[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) |
+        FunctionTypeBits::encode(function_type) | Pretenure::encode(false) |
-        IsNamedExpression::encode(function_type == kNamedExpression) |
-        IsAnonymousExpression::encode(function_type == kAnonymousExpression) |
-        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 FunctionTypeBits : public BitField16<FunctionType, 0, 2> {};
-  class IsNamedExpression : public BitField16<bool, 1, 1> {};
+  class Pretenure : public BitField16<bool, 2, 1> {};
-  class IsAnonymousExpression : public BitField16<bool, 2, 1> {};
+  class HasDuplicateParameters : public BitField16<bool, 3, 1> {};
-  class Pretenure : public BitField16<bool, 3, 1> {};
+  class IsFunction : public BitField16<bool, 4, 1> {};
-  class HasDuplicateParameters : public BitField16<bool, 4, 1> {};
+  class ShouldEagerCompile : public BitField16<bool, 5, 1> {};
-  class IsFunction : public BitField16<bool, 5, 1> {};
+  class ShouldBeUsedOnceHint : public BitField16<bool, 6, 1> {};
-  class ShouldEagerCompile : public BitField16<bool, 6, 1> {};
+  class FunctionKindBits : public BitField16<FunctionKind, 7, 9> {};
-  class ShouldBeUsedOnceHint : public BitField16<bool, 7, 1> {};
-  class FunctionKindBits : public BitField16<FunctionKind, 8, 8> {};
 
   // 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)                                  \
+#define HARMONY_INPROGRESS(V)                                           \
-  V(harmony_function_sent, "harmony function.sent")            \
+  V(harmony_function_sent, "harmony function.sent")                     \
-  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")    \
+  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")             \
-  V(harmony_simd, "harmony simd")                              \
+  V(harmony_simd, "harmony simd")                                       \
-  V(harmony_do_expressions, "harmony do-expressions")          \
+  V(harmony_do_expressions, "harmony do-expressions")                   \
-  V(harmony_regexp_property, "harmony unicode regexp property classes")
+  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 |
+    PatternProductions =
-                          AssignmentPatternProduction | LetPatternProduction),
+        (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-base.h

@@ -29,6 +29,86 @@ enum AllowLabelledFunctionStatement {
   kDisallowLabelledFunctionStatement,
 };
 
+enum class FunctionBody { Normal, SingleExpression };
+
+enum class ParseFunctionFlags {
+  kIsNormal = 0,
+  kIsGenerator = 1,
+  kIsAsync = 2,
+  kIsDefault = 4
+};
+
+static inline ParseFunctionFlags operator|(ParseFunctionFlags lhs,
+                                           ParseFunctionFlags rhs) {
+  typedef unsigned char T;
+  return static_cast<ParseFunctionFlags>(static_cast<T>(lhs) |
+                                         static_cast<T>(rhs));
+}
+
+static inline ParseFunctionFlags& operator|=(ParseFunctionFlags& lhs,
+                                             const ParseFunctionFlags& rhs) {
+  lhs = lhs | rhs;
+  return lhs;
+}
+
+static inline bool operator&(ParseFunctionFlags bitfield,
+                             ParseFunctionFlags mask) {
+  typedef unsigned char T;
+  return static_cast<T>(bitfield) & static_cast<T>(mask);
+}
+
+enum class MethodKind {
+  Normal = 0,
+  Static = 1 << 0,
+  Generator = 1 << 1,
+  StaticGenerator = Static | Generator,
+  Async = 1 << 2,
+  StaticAsync = Static | Async,
+
+  /* Any non-ordinary method kinds */
+  SpecialMask = Generator | Async
+};
+
+inline bool IsValidMethodKind(MethodKind kind) {
+  return kind == MethodKind::Normal || kind == MethodKind::Static ||
+         kind == MethodKind::Generator || kind == MethodKind::StaticGenerator ||
+         kind == MethodKind::Async || kind == MethodKind::StaticAsync;
+}
+
+static inline MethodKind operator|(MethodKind lhs, MethodKind rhs) {
+  typedef unsigned char T;
+  return static_cast<MethodKind>(static_cast<T>(lhs) | static_cast<T>(rhs));
+}
+
+static inline MethodKind& operator|=(MethodKind& lhs, const MethodKind& rhs) {
+  lhs = lhs | rhs;
+  DCHECK(IsValidMethodKind(lhs));
+  return lhs;
+}
+
+static inline bool operator&(MethodKind bitfield, MethodKind mask) {
+  typedef unsigned char T;
+  return static_cast<T>(bitfield) & static_cast<T>(mask);
+}
+
+inline bool IsNormalMethod(MethodKind kind) {
+  return kind == MethodKind::Normal;
+}
+
+inline bool IsSpecialMethod(MethodKind kind) {
+  return kind & MethodKind::SpecialMask;
+}
+
+inline bool IsStaticMethod(MethodKind kind) {
+  return kind & MethodKind::Static;
+}
+
+inline bool IsGeneratorMethod(MethodKind kind) {
+  return kind & MethodKind::Generator;
+}
+
+inline bool IsAsyncMethod(MethodKind kind) { return kind & MethodKind::Async; }
+
 struct FormalParametersBase {
   explicit FormalParametersBase(Scope* scope) : scope(scope) {}
   Scope* scope;
@@ -117,7 +197,8 @@ class ParserBase : public Traits {
         allow_harmony_do_expressions_(false),
         allow_harmony_for_in_(false),
         allow_harmony_function_name_(false),
-        allow_harmony_function_sent_(false) {}
+        allow_harmony_function_sent_(false),
+        allow_harmony_async_await_(false) {}
 
 #define ALLOW_ACCESSORS(name)                           \
   bool allow_##name() const { return allow_##name##_; } \
@@ -137,6 +218,7 @@ class ParserBase : public Traits {
   ALLOW_ACCESSORS(harmony_for_in);
   ALLOW_ACCESSORS(harmony_function_name);
   ALLOW_ACCESSORS(harmony_function_sent);
+  ALLOW_ACCESSORS(harmony_async_await);
   SCANNER_ACCESSORS(harmony_exponentiation_operator);
 
 #undef SCANNER_ACCESSORS
@@ -284,6 +366,8 @@ class ParserBase : public Traits {
     }
 
     bool is_generator() const { return IsGeneratorFunction(kind_); }
+    bool is_async_function() const { return IsAsyncFunction(kind_); }
+    bool is_resumable() const { return is_generator() || is_async_function(); }
 
     FunctionKind kind() const { return kind_; }
     FunctionState* outer() const { return outer_function_state_; }
@@ -291,7 +375,7 @@ class ParserBase : public Traits {
     void set_generator_object_variable(
         typename Traits::Type::GeneratorVariable* variable) {
       DCHECK(variable != NULL);
-      DCHECK(is_generator());
+      DCHECK(is_resumable());
       generator_object_variable_ = variable;
     }
     typename Traits::Type::GeneratorVariable* generator_object_variable()
@@ -576,9 +660,10 @@ class ParserBase : public Traits {
 
   bool peek_any_identifier() {
     Token::Value next = peek();
-    return next == Token::IDENTIFIER || next == Token::AWAIT ||
+    return next == Token::IDENTIFIER || next == Token::ENUM ||
-           next == Token::ENUM || next == Token::FUTURE_STRICT_RESERVED_WORD ||
+           next == Token::AWAIT || next == Token::ASYNC ||
-           next == Token::LET || next == Token::STATIC || next == Token::YIELD;
+           next == Token::FUTURE_STRICT_RESERVED_WORD || next == Token::LET ||
+           next == Token::STATIC || next == Token::YIELD;
   }
 
   bool CheckContextualKeyword(Vector<const char> keyword) {
@@ -684,6 +769,10 @@ class ParserBase : public Traits {
 
   LanguageMode language_mode() { return scope_->language_mode(); }
   bool is_generator() const { return function_state_->is_generator(); }
+  bool is_async_function() const {
+    return function_state_->is_async_function();
+  }
+  bool is_resumable() const { return function_state_->is_resumable(); }
 
   // Report syntax errors.
   void ReportMessage(MessageTemplate::Template message, const char* arg = NULL,
@@ -740,8 +829,16 @@ class ParserBase : public Traits {
 
   void ValidateBindingPattern(const ExpressionClassifier* classifier,
                               bool* ok) {
-    if (!classifier->is_valid_binding_pattern()) {
+    if (!classifier->is_valid_binding_pattern() ||
-      ReportClassifierError(classifier->binding_pattern_error());
+        !classifier->is_valid_async_binding_pattern()) {
+      const Scanner::Location& a = classifier->binding_pattern_error().location;
+      const Scanner::Location& b =
+          classifier->async_binding_pattern_error().location;
+      if (a.beg_pos < 0 || (b.beg_pos >= 0 && a.beg_pos > b.beg_pos)) {
+        ReportClassifierError(classifier->async_binding_pattern_error());
+      } else {
+        ReportClassifierError(classifier->binding_pattern_error());
+      }
       *ok = false;
     }
   }
@@ -770,7 +867,8 @@ class ParserBase : public Traits {
 
   void ValidateArrowFormalParameters(const ExpressionClassifier* classifier,
                                      ExpressionT expr,
-                                     bool parenthesized_formals, bool* ok) {
+                                     bool parenthesized_formals, bool is_async,
+                                     bool* ok) {
     if (classifier->is_valid_binding_pattern()) {
       // A simple arrow formal parameter: IDENTIFIER => BODY.
       if (!this->IsIdentifier(expr)) {
@@ -790,6 +888,12 @@ class ParserBase : public Traits {
       ReportClassifierError(error);
       *ok = false;
     }
+    if (is_async && !classifier->is_valid_async_arrow_formal_parameters()) {
+      const typename ExpressionClassifier::Error& error =
+          classifier->async_arrow_formal_parameters_error();
+      ReportClassifierError(error);
+      *ok = false;
+    }
   }
 
   void ValidateLetPattern(const ExpressionClassifier* classifier, bool* ok) {
@@ -863,22 +967,32 @@ class ParserBase : public Traits {
                                  ExpressionClassifier* classifier, bool* ok);
 
   ExpressionT ParsePrimaryExpression(ExpressionClassifier* classifier,
-                                     bool* ok);
+                                     bool* is_async, bool* ok);
+  ExpressionT ParsePrimaryExpression(ExpressionClassifier* classifier,
+                                     bool* ok) {
+    bool is_async;
+    return ParsePrimaryExpression(classifier, &is_async, ok);
+  }
   ExpressionT ParseExpression(bool accept_IN, bool* ok);
   ExpressionT ParseExpression(bool accept_IN, ExpressionClassifier* classifier,
                               bool* ok);
   ExpressionT ParseArrayLiteral(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParsePropertyName(IdentifierT* name, bool* is_get, bool* is_set,
-                                bool* is_computed_name,
+                                bool* is_await, bool* is_computed_name,
                                 ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseObjectLiteral(ExpressionClassifier* classifier, bool* ok);
   ObjectLiteralPropertyT ParsePropertyDefinition(
       ObjectLiteralCheckerBase* checker, bool in_class, bool has_extends,
-      bool is_static, bool* is_computed_name, bool* has_seen_constructor,
+      MethodKind kind, bool* is_computed_name, bool* has_seen_constructor,
       ExpressionClassifier* classifier, IdentifierT* name, bool* ok);
+  typename Traits::Type::ExpressionList ParseArguments(
+      Scanner::Location* first_spread_pos, bool maybe_arrow,
+      ExpressionClassifier* classifier, bool* ok);
   typename Traits::Type::ExpressionList ParseArguments(
       Scanner::Location* first_spread_pos, ExpressionClassifier* classifier,
-      bool* ok);
+      bool* ok) {
+    return ParseArguments(first_spread_pos, false, classifier, ok);
+  }
 
   ExpressionT ParseAssignmentExpression(bool accept_IN,
                                         ExpressionClassifier* classifier,
@@ -898,12 +1012,15 @@ class ParserBase : public Traits {
   ExpressionT ParseLeftHandSideExpression(ExpressionClassifier* classifier,
                                           bool* ok);
   ExpressionT ParseMemberWithNewPrefixesExpression(
-      ExpressionClassifier* classifier, bool* ok);
+      ExpressionClassifier* classifier, bool* is_async, bool* ok);
-  ExpressionT ParseMemberExpression(ExpressionClassifier* classifier, bool* ok);
+  ExpressionT ParseMemberExpression(ExpressionClassifier* classifier,
+                                    bool* is_async, bool* ok);
   ExpressionT ParseMemberExpressionContinuation(
-      ExpressionT expression, ExpressionClassifier* classifier, bool* ok);
+      ExpressionT expression, bool* is_async, ExpressionClassifier* classifier,
+      bool* ok);
   ExpressionT ParseArrowFunctionLiteral(bool accept_IN,
                                         const FormalParametersT& parameters,
+                                        bool is_async,
                                         const ExpressionClassifier& classifier,
                                         bool* ok);
   ExpressionT ParseTemplateLiteral(ExpressionT tag, int start,
@@ -975,7 +1092,7 @@ class ParserBase : public Traits {
     explicit ObjectLiteralCheckerBase(ParserBase* parser) : parser_(parser) {}
 
     virtual void CheckProperty(Token::Value property, PropertyKind type,
-                               bool is_static, bool is_generator, bool* ok) = 0;
+                               MethodKind method_type, bool* ok) = 0;
 
     virtual ~ObjectLiteralCheckerBase() {}
 
@@ -993,8 +1110,8 @@ class ParserBase : public Traits {
     explicit ObjectLiteralChecker(ParserBase* parser)
         : ObjectLiteralCheckerBase(parser), has_seen_proto_(false) {}
 
-    void CheckProperty(Token::Value property, PropertyKind type, bool is_static,
+    void CheckProperty(Token::Value property, PropertyKind type,
-                       bool is_generator, bool* ok) override;
+                       MethodKind method_type, bool* ok) override;
 
    private:
     bool IsProto() { return this->scanner()->LiteralMatches("__proto__", 9); }
@@ -1008,8 +1125,8 @@ class ParserBase : public Traits {
     explicit ClassLiteralChecker(ParserBase* parser)
         : ObjectLiteralCheckerBase(parser), has_seen_constructor_(false) {}
 
-    void CheckProperty(Token::Value property, PropertyKind type, bool is_static,
+    void CheckProperty(Token::Value property, PropertyKind type,
-                       bool is_generator, bool* ok) override;
+                       MethodKind method_type, bool* ok) override;
 
    private:
     bool IsConstructor() {
@@ -1046,6 +1163,7 @@ class ParserBase : public Traits {
   bool allow_harmony_for_in_;
   bool allow_harmony_function_name_;
   bool allow_harmony_function_sent_;
+  bool allow_harmony_async_await_;
 };
 
 template <class Traits>
@@ -1181,7 +1299,8 @@ typename ParserBase<Traits>::IdentifierT
 ParserBase<Traits>::ParseAndClassifyIdentifier(ExpressionClassifier* classifier,
                                                bool* ok) {
   Token::Value next = Next();
-  if (next == Token::IDENTIFIER || (next == Token::AWAIT && !parsing_module_)) {
+  if (next == Token::IDENTIFIER || next == Token::ASYNC ||
+      (next == Token::AWAIT && !parsing_module_)) {
     IdentifierT name = this->GetSymbol(scanner());
     // When this function is used to read a formal parameter, we don't always
     // know whether the function is going to be strict or sloppy.  Indeed for
@@ -1206,6 +1325,14 @@ ParserBase<Traits>::ParseAndClassifyIdentifier(ExpressionClassifier* classifier,
             scanner()->location(), MessageTemplate::kStrictEvalArguments);
       }
     }
+    if (this->IsAwait(name)) {
+      if (is_async_function()) {
+        classifier->RecordPatternError(
+            scanner()->location(), MessageTemplate::kAwaitBindingIdentifier);
+      }
+      classifier->RecordAsyncArrowFormalParametersError(
+          scanner()->location(), MessageTemplate::kAwaitBindingIdentifier);
+    }
 
     if (classifier->duplicate_finder() != nullptr &&
         scanner()->FindSymbol(classifier->duplicate_finder(), 1) != 0) {
@@ -1245,7 +1372,8 @@ typename ParserBase<Traits>::IdentifierT
 ParserBase<Traits>::ParseIdentifierOrStrictReservedWord(
     bool is_generator, bool* is_strict_reserved, bool* ok) {
   Token::Value next = Next();
-  if (next == Token::IDENTIFIER || (next == Token::AWAIT && !parsing_module_)) {
+  if (next == Token::IDENTIFIER || (next == Token::AWAIT && !parsing_module_) ||
+      next == Token::ASYNC) {
     *is_strict_reserved = false;
   } else if (next == Token::FUTURE_STRICT_RESERVED_WORD || next == Token::LET ||
              next == Token::STATIC || (next == Token::YIELD && !is_generator)) {
@@ -1265,9 +1393,10 @@ template <class Traits>
 typename ParserBase<Traits>::IdentifierT
 ParserBase<Traits>::ParseIdentifierName(bool* ok) {
   Token::Value next = Next();
-  if (next != Token::IDENTIFIER && next != Token::ENUM &&
+  if (next != Token::IDENTIFIER && next != Token::ASYNC &&
-      next != Token::AWAIT && next != Token::LET && next != Token::STATIC &&
+      next != Token::ENUM && next != Token::AWAIT && next != Token::LET &&
-      next != Token::YIELD && next != Token::FUTURE_STRICT_RESERVED_WORD &&
+      next != Token::STATIC && next != Token::YIELD &&
+      next != Token::FUTURE_STRICT_RESERVED_WORD &&
       next != Token::ESCAPED_KEYWORD &&
       next != Token::ESCAPED_STRICT_RESERVED_WORD && !Token::IsKeyword(next)) {
     this->ReportUnexpectedToken(next);
@@ -1321,11 +1450,10 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseRegExpLiteral(
 #define DUMMY )  // to make indentation work
 #undef DUMMY
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
-                                           bool* ok) {
+                                           bool* is_async, bool* ok) {
   // PrimaryExpression ::
   //   'this'
   //   'null'
@@ -1341,6 +1469,7 @@ ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
   //   '(' Expression ')'
   //   TemplateLiteral
   //   do Block
+  //   AsyncFunctionExpression
 
   int beg_pos = peek_position();
   switch (peek()) {
@@ -1360,6 +1489,16 @@ ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
       BindingPatternUnexpectedToken(classifier);
       return this->ExpressionFromLiteral(Next(), beg_pos, scanner(), factory());
 
+    case Token::ASYNC:
+      if (allow_harmony_async_await() &&
+          !scanner()->HasAnyLineTerminatorAfterNext() &&
+          PeekAhead() == Token::FUNCTION) {
+        Consume(Token::ASYNC);
+        return this->ParseAsyncFunctionExpression(CHECK_OK);
+      }
+      // CoverCallExpressionAndAsyncArrowHead
+      *is_async = true;
+    /* falls through */
     case Token::IDENTIFIER:
     case Token::LET:
     case Token::STATIC:
@@ -1631,11 +1770,10 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseArrayLiteral(
   return result;
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParsePropertyName(
-    IdentifierT* name, bool* is_get, bool* is_set, bool* is_computed_name,
+    IdentifierT* name, bool* is_get, bool* is_set, bool* is_await,
-    ExpressionClassifier* classifier, bool* ok) {
+    bool* is_computed_name, ExpressionClassifier* classifier, bool* ok) {
   Token::Value token = peek();
   int pos = peek_position();
 
@@ -1680,6 +1818,9 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParsePropertyName(
     default:
       *name = ParseIdentifierName(CHECK_OK);
       scanner()->IsGetOrSet(is_get, is_set);
+      if (this->IsAwait(*name)) {
+        *is_await = true;
+      }
       break;
   }
 
@@ -1689,38 +1830,50 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParsePropertyName(
              : factory()->NewStringLiteral(*name, pos);
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ObjectLiteralPropertyT
 ParserBase<Traits>::ParsePropertyDefinition(
     ObjectLiteralCheckerBase* checker, bool in_class, bool has_extends,
-    bool is_static, bool* is_computed_name, bool* has_seen_constructor,
+    MethodKind method_kind, bool* is_computed_name, bool* has_seen_constructor,
     ExpressionClassifier* classifier, IdentifierT* name, bool* ok) {
-  DCHECK(!in_class || is_static || has_seen_constructor != nullptr);
+  DCHECK(!in_class || IsStaticMethod(method_kind) ||
+         has_seen_constructor != nullptr);
   ExpressionT value = this->EmptyExpression();
   bool is_get = false;
   bool is_set = false;
+  bool is_await = false;
   bool is_generator = Check(Token::MUL);
+  bool is_async = false;
+  const bool is_static = IsStaticMethod(method_kind);
 
   Token::Value name_token = peek();
+
+  if (is_generator) {
+    method_kind |= MethodKind::Generator;
+  } else if (allow_harmony_async_await() && name_token == Token::ASYNC &&
+             !scanner()->HasAnyLineTerminatorAfterNext() &&
+             PeekAhead() != Token::LPAREN && PeekAhead()) {
+    is_async = true;
+  }
+
   int next_beg_pos = scanner()->peek_location().beg_pos;
   int next_end_pos = scanner()->peek_location().end_pos;
-  ExpressionT name_expression =
+  ExpressionT name_expression = ParsePropertyName(
-      ParsePropertyName(name, &is_get, &is_set, is_computed_name, classifier,
+      name, &is_get, &is_set, &is_await, is_computed_name, classifier,
-                        CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
+      CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
 
   if (fni_ != nullptr && !*is_computed_name) {
     this->PushLiteralName(fni_, *name);
   }
 
   if (!in_class && !is_generator) {
-    DCHECK(!is_static);
+    DCHECK(!IsStaticMethod(method_kind));
 
     if (peek() == Token::COLON) {
       // PropertyDefinition
       //    PropertyName ':' AssignmentExpression
       if (!*is_computed_name) {
-        checker->CheckProperty(name_token, kValueProperty, false, false,
+        checker->CheckProperty(name_token, kValueProperty, MethodKind::Normal,
                                CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
       }
       Consume(Token::COLON);
@@ -1730,8 +1883,8 @@ ParserBase<Traits>::ParsePropertyDefinition(
       CheckDestructuringElement(value, classifier, beg_pos,
                                 scanner()->location().end_pos);
 
-      return factory()->NewObjectLiteralProperty(name_expression, value, false,
+      return factory()->NewObjectLiteralProperty(name_expression, value,
-                                                 *is_computed_name);
+                                                 is_static, *is_computed_name);
     }
 
     if (Token::IsIdentifier(name_token, language_mode(), this->is_generator(),
@@ -1752,7 +1905,11 @@ ParserBase<Traits>::ParsePropertyDefinition(
         classifier->RecordLetPatternError(
             scanner()->location(), MessageTemplate::kLetInLexicalBinding);
       }
-
+      if (is_await && is_async_function()) {
+        classifier->RecordPatternError(
+            Scanner::Location(next_beg_pos, next_end_pos),
+            MessageTemplate::kAwaitBindingIdentifier);
+      }
       ExpressionT lhs = this->ExpressionFromIdentifier(
           *name, next_beg_pos, next_end_pos, scope_, factory());
       CheckDestructuringElement(lhs, classifier, next_beg_pos, next_end_pos);
@@ -1780,7 +1937,7 @@ ParserBase<Traits>::ParsePropertyDefinition(
       }
 
       return factory()->NewObjectLiteralProperty(
-          name_expression, value, ObjectLiteralProperty::COMPUTED, false,
+          name_expression, value, ObjectLiteralProperty::COMPUTED, is_static,
           false);
     }
   }
@@ -1790,20 +1947,32 @@ ParserBase<Traits>::ParsePropertyDefinition(
       Scanner::Location(next_beg_pos, scanner()->location().end_pos),
       MessageTemplate::kInvalidDestructuringTarget);
 
+  if (is_async && !IsSpecialMethod(method_kind)) {
+    DCHECK(!is_get);
+    DCHECK(!is_set);
+    bool dont_care;
+    name_expression = ParsePropertyName(
+        name, &dont_care, &dont_care, &dont_care, is_computed_name, classifier,
+        CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
+    method_kind |= MethodKind::Async;
+  }
+
   if (is_generator || peek() == Token::LPAREN) {
     // MethodDefinition
     //    PropertyName '(' StrictFormalParameters ')' '{' FunctionBody '}'
     //    '*' PropertyName '(' StrictFormalParameters ')' '{' FunctionBody '}'
     if (!*is_computed_name) {
-      checker->CheckProperty(name_token, kMethodProperty, is_static,
+      checker->CheckProperty(name_token, kMethodProperty, method_kind,
-                             is_generator,
                              CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
     }
 
-    FunctionKind kind = is_generator ? FunctionKind::kConciseGeneratorMethod
+    FunctionKind kind = is_generator
-                                     : FunctionKind::kConciseMethod;
+                            ? FunctionKind::kConciseGeneratorMethod
+                            : is_async ? FunctionKind::kAsyncConciseMethod
+                                       : FunctionKind::kConciseMethod;
 
-    if (in_class && !is_static && this->IsConstructor(*name)) {
+    if (in_class && !IsStaticMethod(method_kind) &&
+        this->IsConstructor(*name)) {
       *has_seen_constructor = true;
       kind = has_extends ? FunctionKind::kSubclassConstructor
                          : FunctionKind::kBaseConstructor;
@@ -1819,13 +1988,13 @@ ParserBase<Traits>::ParsePropertyDefinition(
                                                is_static, *is_computed_name);
   }
 
-  if (in_class && name_token == Token::STATIC && !is_static) {
+  if (in_class && name_token == Token::STATIC && IsNormalMethod(method_kind)) {
     // ClassElement (static)
     //    'static' MethodDefinition
     *name = this->EmptyIdentifier();
     ObjectLiteralPropertyT property = ParsePropertyDefinition(
-        checker, true, has_extends, true, is_computed_name, nullptr, classifier,
+        checker, true, has_extends, MethodKind::Static, is_computed_name,
-        name, ok);
+        nullptr, classifier, name, ok);
     Traits::RewriteNonPattern(classifier, ok);
     return property;
   }
@@ -1839,12 +2008,11 @@ ParserBase<Traits>::ParsePropertyDefinition(
     name_token = peek();
 
     name_expression = ParsePropertyName(
-        name, &dont_care, &dont_care, is_computed_name, classifier,
+        name, &dont_care, &dont_care, &dont_care, is_computed_name, classifier,
         CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
 
     if (!*is_computed_name) {
-      checker->CheckProperty(name_token, kAccessorProperty, is_static,
+      checker->CheckProperty(name_token, kAccessorProperty, method_kind,
-                             is_generator,
                              CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
     }
 
@@ -1894,13 +2062,12 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseObjectLiteral(
     FuncNameInferrer::State fni_state(fni_);
 
     const bool in_class = false;
-    const bool is_static = false;
     const bool has_extends = false;
     bool is_computed_name = false;
     IdentifierT name = this->EmptyIdentifier();
     ObjectLiteralPropertyT property = this->ParsePropertyDefinition(
-        &checker, in_class, has_extends, is_static, &is_computed_name, NULL,
+        &checker, in_class, has_extends, MethodKind::Normal, &is_computed_name,
-        classifier, &name, CHECK_OK);
+        NULL, classifier, &name, CHECK_OK);
 
     if (is_computed_name) {
       has_computed_names = true;
@@ -1934,11 +2101,10 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseObjectLiteral(
                                      pos);
 }
 
-
 template <class Traits>
 typename Traits::Type::ExpressionList ParserBase<Traits>::ParseArguments(
-    Scanner::Location* first_spread_arg_loc, ExpressionClassifier* classifier,
+    Scanner::Location* first_spread_arg_loc, bool maybe_arrow,
-    bool* ok) {
+    ExpressionClassifier* classifier, bool* ok) {
   // Arguments ::
   //   '(' (AssignmentExpression)*[','] ')'
 
@@ -1994,7 +2160,7 @@ typename Traits::Type::ExpressionList ParserBase<Traits>::ParseArguments(
   }
   *first_spread_arg_loc = spread_arg;
 
-  if (spread_arg.IsValid()) {
+  if ((!maybe_arrow || peek() != Token::ARROW) && spread_arg.IsValid()) {
     // Unspread parameter sequences are translated into array literals in the
     // parser. Ensure that the number of materialized literals matches between
     // the parser and preparser
@@ -2026,18 +2192,31 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
   ParserBase<Traits>::Checkpoint checkpoint(this);
   ExpressionClassifier arrow_formals_classifier(this,
                                                 classifier->duplicate_finder());
+
+  bool is_async = allow_harmony_async_await() && peek() == Token::ASYNC &&
+                  !scanner()->HasAnyLineTerminatorAfterNext();
+
   bool parenthesized_formals = peek() == Token::LPAREN;
-  if (!parenthesized_formals) {
+  if (!is_async && !parenthesized_formals) {
     ArrowFormalParametersUnexpectedToken(&arrow_formals_classifier);
   }
   ExpressionT expression = this->ParseConditionalExpression(
       accept_IN, &arrow_formals_classifier, CHECK_OK);
+
+  if (is_async && peek_any_identifier() && PeekAhead() == Token::ARROW) {
+    // async Identifier => AsyncConciseBody
+    IdentifierT name =
+        ParseAndClassifyIdentifier(&arrow_formals_classifier, CHECK_OK);
+    expression = this->ExpressionFromIdentifier(
+        name, position(), scanner()->location().end_pos, scope_, factory());
+  }
+
   if (peek() == Token::ARROW) {
     classifier->RecordPatternError(scanner()->peek_location(),
                                    MessageTemplate::kUnexpectedToken,
                                    Token::String(Token::ARROW));
     ValidateArrowFormalParameters(&arrow_formals_classifier, expression,
-                                  parenthesized_formals, CHECK_OK);
+                                  parenthesized_formals, is_async, CHECK_OK);
     // This reads strangely, but is correct: it checks whether any
     // sub-expression of the parameter list failed to be a valid formal
     // parameter initializer. Since YieldExpressions are banned anywhere
@@ -2045,9 +2224,11 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
     // TODO(adamk): Rename "FormalParameterInitializerError" to refer to
     // "YieldExpression", which is its only use.
     ValidateFormalParameterInitializer(&arrow_formals_classifier, ok);
+
     Scanner::Location loc(lhs_beg_pos, scanner()->location().end_pos);
-    Scope* scope =
+    Scope* scope = this->NewScope(scope_, FUNCTION_SCOPE,
-        this->NewScope(scope_, FUNCTION_SCOPE, FunctionKind::kArrowFunction);
+                                  is_async ? FunctionKind::kAsyncArrowFunction
+                                           : FunctionKind::kArrowFunction);
     // Because the arrow's parameters were parsed in the outer scope, any
     // usage flags that might have been triggered there need to be copied
     // to the arrow scope.
@@ -2069,7 +2250,7 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
           duplicate_loc);
     }
     expression = this->ParseArrowFunctionLiteral(
-        accept_IN, parameters, arrow_formals_classifier, CHECK_OK);
+        accept_IN, parameters, is_async, arrow_formals_classifier, CHECK_OK);
 
     if (fni_ != nullptr) fni_->Infer();
 
@@ -2086,8 +2267,10 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
   classifier->Accumulate(
       &arrow_formals_classifier,
       ExpressionClassifier::StandardProductions |
-      ExpressionClassifier::FormalParametersProductions |
+          ExpressionClassifier::FormalParametersProductions |
-      ExpressionClassifier::CoverInitializedNameProduction,
+          ExpressionClassifier::CoverInitializedNameProduction |
+          ExpressionClassifier::AsyncArrowFormalParametersProduction |
+          ExpressionClassifier::AsyncBindingPatternProduction,
       false);
 
   if (!Token::IsAssignmentOp(peek())) {
@@ -2129,8 +2312,10 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
   CheckNoTailCallExpressions(&rhs_classifier, CHECK_OK);
   Traits::RewriteNonPattern(&rhs_classifier, CHECK_OK);
   classifier->Accumulate(
-      &rhs_classifier, ExpressionClassifier::ExpressionProductions |
+      &rhs_classifier,
-                       ExpressionClassifier::CoverInitializedNameProduction);
+      ExpressionClassifier::ExpressionProductions |
+          ExpressionClassifier::CoverInitializedNameProduction |
+          ExpressionClassifier::AsyncArrowFormalParametersProduction);
 
   // TODO(1231235): We try to estimate the set of properties set by
   // constructors. We define a new property whenever there is an
@@ -2401,6 +2586,7 @@ ParserBase<Traits>::ParseUnaryExpression(ExpressionClassifier* classifier,
   //   '-' UnaryExpression
   //   '~' UnaryExpression
   //   '!' UnaryExpression
+  //   [+Await] AwaitExpression[?Yield]
 
   Token::Value op = peek();
   if (Token::IsUnaryOp(op)) {
@@ -2448,6 +2634,40 @@ ParserBase<Traits>::ParseUnaryExpression(ExpressionClassifier* classifier,
                                         expression,
                                         position());
 
+  } else if (is_async_function() && peek() == Token::AWAIT) {
+    int beg_pos = peek_position();
+    switch (PeekAhead()) {
+      case Token::RPAREN:
+      case Token::RBRACK:
+      case Token::RBRACE:
+      case Token::ASSIGN:
+      case Token::COMMA: {
+        Next();
+        IdentifierT name = this->GetSymbol(scanner());
+
+        // Possibly async arrow formals --- record ExpressionError just in case.
+        ExpressionUnexpectedToken(classifier);
+        classifier->RecordAsyncBindingPatternError(
+            Scanner::Location(beg_pos, scanner()->location().end_pos),
+            MessageTemplate::kAwaitBindingIdentifier);
+        classifier->RecordAsyncArrowFormalParametersError(
+            Scanner::Location(beg_pos, scanner()->location().end_pos),
+            MessageTemplate::kAwaitBindingIdentifier);
+
+        return this->ExpressionFromIdentifier(
+            name, beg_pos, scanner()->location().end_pos, scope_, factory());
+      }
+      default:
+        break;
+    }
+    Consume(Token::AWAIT);
+
+    ExpressionT value = ParseUnaryExpression(classifier, CHECK_OK);
+
+    classifier->RecordFormalParameterInitializerError(
+        Scanner::Location(beg_pos, scanner()->location().end_pos),
+        MessageTemplate::kAwaitExpressionFormalParameter);
+    return Traits::RewriteAwaitExpression(value, beg_pos);
   } else {
     return this->ParsePostfixExpression(classifier, ok);
   }
@@ -2497,8 +2717,9 @@ ParserBase<Traits>::ParseLeftHandSideExpression(
     return this->ParseTailCallExpression(classifier, ok);
   }
 
-  ExpressionT result =
+  bool is_async = false;
-      this->ParseMemberWithNewPrefixesExpression(classifier, CHECK_OK);
+  ExpressionT result = this->ParseMemberWithNewPrefixesExpression(
+      classifier, &is_async, CHECK_OK);
 
   while (true) {
     switch (peek()) {
@@ -2518,13 +2739,12 @@ ParserBase<Traits>::ParseLeftHandSideExpression(
 
       case Token::LPAREN: {
         CheckNoTailCallExpressions(classifier, CHECK_OK);
+        int pos;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
-        ArrowFormalParametersUnexpectedToken(classifier);
-
-        int pos;
         if (scanner()->current_token() == Token::IDENTIFIER ||
-            scanner()->current_token() == Token::SUPER) {
+            scanner()->current_token() == Token::SUPER ||
+            scanner()->current_token() == Token::ASYNC) {
           // For call of an identifier we want to report position of
           // the identifier as position of the call in the stack trace.
           pos = position();
@@ -2544,7 +2764,18 @@ ParserBase<Traits>::ParseLeftHandSideExpression(
         }
         Scanner::Location spread_pos;
         typename Traits::Type::ExpressionList args =
-            ParseArguments(&spread_pos, classifier, CHECK_OK);
+            ParseArguments(&spread_pos, is_async, classifier, CHECK_OK);
+
+        if (V8_UNLIKELY(is_async && peek() == Token::ARROW)) {
+          if (args->length()) {
+            // async ( Arguments ) => ...
+            return Traits::ExpressionListToExpression(args);
+          }
+          // async () => ...
+          return factory()->NewEmptyParentheses(pos);
+        }
+
+        ArrowFormalParametersUnexpectedToken(classifier);
 
         // Keep track of eval() calls since they disable all local variable
         // optimizations.
@@ -2605,11 +2836,10 @@ ParserBase<Traits>::ParseLeftHandSideExpression(
   }
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseMemberWithNewPrefixesExpression(
-    ExpressionClassifier* classifier, bool* ok) {
+    ExpressionClassifier* classifier, bool* is_async, bool* ok) {
   // NewExpression ::
   //   ('new')+ MemberExpression
   //
@@ -2642,7 +2872,8 @@ ParserBase<Traits>::ParseMemberWithNewPrefixesExpression(
     } else if (peek() == Token::PERIOD) {
       return ParseNewTargetExpression(CHECK_OK);
     } else {
-      result = this->ParseMemberWithNewPrefixesExpression(classifier, CHECK_OK);
+      result = this->ParseMemberWithNewPrefixesExpression(classifier, is_async,
+                                                          CHECK_OK);
     }
     Traits::RewriteNonPattern(classifier, CHECK_OK);
     if (peek() == Token::LPAREN) {
@@ -2658,8 +2889,8 @@ ParserBase<Traits>::ParseMemberWithNewPrefixesExpression(
         result = factory()->NewCallNew(result, args, new_pos);
       }
       // The expression can still continue with . or [ after the arguments.
-      result =
+      result = this->ParseMemberExpressionContinuation(result, is_async,
-          this->ParseMemberExpressionContinuation(result, classifier, CHECK_OK);
+                                                       classifier, CHECK_OK);
       return result;
     }
     // NewExpression without arguments.
@@ -2667,14 +2898,13 @@ ParserBase<Traits>::ParseMemberWithNewPrefixesExpression(
                                  new_pos);
   }
   // No 'new' or 'super' keyword.
-  return this->ParseMemberExpression(classifier, ok);
+  return this->ParseMemberExpression(classifier, is_async, ok);
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseMemberExpression(ExpressionClassifier* classifier,
-                                          bool* ok) {
+                                          bool* is_async, bool* ok) {
   // MemberExpression ::
   //   (PrimaryExpression | FunctionLiteral | ClassLiteral)
   //     ('[' Expression ']' | '.' Identifier | Arguments | TemplateLiteral)*
@@ -2731,10 +2961,11 @@ ParserBase<Traits>::ParseMemberExpression(ExpressionClassifier* classifier,
     const bool is_new = false;
     result = ParseSuperExpression(is_new, classifier, CHECK_OK);
   } else {
-    result = ParsePrimaryExpression(classifier, CHECK_OK);
+    result = ParsePrimaryExpression(classifier, is_async, CHECK_OK);
   }
 
-  result = ParseMemberExpressionContinuation(result, classifier, CHECK_OK);
+  result =
+      ParseMemberExpressionContinuation(result, is_async, classifier, CHECK_OK);
   return result;
 }
 
@@ -2801,16 +3032,17 @@ ParserBase<Traits>::ParseNewTargetExpression(bool* ok) {
   return this->NewTargetExpression(scope_, factory(), pos);
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseMemberExpressionContinuation(
-    ExpressionT expression, ExpressionClassifier* classifier, bool* ok) {
+    ExpressionT expression, bool* is_async, ExpressionClassifier* classifier,
+    bool* ok) {
   // Parses this part of MemberExpression:
   // ('[' Expression ']' | '.' Identifier | TemplateLiteral)*
   while (true) {
     switch (peek()) {
       case Token::LBRACK: {
+        *is_async = false;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
         ArrowFormalParametersUnexpectedToken(classifier);
@@ -2827,6 +3059,7 @@ ParserBase<Traits>::ParseMemberExpressionContinuation(
         break;
       }
       case Token::PERIOD: {
+        *is_async = false;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
         ArrowFormalParametersUnexpectedToken(classifier);
@@ -2843,6 +3076,7 @@ ParserBase<Traits>::ParseMemberExpressionContinuation(
       }
       case Token::TEMPLATE_SPAN:
       case Token::TEMPLATE_TAIL: {
+        *is_async = false;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
         ArrowFormalParametersUnexpectedToken(classifier);
@@ -3005,17 +3239,17 @@ bool ParserBase<Traits>::IsNextLetKeyword() {
     case Token::LET:  // Yes, you can do let let = ... in sloppy mode
     case Token::YIELD:
     case Token::AWAIT:
+    case Token::ASYNC:
       return true;
     default:
       return false;
   }
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseArrowFunctionLiteral(
-    bool accept_IN, const FormalParametersT& formal_parameters,
+    bool accept_IN, const FormalParametersT& formal_parameters, bool is_async,
     const ExpressionClassifier& formals_classifier, bool* ok) {
   if (peek() == Token::ARROW && scanner_->HasAnyLineTerminatorBeforeNext()) {
     // ASI inserts `;` after arrow parameters if a line terminator is found.
@@ -3032,10 +3266,11 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
   int expected_property_count = -1;
   Scanner::Location super_loc;
 
+  FunctionKind arrow_kind = is_async ? kAsyncArrowFunction : kArrowFunction;
   {
     typename Traits::Type::Factory function_factory(ast_value_factory());
     FunctionState function_state(&function_state_, &scope_,
-                                 formal_parameters.scope, kArrowFunction,
+                                 formal_parameters.scope, arrow_kind,
                                  &function_factory);
 
     function_state.SkipMaterializedLiterals(
@@ -3061,7 +3296,7 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
       } else {
         body = this->ParseEagerFunctionBody(
             this->EmptyIdentifier(), RelocInfo::kNoPosition, formal_parameters,
-            kArrowFunction, FunctionLiteral::kAnonymousExpression, CHECK_OK);
+            arrow_kind, FunctionLiteral::kAnonymousExpression, CHECK_OK);
         materialized_literal_count =
             function_state.materialized_literal_count();
         expected_property_count = function_state.expected_property_count();
@@ -3115,7 +3350,7 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
       materialized_literal_count, expected_property_count, num_parameters,
       FunctionLiteral::kNoDuplicateParameters,
       FunctionLiteral::kAnonymousExpression,
-      FunctionLiteral::kShouldLazyCompile, FunctionKind::kArrowFunction,
+      FunctionLiteral::kShouldLazyCompile, arrow_kind,
       formal_parameters.scope->start_position());
 
   function_literal->set_function_token_position(
@@ -3284,13 +3519,12 @@ void ParserBase<Traits>::CheckDestructuringElement(
 #undef CHECK_OK
 #undef CHECK_OK_CUSTOM
 
-
 template <typename Traits>
 void ParserBase<Traits>::ObjectLiteralChecker::CheckProperty(
-    Token::Value property, PropertyKind type, bool is_static, bool is_generator,
+    Token::Value property, PropertyKind type, MethodKind method_type,
     bool* ok) {
-  DCHECK(!is_static);
+  DCHECK(!IsStaticMethod(method_type));
-  DCHECK(!is_generator || type == kMethodProperty);
+  DCHECK(!IsSpecialMethod(method_type) || type == kMethodProperty);
 
   if (property == Token::SMI || property == Token::NUMBER) return;
 
@@ -3305,26 +3539,28 @@ void ParserBase<Traits>::ObjectLiteralChecker::CheckProperty(
   }
 }
 
-
 template <typename Traits>
 void ParserBase<Traits>::ClassLiteralChecker::CheckProperty(
-    Token::Value property, PropertyKind type, bool is_static, bool is_generator,
+    Token::Value property, PropertyKind type, MethodKind method_type,
     bool* ok) {
   DCHECK(type == kMethodProperty || type == kAccessorProperty);
 
   if (property == Token::SMI || property == Token::NUMBER) return;
 
-  if (is_static) {
+  if (IsStaticMethod(method_type)) {
     if (IsPrototype()) {
       this->parser()->ReportMessage(MessageTemplate::kStaticPrototype);
       *ok = false;
       return;
     }
   } else if (IsConstructor()) {
-    if (is_generator || type == kAccessorProperty) {
+    const bool is_generator = IsGeneratorMethod(method_type);
+    const bool is_async = IsAsyncMethod(method_type);
+    if (is_generator || is_async || type == kAccessorProperty) {
       MessageTemplate::Template msg =
           is_generator ? MessageTemplate::kConstructorIsGenerator
-                       : MessageTemplate::kConstructorIsAccessor;
+                       : is_async ? MessageTemplate::kConstructorIsAsync
+                                  : MessageTemplate::kConstructorIsAccessor;
       this->parser()->ReportMessage(msg);
       *ok = false;
       return;

src/parsing/parser.cc

@@ -330,6 +330,10 @@ bool ParserTraits::IsUndefined(const AstRawString* identifier) const {
   return identifier == parser_->ast_value_factory()->undefined_string();
 }
 
+bool ParserTraits::IsAwait(const AstRawString* identifier) const {
+  return identifier == parser_->ast_value_factory()->await_string();
+}
+
 bool ParserTraits::IsPrototype(const AstRawString* identifier) const {
   return identifier == parser_->ast_value_factory()->prototype_string();
 }
@@ -798,6 +802,7 @@ Parser::Parser(ParseInfo* info)
       FLAG_harmony_restrictive_declarations);
   set_allow_harmony_exponentiation_operator(
       FLAG_harmony_exponentiation_operator);
+  set_allow_harmony_async_await(FLAG_harmony_async_await);
   for (int feature = 0; feature < v8::Isolate::kUseCounterFeatureCount;
        ++feature) {
     use_counts_[feature] = 0;
@@ -1075,6 +1080,13 @@ FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
     bool ok = true;
 
     if (shared_info->is_arrow()) {
+      bool is_async = allow_harmony_async_await() && shared_info->is_async();
+      if (is_async) {
+        DCHECK(!scanner()->HasAnyLineTerminatorAfterNext());
+        Consume(Token::ASYNC);
+        DCHECK(peek_any_identifier() || peek() == Token::LPAREN);
+      }
+
       // TODO(adamk): We should construct this scope from the ScopeInfo.
       Scope* scope =
           NewScope(scope_, FUNCTION_SCOPE, FunctionKind::kArrowFunction);
@@ -1115,8 +1127,8 @@ FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
         checkpoint.Restore(&formals.materialized_literals_count);
         // Pass `accept_IN=true` to ParseArrowFunctionLiteral --- This should
         // not be observable, or else the preparser would have failed.
-        Expression* expression =
+        Expression* expression = ParseArrowFunctionLiteral(
-            ParseArrowFunctionLiteral(true, formals, formals_classifier, &ok);
+            true, formals, is_async, formals_classifier, &ok);
         if (ok) {
           // Scanning must end at the same position that was recorded
           // previously. If not, parsing has been interrupted due to a stack
@@ -1255,8 +1267,8 @@ Statement* Parser::ParseStatementListItem(bool* ok) {
   // StatementListItem:
   //    Statement
   //    Declaration
-
+  const Token::Value peeked = peek();
-  switch (peek()) {
+  switch (peeked) {
     case Token::FUNCTION:
       return ParseHoistableDeclaration(NULL, ok);
     case Token::CLASS:
@@ -1271,6 +1283,13 @@ Statement* Parser::ParseStatementListItem(bool* ok) {
         return ParseVariableStatement(kStatementListItem, NULL, ok);
       }
       break;
+    case Token::ASYNC:
+      if (allow_harmony_async_await() && PeekAhead() == Token::FUNCTION &&
+          !scanner()->HasAnyLineTerminatorAfterNext()) {
+        Consume(Token::ASYNC);
+        return ParseAsyncFunctionDeclaration(NULL, ok);
+      }
+    /* falls through */
     default:
       break;
   }
@@ -1560,7 +1579,10 @@ Statement* Parser::ParseExportDefault(bool* ok) {
             pos, FunctionLiteral::kDeclaration, language_mode(), CHECK_OK);
         result = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
       } else {
-        result = ParseHoistableDeclaration(pos, is_generator, &names, CHECK_OK);
+        result = ParseHoistableDeclaration(
+            pos, is_generator ? ParseFunctionFlags::kIsGenerator
+                              : ParseFunctionFlags::kIsNormal,
+            &names, CHECK_OK);
       }
       break;
     }
@@ -1579,6 +1601,30 @@ Statement* Parser::ParseExportDefault(bool* ok) {
       }
       break;
 
+    case Token::ASYNC:
+      if (allow_harmony_async_await() && PeekAhead() == Token::FUNCTION &&
+          !scanner()->HasAnyLineTerminatorAfterNext()) {
+        Consume(Token::ASYNC);
+        Consume(Token::FUNCTION);
+        int pos = position();
+        if (peek() == Token::LPAREN) {
+          // AsyncFunctionDeclaration[+Default] ::
+          //   async [no LineTerminator here] function ( FormalParameters ) {
+          //      AsyncFunctionBody
+          //   }
+          default_export = ParseFunctionLiteral(
+              default_string, Scanner::Location::invalid(),
+              kSkipFunctionNameCheck, FunctionKind::kAsyncFunction, pos,
+              FunctionLiteral::kDeclaration, language_mode(), CHECK_OK);
+          result = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
+        } else {
+          result = ParseHoistableDeclaration(pos, ParseFunctionFlags::kIsAsync,
+                                             &names, CHECK_OK);
+        }
+        break;
+      }
+    /* falls through */
+
     default: {
       int pos = peek_position();
       ExpressionClassifier classifier(this);
@@ -1703,6 +1749,14 @@ Statement* Parser::ParseExportDeclaration(bool* ok) {
       result = ParseVariableStatement(kStatementListItem, &names, CHECK_OK);
       break;
 
+    case Token::ASYNC:
+      if (allow_harmony_async_await()) {
+        Consume(Token::ASYNC);
+        result = ParseAsyncFunctionDeclaration(&names, CHECK_OK);
+        break;
+      }
+    /* falls through */
+
     default:
       *ok = false;
       ReportUnexpectedToken(scanner()->current_token());
@@ -2062,13 +2116,29 @@ Statement* Parser::ParseHoistableDeclaration(
     ZoneList<const AstRawString*>* names, bool* ok) {
   Expect(Token::FUNCTION, CHECK_OK);
   int pos = position();
-  bool is_generator = Check(Token::MUL);
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsNormal;
-  return ParseHoistableDeclaration(pos, is_generator, names, ok);
+  if (Check(Token::MUL)) {
+    flags |= ParseFunctionFlags::kIsGenerator;
+  }
+  return ParseHoistableDeclaration(pos, flags, names, ok);
 }
 
+Statement* Parser::ParseAsyncFunctionDeclaration(
+    ZoneList<const AstRawString*>* names, bool* ok) {
+  DCHECK_EQ(scanner()->current_token(), Token::ASYNC);
+  int pos = position();
+  if (scanner()->HasAnyLineTerminatorBeforeNext()) {
+    *ok = false;
+    ReportUnexpectedToken(scanner()->current_token());
+    return nullptr;
+  }
+  Expect(Token::FUNCTION, CHECK_OK);
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsAsync;
+  return ParseHoistableDeclaration(pos, flags, names, ok);
+}
 
 Statement* Parser::ParseHoistableDeclaration(
-    int pos, bool is_generator, ZoneList<const AstRawString*>* names,
+    int pos, ParseFunctionFlags flags, ZoneList<const AstRawString*>* names,
     bool* ok) {
   // FunctionDeclaration ::
   //   'function' Identifier '(' FormalParameters ')' '{' FunctionBody '}'
@@ -2076,10 +2146,21 @@ Statement* Parser::ParseHoistableDeclaration(
   //   'function' '*' Identifier '(' FormalParameters ')' '{' FunctionBody '}'
   //
   // 'function' and '*' (if present) have been consumed by the caller.
+  const bool is_generator = flags & ParseFunctionFlags::kIsGenerator;
+  const bool is_async = flags & ParseFunctionFlags::kIsAsync;
+  DCHECK(!is_generator || !is_async);
+
   bool is_strict_reserved = false;
   const AstRawString* name = ParseIdentifierOrStrictReservedWord(
       &is_strict_reserved, CHECK_OK);
 
+  if (V8_UNLIKELY(is_async_function() && this->IsAwait(name))) {
+    ReportMessageAt(scanner()->location(),
+                    MessageTemplate::kAwaitBindingIdentifier);
+    *ok = false;
+    return nullptr;
+  }
+
   FuncNameInferrer::State fni_state(fni_);
   if (fni_ != NULL) fni_->PushEnclosingName(name);
   FunctionLiteral* fun = ParseFunctionLiteral(
@@ -2087,7 +2168,8 @@ Statement* Parser::ParseHoistableDeclaration(
       is_strict_reserved ? kFunctionNameIsStrictReserved
                          : kFunctionNameValidityUnknown,
       is_generator ? FunctionKind::kGeneratorFunction
-                   : FunctionKind::kNormalFunction,
+                   : is_async ? FunctionKind::kAsyncFunction
+                              : FunctionKind::kNormalFunction,
       pos, FunctionLiteral::kDeclaration, language_mode(), CHECK_OK);
 
   // Even if we're not at the top-level of the global or a function
@@ -2400,15 +2482,18 @@ static bool ContainsLabel(ZoneList<const AstRawString*>* labels,
 Statement* Parser::ParseFunctionDeclaration(bool* ok) {
   Consume(Token::FUNCTION);
   int pos = position();
-  bool is_generator = Check(Token::MUL);
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsNormal;
-  if (allow_harmony_restrictive_declarations() && is_generator) {
+  if (Check(Token::MUL)) {
-    ParserTraits::ReportMessageAt(
+    flags |= ParseFunctionFlags::kIsGenerator;
-        scanner()->location(),
+    if (allow_harmony_restrictive_declarations()) {
-        MessageTemplate::kGeneratorInLegacyContext);
+      ParserTraits::ReportMessageAt(scanner()->location(),
-    *ok = false;
+                                    MessageTemplate::kGeneratorInLegacyContext);
-    return nullptr;
+      *ok = false;
+      return nullptr;
+    }
   }
-  return ParseHoistableDeclaration(pos, is_generator, nullptr, CHECK_OK);
+
+  return ParseHoistableDeclaration(pos, flags, nullptr, CHECK_OK);
 }
 
 Statement* Parser::ParseExpressionOrLabelledStatement(
@@ -4051,7 +4136,6 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
     CheckArityRestrictions(arity, kind, formals.has_rest, start_position,
                            formals_end_position, CHECK_OK);
     Expect(Token::LBRACE, CHECK_OK);
-
     // Don't include the rest parameter into the function's formal parameter
     // count (esp. the SharedFunctionInfo::internal_formal_parameter_count,
     // which says whether we need to create an arguments adaptor frame).
@@ -4207,6 +4291,36 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
   return function_literal;
 }
 
+Expression* Parser::ParseAsyncFunctionExpression(bool* ok) {
+  // AsyncFunctionDeclaration ::
+  //   async [no LineTerminator here] function ( FormalParameters[Await] )
+  //       { AsyncFunctionBody }
+  //
+  //   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);
+  bool is_strict_reserved = false;
+  const AstRawString* name = nullptr;
+  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 nullptr;
+    }
+  }
+  return ParseFunctionLiteral(name, scanner()->location(),
+                              is_strict_reserved ? kFunctionNameIsStrictReserved
+                                                 : kFunctionNameValidityUnknown,
+                              FunctionKind::kAsyncFunction, pos, type,
+                              language_mode(), CHECK_OK);
+}
 
 void Parser::SkipLazyFunctionBody(int* materialized_literal_count,
                                   int* expected_property_count, bool* ok,
@@ -4606,6 +4720,7 @@ PreParser::PreParseResult Parser::ParseLazyFunctionBodyWithPreParser(
     SET_ALLOW(harmony_function_sent);
     SET_ALLOW(harmony_exponentiation_operator);
     SET_ALLOW(harmony_restrictive_declarations);
+    SET_ALLOW(harmony_async_await);
 #undef SET_ALLOW
   }
   PreParser::PreParseResult result = reusable_preparser_->PreParseLazyFunction(
@@ -4676,13 +4791,12 @@ ClassLiteral* Parser::ParseClassLiteral(ExpressionClassifier* classifier,
     if (Check(Token::SEMICOLON)) continue;
     FuncNameInferrer::State fni_state(fni_);
     const bool in_class = true;
-    const bool is_static = false;
     bool is_computed_name = false;  // Classes do not care about computed
                                     // property names here.
     ExpressionClassifier property_classifier(this);
     const AstRawString* property_name = nullptr;
     ObjectLiteral::Property* property = ParsePropertyDefinition(
-        &checker, in_class, has_extends, is_static, &is_computed_name,
+        &checker, in_class, has_extends, MethodKind::Normal, &is_computed_name,
         &has_seen_constructor, &property_classifier, &property_name, CHECK_OK);
     RewriteNonPattern(&property_classifier, CHECK_OK);
     if (classifier != nullptr) {
@@ -5313,6 +5427,17 @@ void Parser::MarkCollectedTailCallExpressions() {
   }
 }
 
+Expression* ParserTraits::ExpressionListToExpression(
+    ZoneList<Expression*>* args) {
+  AstNodeFactory* factory = parser_->factory();
+  Expression* expr = args->at(0);
+  for (int i = 1; i < args->length(); ++i) {
+    expr = factory->NewBinaryOperation(Token::COMMA, expr, args->at(i),
+                                       expr->position());
+  }
+  return expr;
+}
+
 void ParserTraits::RewriteDestructuringAssignments() {
   parser_->RewriteDestructuringAssignments();
 }
@@ -5333,6 +5458,11 @@ void ParserTraits::RewriteNonPattern(Type::ExpressionClassifier* classifier,
   parser_->RewriteNonPattern(classifier, ok);
 }
 
+Expression* ParserTraits::RewriteAwaitExpression(Expression* value, int pos) {
+  // TODO(caitp): Implement AsyncFunctionAwait()
+  // per tc39.github.io/ecmascript-asyncawait/#abstract-ops-async-function-await
+  return value;
+}
 
 Zone* ParserTraits::zone() const {
   return parser_->function_state_->scope()->zone();

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);
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsNormal;
-  return ParseHoistableDeclaration(pos, is_generator, CHECK_OK);
+  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);
+  ParseFunctionFlags flags = ParseFunctionFlags::kIsNormal;
-  if (allow_harmony_restrictive_declarations() && is_generator) {
+  if (Check(Token::MUL)) {
-    PreParserTraits::ReportMessageAt(
+    flags |= ParseFunctionFlags::kIsGenerator;
-        scanner()->location(),
+    if (allow_harmony_restrictive_declarations()) {
-        MessageTemplate::kGeneratorInLegacyContext);
+      PreParserTraits::ReportMessageAt(
-    *ok = false;
+          scanner()->location(), MessageTemplate::kGeneratorInLegacyContext);
-    return Statement::Default();
+      *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] = {