Ensure scopes are backed by blocks in the body of for loops

src/parser.cc

 // Copyright 2012 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.
 
 #include "src/parser.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/ast-literal-reindexer.h"
 #include "src/bailout-reason.h"
@@ skipping 3768 matching lines @@
             expression, lhs_beg_pos, lhs_end_pos,
             MessageTemplate::kInvalidLhsInFor, kSyntaxError, CHECK_OK);
 
         ForEachStatement* loop =
             factory()->NewForEachStatement(mode, labels, stmt_pos);
         Target target(&this->target_stack_, loop);
 
         Expression* enumerable = ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
 
+        // Make a block around the statement in case a lexical binding
+        // is introduced, e.g. by a FunctionDeclaration.
+        Block* block =
+            factory()->NewBlock(NULL, 1, false, RelocInfo::kNoPosition);
         Statement* body = ParseSubStatement(NULL, CHECK_OK);
-        InitializeForEachStatement(loop, expression, enumerable, body);
+        block->statements()->Add(body, zone());
+        InitializeForEachStatement(loop, expression, enumerable, block);
         scope_ = saved_scope;
         for_scope->set_end_position(scanner()->location().end_pos);
         for_scope = for_scope->FinalizeBlockScope();
-        DCHECK(for_scope == NULL);
+        if (for_scope != nullptr) {
+          block->set_scope(for_scope);
+        }
         // Parsed for-in loop.
         return loop;
 
       } else {
         init = factory()->NewExpressionStatement(expression, lhs_beg_pos);
       }
     }
   }
 
   // Standard 'for' loop
@@ skipping 49 matching lines @@
     if (for_scope) {
       // Rewrite a for statement of the form
       //   for (const x = i; c; n) b
       //
       // into
       //
       //   {
       //     const x = i;
       //     for (; c; n) b
       //   }
-      DCHECK(init != NULL);
+      //
+      // or, desugar
+      //   for (; c; n) b
+      // into
+      //   {
+      //     for (; c; n) b
+      //   }
+      // just in case b introduces a lexical binding some other way, e.g., if b
+      // is a FunctionDeclaration.
       Block* block =
           factory()->NewBlock(NULL, 2, false, RelocInfo::kNoPosition);
-      block->statements()->Add(init, zone());
+      if (init != nullptr) {
+        block->statements()->Add(init, zone());
+      }
       block->statements()->Add(loop, zone());
       block->set_scope(for_scope);
       loop->Initialize(NULL, cond, next, body);
       result = block;
     } else {
       loop->Initialize(init, cond, next, body);
       result = loop;
     }
   }
   return result;
@@ skipping 2441 matching lines @@
 
 Expression* Parser::SpreadCallNew(Expression* function,
                                   ZoneList<v8::internal::Expression*>* args,
                                   int pos) {
   args->InsertAt(0, function, zone());
 
   return factory()->NewCallRuntime(Context::REFLECT_CONSTRUCT_INDEX, args, pos);
 }
 }  // namespace internal
 }  // namespace v8