor,
                kIsDefaultConstructor)
 
+inline bool SharedFunctionInfo::is_resumable() const {
+  return is_generator() || is_async();
+}
+
 bool Script::HasValidSource() {
   Object* src = this->source();
   if (!src->IsString()) return true;

src/objects.h

@@ -4295,7 +4295,7 @@ class ScopeInfo : public FixedArray {
   class HasSimpleParametersField
       : public BitField<bool, AsmFunctionField::kNext, 1> {};
   class FunctionKindField
-      : public BitField<FunctionKind, HasSimpleParametersField::kNext, 8> {};
+      : public BitField<FunctionKind, HasSimpleParametersField::kNext, 9> {};
 
   // BitFields representing the encoded information for context locals in the
   // ContextLocalInfoEntries part.
@@ -6853,6 +6853,13 @@ class SharedFunctionInfo: public HeapObject {
   // Indicates that this function is a generator.
   DECL_BOOLEAN_ACCESSORS(is_generator)
 
+  // Indicates that this function is an async function.
+  DECL_BOOLEAN_ACCESSORS(is_async)
+
+  // Indicates that this function can be suspended, either via YieldExpressions
+  // or AwaitExpressions.
+  inline bool is_resumable() const;
+
   // Indicates that this function is an arrow function.
   DECL_BOOLEAN_ACCESSORS(is_arrow)
 
@@ -7149,6 +7156,7 @@ class SharedFunctionInfo: public HeapObject {
     kIsGetterFunction,
     kIsSetterFunction,
     // byte 3
+    kIsAsyncFunction,
     kDeserialized,
     kIsDeclaration,
     kCompilerHintsCount,  // Pseudo entry
@@ -7171,7 +7179,7 @@ class SharedFunctionInfo: public HeapObject {
   ASSERT_FUNCTION_KIND_ORDER(kSetterFunction, kIsSetterFunction);
 #undef ASSERT_FUNCTION_KIND_ORDER
 
-  class FunctionKindBits : public BitField<FunctionKind, kIsArrow, 8> {};
+  class FunctionKindBits : public BitField<FunctionKind, kIsArrow, 9> {};
 
   class DeoptCountBits : public BitField<int, 0, 4> {};
   class OptReenableTriesBits : public BitField<int, 4, 18> {};

src/parsing/expression-classifier.h

@@ -40,18 +40,22 @@ class ExpressionClassifier {
     LetPatternProduction = 1 << 7,
     CoverInitializedNameProduction = 1 << 8,
     TailCallExpressionProduction = 1 << 9,
+    AsyncArrowFormalParametersProduction = 1 << 10,
+    AsyncBindingPatternProduction = 1 << 11,
 
     ExpressionProductions =
         (ExpressionProduction | FormalParameterInitializerProduction |
          TailCallExpressionProduction),
-    PatternProductions = (BindingPatternProduction |
-                          AssignmentPatternProduction | LetPatternProduction),
+    PatternProductions =
+        (BindingPatternProduction | AssignmentPatternProduction |
+         LetPatternProduction | AsyncBindingPatternProduction),
     FormalParametersProductions = (DistinctFormalParametersProduction |
                                    StrictModeFormalParametersProduction),
     StandardProductions = ExpressionProductions | PatternProductions,
     AllProductions =
         (StandardProductions | FormalParametersProductions |
-         ArrowFormalParametersProduction | CoverInitializedNameProduction)
+         ArrowFormalParametersProduction | CoverInitializedNameProduction |
+         AsyncArrowFormalParametersProduction | AsyncBindingPatternProduction)
   };
 
   enum FunctionProperties { NonSimpleParameter = 1 << 0 };
@@ -112,6 +116,14 @@ class ExpressionClassifier {
 
   bool is_valid_let_pattern() const { return is_valid(LetPatternProduction); }
 
+  bool is_valid_async_arrow_formal_parameters() const {
+    return is_valid(AsyncArrowFormalParametersProduction);
+  }
+
+  bool is_valid_async_binding_pattern() const {
+    return is_valid(AsyncBindingPatternProduction);
+  }
+
   const Error& expression_error() const { return expression_error_; }
 
   const Error& formal_parameter_initializer_error() const {
@@ -151,6 +163,13 @@ class ExpressionClassifier {
   const Error& tail_call_expression_error() const {
     return tail_call_expression_error_;
   }
+  const Error& async_arrow_formal_parameters_error() const {
+    return async_arrow_formal_parameters_error_;
+  }
+
+  const Error& async_binding_pattern_error() const {
+    return async_binding_pattern_error_;
+  }
 
   bool is_simple_parameter_list() const {
     return !(function_properties_ & NonSimpleParameter);
@@ -228,6 +247,26 @@ class ExpressionClassifier {
     arrow_formal_parameters_error_.arg = arg;
   }
 
+  void RecordAsyncArrowFormalParametersError(const Scanner::Location& loc,
+                                             MessageTemplate::Template message,
+                                             const char* arg = nullptr) {
+    if (!is_valid_async_arrow_formal_parameters()) return;
+    invalid_productions_ |= AsyncArrowFormalParametersProduction;
+    async_arrow_formal_parameters_error_.location = loc;
+    async_arrow_formal_parameters_error_.message = message;
+    async_arrow_formal_parameters_error_.arg = arg;
+  }
+
+  void RecordAsyncBindingPatternError(const Scanner::Location& loc,
+                                      MessageTemplate::Template message,
+                                      const char* arg = nullptr) {
+    if (!is_valid_async_binding_pattern()) return;
+    invalid_productions_ |= AsyncBindingPatternProduction;
+    async_binding_pattern_error_.location = loc;
+    async_binding_pattern_error_.message = message;
+    async_binding_pattern_error_.arg = arg;
+  }
+
   void RecordDuplicateFormalParameterError(const Scanner::Location& loc) {
     if (!is_valid_formal_parameter_list_without_duplicates()) return;
     invalid_productions_ |= DistinctFormalParametersProduction;
@@ -326,6 +365,11 @@ class ExpressionClassifier {
         cover_initialized_name_error_ = inner->cover_initialized_name_error_;
       if (errors & TailCallExpressionProduction)
         tail_call_expression_error_ = inner->tail_call_expression_error_;
+      if (errors & AsyncArrowFormalParametersProduction)
+        async_arrow_formal_parameters_error_ =
+            inner->async_arrow_formal_parameters_error_;
+      if (errors & AsyncBindingPatternProduction)
+        async_binding_pattern_error_ = inner->async_binding_pattern_error_;
     }
 
     // As an exception to the above, the result continues to be a valid arrow
@@ -373,6 +417,8 @@ class ExpressionClassifier {
   Error let_pattern_error_;
   Error cover_initialized_name_error_;
   Error tail_call_expression_error_;
+  Error async_arrow_formal_parameters_error_;
+  Error async_binding_pattern_error_;
   DuplicateFinder* duplicate_finder_;
 };
 

src/parsing/parser.h

@@ -355,6 +355,7 @@ class ParserTraits {
   bool IsArguments(const AstRawString* identifier) const;
   bool IsEvalOrArguments(const AstRawString* identifier) const;
   bool IsUndefined(const AstRawString* identifier) const;
+  bool IsAwait(const AstRawString* identifier) const;
   V8_INLINE bool IsFutureStrictReserved(const AstRawString* identifier) const;
 
   // Returns true if the expression is of type "this.foo".
@@ -554,6 +555,8 @@ class ParserTraits {
       const Scanner::Location& params_loc,
       Scanner::Location* duplicate_loc, bool* ok);
 
+  V8_INLINE Expression* ParseAsyncFunctionExpression(bool* ok);
+
   V8_INLINE DoExpression* ParseDoExpression(bool* ok);
 
   void ReindexLiterals(const ParserFormalParameters& parameters);
@@ -637,6 +640,8 @@ class ParserTraits {
                                       ZoneList<v8::internal::Expression*>* args,
                                       int pos);
 
+  Expression* ExpressionListToExpression(ZoneList<Expression*>* args);
+
   // Rewrite all DestructuringAssignments in the current FunctionState.
   V8_INLINE void RewriteDestructuringAssignments();
 
@@ -645,6 +650,8 @@ class ParserTraits {
   V8_INLINE Expression* RewriteAssignExponentiation(Expression* left,
                                                     Expression* right, int pos);
 
+  V8_INLINE Expression* RewriteAwaitExpression(Expression* value, int pos);
+
   V8_INLINE void QueueDestructuringAssignmentForRewriting(
       Expression* assignment);
   V8_INLINE void QueueNonPatternForRewriting(Expression* expr);
@@ -772,7 +779,13 @@ class Parser : public ParserBase<ParserTraits> {
   Statement* ParseFunctionDeclaration(bool* ok);
   Statement* ParseHoistableDeclaration(ZoneList<const AstRawString*>* names,
                                       bool* ok);
-  Statement* ParseHoistableDeclaration(int pos, bool is_generator,
+  Statement* ParseHoistableDeclaration(int pos, ParseFunctionFlags flags,
+                                       ZoneList<const AstRawString*>* names,
+                                       bool* ok);
+  Statement* ParseAsyncFunctionDeclaration(ZoneList<const AstRawString*>* names,
+                                           bool* ok);
+  Expression* ParseAsyncFunctionExpression(bool* ok);
+  Statement* ParseFunctionDeclaration(int pos, bool is_generator,
                                       ZoneList<const AstRawString*>* names,
                                       bool* ok);
   Statement* ParseClassDeclaration(ZoneList<const AstRawString*>* names,
@@ -1255,6 +1268,9 @@ void ParserTraits::AddParameterInitializationBlock(
   }
 }
 
+Expression* ParserTraits::ParseAsyncFunctionExpression(bool* ok) {
+  return parser_->ParseAsyncFunctionExpression(ok);
+}
 
 DoExpression* ParserTraits::ParseDoExpression(bool* ok) {
   return parser_->ParseDoExpression(ok);

src/parsing/preparser.cc

@@ -51,6 +51,8 @@ PreParserIdentifier PreParserTraits::GetSymbol(Scanner* scanner) {
     return PreParserIdentifier::Static();
   } else if (scanner->current_token() == Token::YIELD) {
     return PreParserIdentifier::Yield();
+  } else if (scanner->current_token() == Token::ASYNC) {
+    return PreParserIdentifier::Async();
   }
   if (scanner->UnescapedLiteralMatches("eval", 4)) {
     return PreParserIdentifier::Eval();
@@ -193,6 +195,13 @@ PreParser::Statement PreParser::ParseStatementListItem(bool* ok) {
         return ParseVariableStatement(kStatementListItem, ok);
       }
       break;
+    case Token::ASYNC:
+      if (allow_harmony_async_await() && PeekAhead() == Token::FUNCTION &&
+          !scanner()->HasAnyLineTerminatorAfterNext()) {
+        Consume(Token::ASYNC);
+        return ParseAsyncFunctionDeclaration(ok);
+      }
+    /* falls through */
     default:
       break;
   }
@@ -381,22 +390,44 @@ PreParser::Statement PreParser::ParseSubStatement(
   }
 }
 
-
 PreParser::Statement PreParser::ParseHoistableDeclaration(
-    int pos, bool is_generator, bool* ok) {
+    int pos, ParseFunctionFlags flags, bool* ok) {
+  const bool is_generator = flags & ParseFunctionFlags::kIsGenerator;
+  const bool is_async = flags & ParseFunctionFlags::kIsAsync;
+  DCHECK(!is_generator || !is_async);
+
   bool is_strict_reserved = false;
   Identifier name = ParseIdentifierOrStrictReservedWord(
       &is_strict_reserved, CHECK_OK);
+
+  if (V8_UNLIKELY(is_async_function() && this->IsAwait(name))) {
+    ReportMessageAt(scanner()->location(),
+                    MessageTemplate::kAwaitBindingIdentifier);
+    *ok = false;
+    return Statement::Default();
+  }
+
   ParseFunctionLiteral(name, scanner()->location(),
                        is_strict_reserved ? kFunctionNameIsStrictReserved
                                           : kFunctionNameValidityUnknown,
                        is_generator ? FunctionKind::kGeneratorFunction
-                                    : FunctionKind::kNormalFunction,
+                                    : is_async ? FunctionKind::kAsyncFunction
+                                               : FunctionKind::kNormalFunction,
                        pos, FunctionLiteral::kDeclaration, language_mode(),
                        CHECK_OK);
   return Statement::FunctionDeclaration();
 }
 
+PreParser::Statement PreParser::ParseAsyncFunctionDeclaration(bool* ok) {
+  // AsyncFunctionDeclaration ::
+  //   async [no LineTerminator here] function BindingIdentifier[Await]
+  //       ( FormalParameters[Await] ) { AsyncFunctionBody }
+  DCHECK_EQ(scanner()->current_token(), Token::ASYNC);
+  int pos = position();
+  Expect(Token::FUNCTION, CHECK_OK);
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsAsync;
+  return ParseHoistableDeclaration(pos, flags, ok);
+}
 
 PreParser::Statement PreParser::ParseHoistableDeclaration(bool* ok) {
   // FunctionDeclaration ::
@@ -404,10 +435,14 @@ PreParser::Statement PreParser::ParseHoistableDeclaration(bool* ok) {
   // GeneratorDeclaration ::
   //   'function' '*' Identifier '(' FormalParameterListopt ')'
   //      '{' FunctionBody '}'
+
   Expect(Token::FUNCTION, CHECK_OK);
   int pos = position();
-  bool is_generator = Check(Token::MUL);
-  return ParseHoistableDeclaration(pos, is_generator, CHECK_OK);
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsNormal;
+  if (Check(Token::MUL)) {
+    flags |= ParseFunctionFlags::kIsGenerator;
+  }
+  return ParseHoistableDeclaration(pos, flags, ok);
 }
 
 
@@ -566,15 +601,17 @@ PreParser::Statement PreParser::ParseVariableDeclarations(
 PreParser::Statement PreParser::ParseFunctionDeclaration(bool* ok) {
   Consume(Token::FUNCTION);
   int pos = position();
-  bool is_generator = Check(Token::MUL);
-  if (allow_harmony_restrictive_declarations() && is_generator) {
-    PreParserTraits::ReportMessageAt(
-        scanner()->location(),
-        MessageTemplate::kGeneratorInLegacyContext);
-    *ok = false;
-    return Statement::Default();
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsNormal;
+  if (Check(Token::MUL)) {
+    flags |= ParseFunctionFlags::kIsGenerator;
+    if (allow_harmony_restrictive_declarations()) {
+      PreParserTraits::ReportMessageAt(
+          scanner()->location(), MessageTemplate::kGeneratorInLegacyContext);
+      *ok = false;
+      return Statement::Default();
+    }
   }
-  return ParseHoistableDeclaration(pos, is_generator, ok);
+  return ParseHoistableDeclaration(pos, flags, ok);
 }
 
 PreParser::Statement PreParser::ParseExpressionOrLabelledStatement(
@@ -1111,6 +1148,37 @@ PreParser::Expression PreParser::ParseFunctionLiteral(
   return Expression::Default();
 }
 
+PreParser::Expression PreParser::ParseAsyncFunctionExpression(bool* ok) {
+  // AsyncFunctionDeclaration ::
+  //   async [no LineTerminator here] function ( FormalParameters[Await] )
+  //       { AsyncFunctionBody }
+  //
+  //   async [no LineTerminator here] function BindingIdentifier[Await]
+  //       ( FormalParameters[Await] ) { AsyncFunctionBody }
+  int pos = position();
+  Expect(Token::FUNCTION, CHECK_OK);
+  bool is_strict_reserved = false;
+  Identifier name;
+  FunctionLiteral::FunctionType type = FunctionLiteral::kAnonymousExpression;
+
+  if (peek_any_identifier()) {
+    type = FunctionLiteral::kNamedExpression;
+    name = ParseIdentifierOrStrictReservedWord(&is_strict_reserved, CHECK_OK);
+    if (this->IsAwait(name)) {
+      ReportMessageAt(scanner()->location(),
+                      MessageTemplate::kAwaitBindingIdentifier);
+      *ok = false;
+      return Expression::Default();
+    }
+  }
+
+  ParseFunctionLiteral(name, scanner()->location(),
+                       is_strict_reserved ? kFunctionNameIsStrictReserved
+                                          : kFunctionNameValidityUnknown,
+                       FunctionKind::kAsyncFunction, pos, type, language_mode(),
+                       CHECK_OK);
+  return Expression::Default();
+}
 
 void PreParser::ParseLazyFunctionLiteralBody(bool* ok,
                                              Scanner::BookmarkScope* bookmark) {
@@ -1172,12 +1240,11 @@ PreParserExpression PreParser::ParseClassLiteral(
   while (peek() != Token::RBRACE) {
     if (Check(Token::SEMICOLON)) continue;
     const bool in_class = true;
-    const bool is_static = false;
     bool is_computed_name = false;  // Classes do not care about computed
                                     // property names here.
     Identifier name;
     ExpressionClassifier property_classifier(this);
-    ParsePropertyDefinition(&checker, in_class, has_extends, is_static,
+    ParsePropertyDefinition(&checker, in_class, has_extends, MethodKind::Normal,
                             &is_computed_name, &has_seen_constructor,
                             &property_classifier, &name, CHECK_OK);
     ValidateExpression(&property_classifier, CHECK_OK);

src/parsing/preparser.h

@@ -61,6 +61,9 @@ class PreParserIdentifier {
   static PreParserIdentifier Await() {
     return PreParserIdentifier(kAwaitIdentifier);
   }
+  static PreParserIdentifier Async() {
+    return PreParserIdentifier(kAsyncIdentifier);
+  }
   bool IsEval() const { return type_ == kEvalIdentifier; }
   bool IsArguments() const { return type_ == kArgumentsIdentifier; }
   bool IsEvalOrArguments() const { return IsEval() || IsArguments(); }
@@ -72,6 +75,7 @@ class PreParserIdentifier {
   bool IsConstructor() const { return type_ == kConstructorIdentifier; }
   bool IsEnum() const { return type_ == kEnumIdentifier; }
   bool IsAwait() const { return type_ == kAwaitIdentifier; }
+  bool IsAsync() const { return type_ == kAsyncIdentifier; }
   bool IsFutureStrictReserved() const {
     return type_ == kFutureStrictReservedIdentifier ||
            type_ == kLetIdentifier || type_ == kStaticIdentifier ||
@@ -100,7 +104,8 @@ class PreParserIdentifier {
     kPrototypeIdentifier,
     kConstructorIdentifier,
     kEnumIdentifier,
-    kAwaitIdentifier
+    kAwaitIdentifier,
+    kAsyncIdentifier
   };
 
   explicit PreParserIdentifier(Type type) : type_(type) {}
@@ -622,6 +627,14 @@ class PreParserTraits {
     return identifier.IsArguments();
   }
 
+  static bool IsAwait(PreParserIdentifier identifier) {
+    return identifier.IsAwait();
+  }
+
+  static bool IsAsync(PreParserIdentifier identifier) {
+    return identifier.IsAsync();
+  }
+
   static bool IsEvalOrArguments(PreParserIdentifier identifier) {
     return identifier.IsEvalOrArguments();
   }
@@ -865,6 +878,8 @@ class PreParserTraits {
       PreParserExpression expression, const Scanner::Location& params_loc,
       Scanner::Location* duplicate_loc, bool* ok);
 
+  V8_INLINE PreParserExpression ParseAsyncFunctionExpression(bool* ok);
+
   void ReindexLiterals(const PreParserFormalParameters& paramaters) {}
 
   struct TemplateLiteralState {};
@@ -937,6 +952,11 @@ class PreParserTraits {
                                            PreParserExpressionList args,
                                            int pos);
 
+  inline PreParserExpression ExpressionListToExpression(
+      PreParserExpressionList args) {
+    return PreParserExpression::Default();
+  }
+
   inline void RewriteDestructuringAssignments() {}
 
   inline PreParserExpression RewriteExponentiation(PreParserExpression left,
@@ -960,6 +980,9 @@ class PreParserTraits {
   inline void RewriteNonPattern(Type::ExpressionClassifier* classifier,
                                 bool* ok);
 
+  inline PreParserExpression RewriteAwaitExpression(PreParserExpression value,
+                                                    int pos);
+
   V8_INLINE Zone* zone() const;
   V8_INLINE ZoneList<PreParserExpression>* GetNonPatternList() const;
 
@@ -1076,8 +1099,11 @@ class PreParser : public ParserBase<PreParserTraits> {
                               bool* ok);
   Statement ParseScopedStatement(bool legacy, bool* ok);
   Statement ParseHoistableDeclaration(bool* ok);
-  Statement ParseHoistableDeclaration(int pos, bool is_generator, bool* ok);
+  Statement ParseHoistableDeclaration(int pos, ParseFunctionFlags flags,
+                                      bool* ok);
   Statement ParseFunctionDeclaration(bool* ok);
+  Statement ParseAsyncFunctionDeclaration(bool* ok);
+  Expression ParseAsyncFunctionExpression(bool* ok);
   Statement ParseClassDeclaration(bool* ok);
   Statement ParseBlock(bool* ok);
   Statement ParseVariableStatement(VariableDeclarationContext var_context,
@@ -1166,6 +1192,9 @@ void PreParserTraits::ParseArrowFunctionFormalParameterList(
   // lists that are too long.
 }
 
+PreParserExpression PreParserTraits::ParseAsyncFunctionExpression(bool* ok) {
+  return pre_parser_->ParseAsyncFunctionExpression(ok);
+}
 
 PreParserExpression PreParserTraits::ParseDoExpression(bool* ok) {
   return pre_parser_->ParseDoExpression(ok);
@@ -1177,6 +1206,10 @@ void PreParserTraits::RewriteNonPattern(Type::ExpressionClassifier* classifier,
   pre_parser_->ValidateExpression(classifier, ok);
 }
 
+PreParserExpression PreParserTraits::RewriteAwaitExpression(
+    PreParserExpression value, int pos) {
+  return value;
+}
 
 Zone* PreParserTraits::zone() const {
   return pre_parser_->function_state_->scope()->zone();

src/parsing/scanner.cc

@@ -249,6 +249,7 @@ Token::Value Scanner::Next() {
   if (V8_UNLIKELY(next_next_.token != Token::UNINITIALIZED)) {
     next_ = next_next_;
     next_next_.token = Token::UNINITIALIZED;
+    has_line_terminator_before_next_ = has_line_terminator_after_next_;
     return current_.token;
   }
   has_line_terminator_before_next_ = false;
@@ -274,7 +275,12 @@ Token::Value Scanner::PeekAhead() {
     return next_next_.token;
   }
   TokenDesc prev = current_;
+  bool has_line_terminator_before_next =
+      has_line_terminator_before_next_ || has_multiline_comment_before_next_;
   Next();
+  has_line_terminator_after_next_ =
+      has_line_terminator_before_next_ || has_multiline_comment_before_next_;
+  has_line_terminator_before_next_ = has_line_terminator_before_next;
   Token::Value ret = next_.token;
   next_next_ = next_;
   next_ = current_;
@@ -1136,6 +1142,7 @@ uc32 Scanner::ScanUnicodeEscape() {
 
 #define KEYWORDS(KEYWORD_GROUP, KEYWORD)                    \
   KEYWORD_GROUP('a')                                        \
+  KEYWORD("async", Token::ASYNC)                            \
   KEYWORD("await", Token::AWAIT)                            \
   KEYWORD_GROUP('b')                                        \
   KEYWORD("break", Token::BREAK)                            \

src/parsing/scanner.h

@@ -442,6 +442,12 @@ class Scanner {
            has_multiline_comment_before_next_;
   }
 
+  bool HasAnyLineTerminatorAfterNext() {
+    Token::Value ensure_next_next = PeekAhead();
+    USE(ensure_next_next);
+    return has_line_terminator_after_next_;
+  }
+
   // Scans the input as a regular expression pattern, previous
   // character(s) must be /(=). Returns true if a pattern is scanned.
   bool ScanRegExpPattern(bool seen_equal);
@@ -786,6 +792,7 @@ class Scanner {
   // Whether there is a multi-line comment that contains a
   // line-terminator after the current token, and before the next.
   bool has_multiline_comment_before_next_;
+  bool has_line_terminator_after_next_;
 
   // Whether this scanner encountered an HTML comment.
   bool found_html_comment_;

src/parsing/token.h

@@ -149,6 +149,7 @@ namespace internal {
                                                                      \
   /* Future reserved words (ECMA-262, section 7.6.1.2). */           \
   T(FUTURE_STRICT_RESERVED_WORD, NULL, 0)                            \
+  K(ASYNC, "async", 0)                                               \
   /* `await` is a reserved word in module code only */               \
   K(AWAIT, "await", 0)                                               \
   K(CLASS, "class", 0)                                               \
@@ -201,6 +202,7 @@ class Token {
                            bool is_generator, bool is_module) {
     switch (tok) {
       case IDENTIFIER:
+      case ASYNC:
         return true;
       case ESCAPED_STRICT_RESERVED_WORD:
       case FUTURE_STRICT_RESERVED_WORD:

test/cctest/test-parsing.cc

@@ -1508,7 +1508,8 @@ enum ParserFlag {
   kAllowHarmonyFunctionSent,
   kAllowHarmonyRestrictiveDeclarations,
   kAllowHarmonyExponentiationOperator,
-  kAllowHarmonyForIn
+  kAllowHarmonyForIn,
+  kAllowHarmonyAsyncAwait
 };
 
 enum ParserSyncTestResult {
@@ -1529,6 +1530,8 @@ void SetParserFlags(i::ParserBase<Traits>* parser,
   parser->set_allow_harmony_exponentiation_operator(
       flags.Contains(kAllowHarmonyExponentiationOperator));
   parser->set_allow_harmony_for_in(flags.Contains(kAllowHarmonyForIn));
+  parser->set_allow_harmony_async_await(
+      flags.Contains(kAllowHarmonyAsyncAwait));
 }
 
 
@@ -7448,6 +7451,234 @@ TEST(ExponentiationOperatorErrors) {
                     arraysize(always_flags));
 }
 
+TEST(AsyncAwait) {
+  // clang-format off
+  const char* context_data[][2] = {
+    { "'use strict';", "" },
+    { "", "" },
+    { NULL, NULL }
+  };
+
+  const char* data[] = {
+    "var asyncFn = async function() { await 1; };",
+    "var asyncFn = async function withName() { await 1; };",
+    "var asyncFn = async () => await 'test';",
+    "var asyncFn = async x => await x + 'test';",
+    "async function asyncFn() { await 1; }",
+    "var O = { async method() { await 1; } }",
+    "var O = { async ['meth' + 'od']() { await 1; } }",
+    "var O = { async 'method'() { await 1; } }",
+    "var O = { async 0() { await 1; } }",
+    "async function await() {}",
+    NULL
+  };
+  // clang-format on
+
+  static const ParserFlag always_flags[] = {kAllowHarmonyAsyncAwait};
+  RunParserSyncTest(context_data, data, kSuccess, NULL, 0, always_flags,
+                    arraysize(always_flags));
+
+  // clang-format off
+  const char* async_body_context_data[][2] = {
+    { "async function f() {", "}" },
+    { "var f = async function() {", "}" },
+    { "var f = async() => {", "}" },
+    { "var O = { async method() {", "} }" },
+    { "'use strict'; async function f() {", "}" },
+    { "'use strict'; var f = async function() {", "}" },
+    { "'use strict'; var f = async() => {", "}" },
+    { "'use strict'; var O = { async method() {", "} }" },
+    { NULL, NULL }
+  };
+
+  const char* body_context_data[][2] = {
+    { "function f() {", "}" },
+    { "function* g() {", "}" },
+    { "var f = function() {", "}" },
+    { "var g = function*() {", "}" },
+    { "var O = { method() {", "} }" },
+    { "var O = { *method() {", "} }" },
+    { "var f = () => {", "}" },
+    { "'use strict'; function f() {", "}" },
+    { "'use strict'; function* g() {", "}" },
+    { "'use strict'; var f = function() {", "}" },
+    { "'use strict'; var g = function*() {", "}" },
+    { "'use strict'; var O = { method() {", "} }" },
+    { "'use strict'; var O = { *method() {", "} }" },
+    { "'use strict'; var f = () => {", "}" },
+    { NULL, NULL }
+  };
+
+  const char* body_data[] = {
+    "var async = 1; return async;",
+    "let async = 1; return async;",
+    "const async = 1; return async;",
+    "function async() {} return async();",
+    "var async = async => async; return async();",
+    "function foo() { var await = 1; return await; }",
+    "function foo(await) { return await; }",
+    "function* foo() { var await = 1; return await; }",
+    "function* foo(await) { return await; }",
+    "var f = (await) => await;",
+    "var f = () => { var await = 1; return await; }",
+    "var O = { method() { var await = 1; return await; } };",
+    "var O = { method(await) { return await; } };",
+    "var O = { *method() { var await = 1; return await; } };",
+    "var O = { *method(await) { return await; } };",
+
+    "(function await() {})",
+    NULL
+  };
+  // clang-format on
+
+  RunParserSyncTest(async_body_context_data, body_data, kSuccess, NULL, 0,
+                    always_flags, arraysize(always_flags));
+  RunParserSyncTest(body_context_data, body_data, kSuccess, NULL, 0,
+                    always_flags, arraysize(always_flags));
+}
+
+TEST(AsyncAwaitErrors) {
+  // clang-format off
+  const char* context_data[][2] = {
+    { "'use strict';", "" },
+    { "", "" },
+    { NULL, NULL }
+  };
+
+  const char* strict_context_data[][2] = {
+    { "'use strict';", "" },
+    { NULL, NULL }
+  };
+
+  const char* error_data[] = {
+    "var asyncFn = async function() { var await = 1; };",
+    "var asyncFn = async function() { var { await } = 1; };",
+    "var asyncFn = async function() { var [ await ] = 1; };",
+    "var asyncFn = async function await() {};",
+    "var asyncFn = async () => var await = 'test';",
+    "var asyncFn = async await => await + 'test';",
+    "var asyncFn = async function(await) {};",
+    "var asyncFn = async function() { return async (await) => {}; }",
+    "var asyncFn = async (await) => 'test';",
+    "var asyncFn = async x => { var await = 1; }",
+    "var asyncFn = async x => { var { await } = 1; }",
+    "var asyncFn = async x => { var [ await ] = 1; }",
+    "async function f(await) {}",
+    "async function f() { var await = 1; }",
+    "async function f() { var { await } = 1; }",
+    "async function f() { var [ await ] = 1; }",
+
+    "var O = { async method(a, a) {} }",
+    "var O = { async ['meth' + 'od'](a, a) {} }",
+    "var O = { async 'method'(a, a) {} }",
+    "var O = { async 0(a, a) {} }",
+
+    "async function f() { var O = { async [await](a, a) {} } }",
+
+    "var asyncFn = async function() { await; }",
+    "async function f() { await; }",
+    "var O = { async method() { await; } };",
+    "var f = async() => await;",
+    "var f = async() => { await; };",
+
+    "var asyncFn = async function*() {}",
+    "async function* f() {}",
+    "var O = { *async method() {} };",
+    "var O = { async *method() {} };",
+    "var O = { async method*() {} };",
+
+    "var asyncFn = async function(x = await 1) { return x; }",
+    "async function f(x = await 1) { return x; }",
+    "var f = async(x = await 1) => x;",
+    "var O = { async method(x = await 1) { return x; } };",
+
+    "var f = async(x = await) => 1;",
+
+    "class C { async constructor() {} }",
+    "class C {}; class C2 extends C { async constructor() {} }",
+    "class C { static async prototype() {} }",
+    "class C {}; class C2 extends C { static async prototype() {} }",
+
+    "var f = async() => ((async(x = await 1) => x)();",
+
+    "var asyncFn = async function() { function await() {} }",
+    "var asyncFn = async() => { function await() {} }",
+    "var O = { async method() { function await() {} } }",
+    "async function foo() { function await() {} }",
+
+    NULL
+  };
+
+  const char* strict_error_data[] = {
+    "var O = { async method(eval) {} }",
+    "var O = { async ['meth' + 'od'](eval) {} }",
+    "var O = { async 'method'(eval) {} }",
+    "var O = { async 0(eval) {} }",
+
+    "var O = { async method(arguments) {} }",
+    "var O = { async ['meth' + 'od'](arguments) {} }",
+    "var O = { async 'method'(arguments) {} }",
+    "var O = { async 0(arguments) {} }",
+
+    "var O = { async method(dupe, dupe) {} }",
+
+    // TODO(caitp): preparser needs to report duplicate parameter errors, too.
+    // "var f = async(dupe, dupe) => {}",
+
+    NULL
+  };
+  // clang-format on
+
+  static const ParserFlag always_flags[] = {kAllowHarmonyAsyncAwait};
+  RunParserSyncTest(context_data, error_data, kError, NULL, 0, always_flags,
+                    arraysize(always_flags));
+  RunParserSyncTest(strict_context_data, strict_error_data, kError, NULL, 0,
+                    always_flags, arraysize(always_flags));
+}
+
+TEST(AsyncAwaitModule) {
+  // clang-format off
+  const char* context_data[][2] = {
+    { "", "" },
+    { NULL, NULL }
+  };
+
+  const char* data[] = {
+    "export default async function() { await 1; }",
+    "export default async function async() { await 1; }",
+    "export async function async() { await 1; }",
+    NULL
+  };
+  // clang-format on
+
+  static const ParserFlag always_flags[] = {kAllowHarmonyAsyncAwait};
+  RunModuleParserSyncTest(context_data, data, kSuccess, NULL, 0, always_flags,
+                          arraysize(always_flags), NULL, 0, false);
+}
+
+TEST(AsyncAwaitModuleErrors) {
+  // clang-format off
+  const char* context_data[][2] = {
+    { "", "" },
+    { NULL, NULL }
+  };
+
+  const char* error_data[] = {
+    "export default (async function await() {})",
+    "export default async function await() {}",
+    "export async function await() {}",
+    "export async function() {}",
+    "export async",
+    NULL
+  };
+  // clang-format on
+
+  static const ParserFlag always_flags[] = {kAllowHarmonyAsyncAwait};
+  RunModuleParserSyncTest(context_data, error_data, kError, NULL, 0,
+                          always_flags, arraysize(always_flags), NULL, 0,
+                          false);
+}
+
 TEST(RestrictiveForInErrors) {
   // clang-format off
   const char* context_data[][2] = {