[modules] Treat top-level functions as lexical

src/parsing/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/parsing/parser.h"
 
 #include "src/api.h"
 #include "src/ast/ast.h"
 #include "src/ast/ast-expression-rewriter.h"
 #include "src/ast/ast-expression-visitor.h"
@@ skipping 2074 matching lines @@
                          : kFunctionNameValidityUnknown,
       is_generator ? FunctionKind::kGeneratorFunction
                    : FunctionKind::kNormalFunction,
       pos, FunctionLiteral::kDeclaration, language_mode(), CHECK_OK);
 
   // Even if we're not at the top-level of the global or a function
   // scope, we treat it as such and introduce the function with its
   // initial value upon entering the corresponding scope.
   // In ES6, a function behaves as a lexical binding, except in
   // a script scope, or the initial scope of eval or another function.
-  VariableMode mode = !scope_->is_declaration_scope() ? LET : VAR;
+  VariableMode mode =
+      (!scope_->is_declaration_scope() || scope_->is_module_scope()) ? LET
+                                                                     : VAR;
   VariableProxy* proxy = NewUnresolved(name, mode);
   Declaration* declaration =
       factory()->NewFunctionDeclaration(proxy, mode, fun, scope_, pos);
   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()) {
     SloppyBlockFunctionStatement* delegate =
         factory()->NewSloppyBlockFunctionStatement(empty, scope_);
     scope_->DeclarationScope()->sloppy_block_function_map()->Declare(name,
@@ skipping 4681 matching lines @@
                         try_block, target);
     final_loop = target;
   }
 
   return final_loop;
 }
 
 
 }  // namespace internal
 }  // namespace v8