Revert of [modules] Make duplicate export error deterministic.

src/ast/modules.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/ast/modules.h"
 #include "src/ast/ast-value-factory.h"
 #include "src/ast/scopes.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 118 matching lines @@
       special_exports_.Add(entry, zone);
       it = regular_exports_.erase(it);
     } else {
       it++;
     }
   }
 }
 
 const ModuleDescriptor::Entry* ModuleDescriptor::FindDuplicateExport(
     Zone* zone) const {
-  const ModuleDescriptor::Entry* candidate = nullptr;
   ZoneSet<const AstRawString*> export_names(zone);
   for (const auto& it : regular_exports_) {
     const Entry* entry = it.second;
     DCHECK_NOT_NULL(entry->export_name);
-    DCHECK(entry->location.IsValid());
-    bool is_duplicate = !export_names.insert(entry->export_name).second;
-    if (is_duplicate &&
-        (candidate == nullptr ||
-         entry->location.beg_pos > candidate->location.beg_pos)) {
-      candidate = entry;
-    }
+    if (!export_names.insert(entry->export_name).second) return entry;
   }
   for (auto entry : special_exports_) {
     if (entry->export_name == nullptr) continue;  // Star export.
-    DCHECK(entry->location.IsValid());
-    bool is_duplicate = !export_names.insert(entry->export_name).second;
-    if (is_duplicate &&
-        (candidate == nullptr ||
-         entry->location.beg_pos > candidate->location.beg_pos)) {
-      candidate = entry;
-    }
+    if (!export_names.insert(entry->export_name).second) return entry;
   }
-  return candidate;
+  return nullptr;
 }
 
 bool ModuleDescriptor::Validate(ModuleScope* module_scope,
                                 PendingCompilationErrorHandler* error_handler,
                                 Zone* zone) {
   DCHECK_EQ(this, module_scope->module());
   DCHECK_NOT_NULL(error_handler);
 
   // Report error iff there are duplicate exports.
   {
@@ skipping 17 matching lines @@
       return false;
     }
   }
 
   MakeIndirectExportsExplicit(zone);
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8