[modules] Don't throw when detecting cycle while processing star exports.

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 19689 matching lines @@
 MaybeHandle<Cell> Module::ResolveExport(Handle<Module> module,
                                         Handle<String> name, bool must_resolve,
                                         Module::ResolveSet* resolve_set) {
   Isolate* isolate = module->GetIsolate();
   Handle<Object> object(module->exports()->Lookup(name), isolate);
   if (object->IsCell()) {
     // Already resolved (e.g. because it's a local export).
     return Handle<Cell>::cast(object);
   }
 
-  // Must be an indirect export of some sort, so we need to detect cycles.
+  // Check for cycle before recursing.
   {
     // Attempt insertion with a null string set.
     auto result = resolve_set->insert({module, nullptr});
     UnorderedStringSet*& name_set = result.first->second;
-    bool did_insert = result.second;
-    if (did_insert) {
+    if (result.second) {
       // |module| wasn't in the map previously, so allocate a new name set.
       Zone* zone = resolve_set->zone();
       name_set =
           new (zone->New(sizeof(UnorderedStringSet))) UnorderedStringSet(zone);
     } else if (name_set->count(name)) {
-      // TODO(adamk): Throwing here is incorrect in the case of star exports.
-      THROW_NEW_ERROR(
-          isolate,
-          NewSyntaxError(MessageTemplate::kCyclicModuleDependency, name), Cell);
+      // Cycle detected.
+      if (must_resolve) {
+        THROW_NEW_ERROR(
+            isolate,
+            NewSyntaxError(MessageTemplate::kCyclicModuleDependency, name),
+            Cell);
+      }
+      return MaybeHandle<Cell>();
     }
     name_set->insert(name);
   }
 
   if (object->IsModuleInfoEntry()) {
     // Not yet resolved indirect export.
     Handle<ModuleInfoEntry> entry = Handle<ModuleInfoEntry>::cast(object);
     int module_request = Smi::cast(entry->module_request())->value();
     Handle<String> import_name(String::cast(entry->import_name()), isolate);
 
@@ skipping 159 matching lines @@
             .is_null()) {
       return false;
     }
   }
 
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8