Improve strictness of Annex B 3.3 for generators and async functions

Annex B 3.3 applies only for ordinary FunctionDeclarations, not
GeneratorDeclarations or AsyncFunctionDeclarations. This patch
- Skips applying Annex B 3.3 to async functions
- Adds a flag to refrain from applying it to generators
- UseCounter for how often duplicate function in block occurs
  with generators (unclear how to measure need for hoisting from block)

BUG=v8:4806

Review-Url: https://codereview.chromium.org/1995863002
Cr-Commit-Position: refs/heads/master@{#36557}

src/bootstrapper.cc

@@ -2529,6 +2529,7 @@ EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_string_padding)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(icu_case_mapping)
 #endif
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_async_await)
+EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_restrictive_generators)
 
 void InstallPublicSymbol(Factory* factory, Handle<Context> native_context,
                          const char* name, Handle<Symbol> value) {
@@ -3122,6 +3123,7 @@ bool Genesis::InstallExperimentalNatives() {
 #endif
   static const char* harmony_async_await_natives[] = {
       "native harmony-async-await.js", nullptr};
+  static const char* harmony_restrictive_generators_natives[] = {nullptr};
 
   for (int i = ExperimentalNatives::GetDebuggerCount();
        i < ExperimentalNatives::GetBuiltinsCount(); i++) {

src/flag-definitions.h

@@ -202,6 +202,8 @@ DEFINE_IMPLICATION(es_staging, move_object_start)
   V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")             \
   V(harmony_simd, "harmony simd")                                       \
   V(harmony_do_expressions, "harmony do-expressions")                   \
+  V(harmony_restrictive_generators,                                     \
+    "harmony restrictions on generator declarations")                   \
   V(harmony_regexp_property, "harmony unicode regexp property classes") \
   V(harmony_async_await, "harmony async-await")
 

src/parsing/parser-base.h

@@ -198,7 +198,8 @@ class ParserBase : public Traits {
         allow_harmony_for_in_(false),
         allow_harmony_function_name_(false),
         allow_harmony_function_sent_(false),
-        allow_harmony_async_await_(false) {}
+        allow_harmony_async_await_(false),
+        allow_harmony_restrictive_generators_(false) {}
 
 #define ALLOW_ACCESSORS(name)                           \
   bool allow_##name() const { return allow_##name##_; } \
@@ -219,6 +220,7 @@ class ParserBase : public Traits {
   ALLOW_ACCESSORS(harmony_function_name);
   ALLOW_ACCESSORS(harmony_function_sent);
   ALLOW_ACCESSORS(harmony_async_await);
+  ALLOW_ACCESSORS(harmony_restrictive_generators);
   SCANNER_ACCESSORS(harmony_exponentiation_operator);
 
 #undef SCANNER_ACCESSORS
@@ -1176,6 +1178,7 @@ class ParserBase : public Traits {
   bool allow_harmony_function_name_;
   bool allow_harmony_function_sent_;
   bool allow_harmony_async_await_;
+  bool allow_harmony_restrictive_generators_;
 };
 
 template <class Traits>

src/parsing/parser.cc

@@ -803,6 +803,7 @@ Parser::Parser(ParseInfo* info)
   set_allow_harmony_exponentiation_operator(
       FLAG_harmony_exponentiation_operator);
   set_allow_harmony_async_await(FLAG_harmony_async_await);
+  set_allow_harmony_restrictive_generators(FLAG_harmony_restrictive_generators);
   for (int feature = 0; feature < v8::Isolate::kUseCounterFeatureCount;
        ++feature) {
     use_counts_[feature] = 0;
@@ -1971,10 +1972,24 @@ Variable* Parser::Declare(Declaration* declaration,
     } else if (IsLexicalVariableMode(mode) ||
                IsLexicalVariableMode(var->mode())) {
       // Allow duplicate function decls for web compat, see bug 4693.
+      bool duplicate_allowed = false;
       if (is_sloppy(language_mode()) && is_function_declaration &&
           var->is_function()) {
         DCHECK(IsLexicalVariableMode(mode) &&
                IsLexicalVariableMode(var->mode()));
+        // If the duplication is allowed, then the var will show up
+        // in the SloppyBlockFunctionMap and the new FunctionKind
+        // will be a permitted duplicate.
+        FunctionKind function_kind =
+            declaration->AsFunctionDeclaration()->fun()->kind();
+        duplicate_allowed =
+            scope->DeclarationScope()->sloppy_block_function_map()->Lookup(
+                const_cast<AstRawString*>(name), name->hash()) != nullptr &&
+            !IsAsyncFunction(function_kind) &&
+            !(allow_harmony_restrictive_generators() &&
+              IsGeneratorFunction(function_kind));
+      }
+      if (duplicate_allowed) {
         ++use_counts_[v8::Isolate::kSloppyModeBlockScopedFunctionRedefinition];
       } else {
         // The name was declared in this scope before; check for conflicting
@@ -2188,7 +2203,13 @@ Statement* Parser::ParseHoistableDeclaration(
   Declare(declaration, DeclarationDescriptor::NORMAL, true, CHECK_OK);
   if (names) names->Add(name, zone());
   EmptyStatement* empty = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
-  if (is_sloppy(language_mode()) && !scope_->is_declaration_scope()) {
+  // Async functions don't undergo sloppy mode block scoped hoisting, and don't
+  // allow duplicates in a block. Both are represented by the
+  // sloppy_block_function_map. Don't add them to the map for async functions.
+  // Generators are also supposed to be prohibited; currently doing this behind
+  // a flag and UseCounting violations to assess web compatibility.
+  if (is_sloppy(language_mode()) && !scope_->is_declaration_scope() &&
+      !is_async && !(allow_harmony_restrictive_generators() && is_generator)) {
     SloppyBlockFunctionStatement* delegate =
         factory()->NewSloppyBlockFunctionStatement(empty, scope_);
     scope_->DeclarationScope()->sloppy_block_function_map()->Declare(name,

test/cctest/test-parsing.cc

@@ -1509,7 +1509,8 @@ enum ParserFlag {
   kAllowHarmonyRestrictiveDeclarations,
   kAllowHarmonyExponentiationOperator,
   kAllowHarmonyForIn,
-  kAllowHarmonyAsyncAwait
+  kAllowHarmonyAsyncAwait,
+  kAllowHarmonyRestrictiveGenerators,
 };
 
 enum ParserSyncTestResult {
@@ -1532,6 +1533,8 @@ void SetParserFlags(i::ParserBase<Traits>* parser,
   parser->set_allow_harmony_for_in(flags.Contains(kAllowHarmonyForIn));
   parser->set_allow_harmony_async_await(
       flags.Contains(kAllowHarmonyAsyncAwait));
+  parser->set_allow_harmony_restrictive_generators(
+      flags.Contains(kAllowHarmonyRestrictiveGenerators));
 }
 
 
@@ -7731,3 +7734,60 @@ TEST(RestrictiveForInErrors) {
   RunParserSyncTest(context_data, error_data, kError, nullptr, 0, always_flags,
                     arraysize(always_flags));
 }
+
+TEST(NoDuplicateGeneratorsInBlock) {
+  const char* block_context_data[][2] = {
+      {"'use strict'; {", "}"},
+      {"{", "}"},
+      {"(function() { {", "} })()"},
+      {"(function() {'use strict'; {", "} })()"},
+      {NULL, NULL}};
+  const char* top_level_context_data[][2] = {
+      {"'use strict';", ""},
+      {"", ""},
+      {"(function() {", "})()"},
+      {"(function() {'use strict';", "})()"},
+      {NULL, NULL}};
+  const char* error_data[] = {"function* x() {} function* x() {}",
+                              "function x() {} function* x() {}",
+                              "function* x() {} function x() {}", NULL};
+  static const ParserFlag always_flags[] = {kAllowHarmonyRestrictiveGenerators};
+  // The preparser doesn't enforce the restriction, so turn it off.
+  bool test_preparser = false;
+  RunParserSyncTest(block_context_data, error_data, kError, NULL, 0,
+                    always_flags, arraysize(always_flags), NULL, 0, false,
+                    test_preparser);
+  RunParserSyncTest(top_level_context_data, error_data, kSuccess, NULL, 0,
+                    always_flags, arraysize(always_flags));
+}
+
+TEST(NoDuplicateAsyncFunctionInBlock) {
+  const char* block_context_data[][2] = {
+      {"'use strict'; {", "}"},
+      {"{", "}"},
+      {"(function() { {", "} })()"},
+      {"(function() {'use strict'; {", "} })()"},
+      {NULL, NULL}};
+  const char* top_level_context_data[][2] = {
+      {"'use strict';", ""},
+      {"", ""},
+      {"(function() {", "})()"},
+      {"(function() {'use strict';", "})()"},
+      {NULL, NULL}};
+  const char* error_data[] = {"async function x() {} async function x() {}",
+                              "function x() {} async function x() {}",
+                              "async function x() {} function x() {}",
+                              "function* x() {} async function x() {}",
+                              "function* x() {} async function x() {}",
+                              "async function x() {} function* x() {}",
+                              "function* x() {} async function x() {}",
+                              NULL};
+  static const ParserFlag always_flags[] = {kAllowHarmonyAsyncAwait};
+  // The preparser doesn't enforce the restriction, so turn it off.
+  bool test_preparser = false;
+  RunParserSyncTest(block_context_data, error_data, kError, NULL, 0,
+                    always_flags, arraysize(always_flags), NULL, 0, false,
+                    test_preparser);
+  RunParserSyncTest(top_level_context_data, error_data, kSuccess, NULL, 0,
+                    always_flags, arraysize(always_flags));
+}

test/mjsunit/harmony/sloppy-legacy-duplicate-generators.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --no-harmony-restrictive-generators
+
+// In legacy mode, generators get sloppy-mode block-scoped function hoisting
+
+// Hoisting to the global scope
+
+{
+  function* foo() {}
+  assertEquals('function', typeof foo);
+}
+//assertEquals('function', typeof foo);
+
+// Hoisting within a function scope
+(function() {
+  { function* bar() {} }
+  assertEquals('function', typeof bar);
+})();
+
+// Lexical shadowing allowed; hoisting happens
+(function() {
+  function* x() { yield 1; }
+  { function* x() { yield 2 } }
+  assertEquals(2, x().next().value);
+})();
+
+// Duplicates allowed
+(function() {
+  function* y() { yield 1; }
+  function* y() { yield 2 }
+  assertEquals(2, y().next().value);
+})();
+
+// Functions and generators may duplicate each other
+(function() {
+  function* z() { yield 1; }
+  function z() { return 2 }
+  assertEquals(2, z());
+
+  function a() { return 1; }
+  function* a() { yield 2 }
+  assertEquals(2, a().next().value);
+})();
+
+// In strict mode, none of this happens
+
+(function() {
+  'use strict';
+
+  { function* bar() {} }
+  assertEquals('undefined', typeof bar);
+
+  // Lexical shadowing allowed; hoisting happens
+  function* x() { yield 1; }
+  { function* x() { yield 2 } }
+  assertEquals(1, x().next().value);
+})();

test/mjsunit/harmony/sloppy-no-duplicate-async.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-async-await
+
+// Async functions don't get sloppy-mode block-scoped function hoisting
+
+// No hoisting to the global scope
+
+{
+  async function foo() {}
+  assertEquals('function', typeof foo);
+}
+assertEquals('undefined', typeof foo);
+
+// No hoisting within a function scope
+(function() {
+  { async function bar() {} }
+  assertEquals('undefined', typeof bar);
+})();
+
+// Lexical shadowing allowed, no hoisting
+(function() {
+  var y;
+  async function x() { y = 1; }
+  { async function x() { y = 2; } }
+  x();
+  assertEquals(1, y);
+})();

test/mjsunit/harmony/sloppy-no-duplicate-generators.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-restrictive-generators
+
+// Generators don't get sloppy-mode block-scoped function hoisting
+
+// No hoisting to the global scope
+
+{
+  function* foo() {}
+  assertEquals('function', typeof foo);
+}
+assertEquals('undefined', typeof foo);
+
+// No hoisting within a function scope
+(function() {
+  { function* bar() {} }
+  assertEquals('undefined', typeof bar);
+})();
+
+// Lexical shadowing allowed, no hoisting
+(function() {
+  function* x() { yield 1; }
+  { function* x() { yield 2 } }
+  assertEquals(1, x().next().value);
+})();