[modules] Improve error messages.

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 70 matching lines @@
 
 }  // namespace
 
 Handle<ModuleInfoEntry> ModuleDescriptor::Entry::Serialize(
     Isolate* isolate) const {
   CHECK(Smi::IsValid(module_request));  // TODO(neis): Check earlier?
   return ModuleInfoEntry::New(
       isolate, ToStringOrUndefined(isolate, export_name),
       ToStringOrUndefined(isolate, local_name),
       ToStringOrUndefined(isolate, import_name),
-      Handle<Object>(Smi::FromInt(module_request), isolate));
+      Handle<Object>(Smi::FromInt(module_request), isolate), location.beg_pos,
+      location.end_pos);
 }
 
 ModuleDescriptor::Entry* ModuleDescriptor::Entry::Deserialize(
     Isolate* isolate, AstValueFactory* avfactory,
     Handle<ModuleInfoEntry> entry) {
   Entry* result = new (avfactory->zone()) Entry(Scanner::Location::invalid());
   result->export_name = FromStringOrUndefined(
       isolate, avfactory, handle(entry->export_name(), isolate));
   result->local_name = FromStringOrUndefined(
       isolate, avfactory, handle(entry->local_name(), isolate));
@@ skipping 75 matching lines @@
       // Found an indirect export.  Patch export entry and move it from regular
       // to special.
       DCHECK_NULL(entry->import_name);
       DCHECK_LT(entry->module_request, 0);
       DCHECK_NOT_NULL(import->second->import_name);
       DCHECK_LE(0, import->second->module_request);
       DCHECK_LT(import->second->module_request,
                 static_cast<int>(module_requests_.size()));
       entry->import_name = import->second->import_name;
       entry->module_request = import->second->module_request;
+      // Hack: When the indirect export cannot be resolved, we want the error
+      // message to point at the import statement, not at the export statement.
+      // Therefore we overwrite [entry]'s location here.  Note that Validate()
+      // has already checked for duplicate exports, so it's guaranteed that we
+      // won't need to report any error pointing at the (now lost) export
+      // location.
+      entry->location = import->second->location;
       entry->local_name = nullptr;
       AddSpecialExport(entry, zone);
       it = regular_exports_.erase(it);
     } else {
       it++;
     }
   }
 }
 
 namespace {
@@ skipping 60 matching lines @@
       return false;
     }
   }
 
   MakeIndirectExportsExplicit(zone);
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8