[es6] parse arrow ConciseBody with accept_IN flag

Fixes corner case where arrow function ConciseBody expression does not
accept 'in' in productions.

BUG=v8:4472
LOG=N
R=wingo@igalia.com, adamk@chromium.org, rossberg@chromium.org

Review URL: https://codereview.chromium.org/1407633002

Cr-Commit-Position: refs/heads/master@{#31271}

src/parser.cc

@@ -1217,8 +1217,10 @@ FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
 
       if (ok) {
         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 =
-            ParseArrowFunctionLiteral(formals, formals_classifier, &ok);
+            ParseArrowFunctionLiteral(true, formals, 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

src/preparser.h

@@ -714,9 +714,10 @@ class ParserBase : public Traits {
   ExpressionT ParseMemberExpression(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseMemberExpressionContinuation(
       ExpressionT expression, ExpressionClassifier* classifier, bool* ok);
-  ExpressionT ParseArrowFunctionLiteral(
-      const FormalParametersT& parameters,
-      const ExpressionClassifier& classifier, bool* ok);
+  ExpressionT ParseArrowFunctionLiteral(bool accept_IN,
+                                        const FormalParametersT& parameters,
+                                        const ExpressionClassifier& classifier,
+                                        bool* ok);
   ExpressionT ParseTemplateLiteral(ExpressionT tag, int start,
                                    ExpressionClassifier* classifier, bool* ok);
   void AddTemplateExpression(ExpressionT);
@@ -2946,7 +2947,7 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
           duplicate_loc);
     }
     expression = this->ParseArrowFunctionLiteral(
-        parameters, arrow_formals_classifier, CHECK_OK);
+        accept_IN, parameters, arrow_formals_classifier, CHECK_OK);
     return expression;
   }
 
@@ -3882,7 +3883,7 @@ bool ParserBase<Traits>::IsNextLetKeyword() {
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseArrowFunctionLiteral(
-    const FormalParametersT& formal_parameters,
+    bool accept_IN, const FormalParametersT& formal_parameters,
     const ExpressionClassifier& formals_classifier, bool* ok) {
   if (peek() == Token::ARROW && scanner_->HasAnyLineTerminatorBeforeNext()) {
     // ASI inserts `;` after arrow parameters if a line terminator is found.
@@ -3940,7 +3941,7 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
       parenthesized_function_ = false;
       ExpressionClassifier classifier;
       ExpressionT expression =
-          ParseAssignmentExpression(true, &classifier, CHECK_OK);
+          ParseAssignmentExpression(accept_IN, &classifier, CHECK_OK);
       ValidateExpression(&classifier, CHECK_OK);
       body = this->NewStatementList(1, zone());
       this->AddParameterInitializationBlock(formal_parameters, body, CHECK_OK);

test/cctest/test-parsing.cc

@@ -3727,6 +3727,14 @@ TEST(ErrorsArrowFunctions) {
   static const ParserFlag flags[] = {kAllowLazy};
   RunParserSyncTest(context_data, statement_data, kError, flags,
                     arraysize(flags));
+
+  // In a context where a concise arrow body is parsed with [~In] variant,
+  // ensure that an error is reported in both full parser and preparser.
+  const char* loop_context_data[][2] = {{"for (", "; 0;);"},
+                                        {nullptr, nullptr}};
+  const char* loop_expr_data[] = {"f => 'key' in {}", nullptr};
+  RunParserSyncTest(loop_context_data, loop_expr_data, kError, flags,
+                    arraysize(flags));
 }
 
 
@@ -3801,6 +3809,15 @@ TEST(NoErrorsArrowFunctions) {
                                             kAllowHarmonyDestructuring};
   RunParserSyncTest(context_data, statement_data, kSuccess, NULL, 0,
                     always_flags, arraysize(always_flags));
+
+  static const ParserFlag flags[] = {kAllowLazy};
+  // In a context where a concise arrow body is parsed with [~In] variant,
+  // ensure that nested expressions can still use the 'in' operator,
+  const char* loop_context_data[][2] = {{"for (", "; 0;);"},
+                                        {nullptr, nullptr}};
+  const char* loop_expr_data[] = {"f => ('key' in {})", nullptr};
+  RunParserSyncTest(loop_context_data, loop_expr_data, kSuccess, flags,
+                    arraysize(flags));
 }