From b3bfd02e64b4e5a0754c157b18dd42427c931923 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Wed, 21 Aug 2024 08:57:16 -0400
Subject: [PATCH] LibWeb: Store a list of DataTransferItem on the DataTransfer
 object

When scripts receive a DataTransferItem from any IDL method, the spec
requires we return the same DataTransferItem for a particular item in
the drag data store. Meaning, we cannot just create these on the fly as
needed.

To do this, we store a list of DataTransferItem on the DataTransfer
object. We will return one of these objects any time one is requested by
a script.

It feels a bit weird to have the DataTransfer object store: the drag
data store, a DataTransferItemList, and a list of DataTransferItem. But
this is how other engines implement this as well. It basically has to be
this way as DataTransferItemList is just a proxy to the DataTransfer -
meaning, DataTransfer is the source of truth for all IDL access.
---
 Userland/Libraries/LibWeb/HTML/DataTransfer.cpp | 8 ++++++++
 Userland/Libraries/LibWeb/HTML/DataTransfer.h   | 1 +
 2 files changed, 9 insertions(+)

diff --git a/Userland/Libraries/LibWeb/HTML/DataTransfer.cpp b/Userland/Libraries/LibWeb/HTML/DataTransfer.cpp
index 9686a57674d..930ce99ccd0 100644
--- a/Userland/Libraries/LibWeb/HTML/DataTransfer.cpp
+++ b/Userland/Libraries/LibWeb/HTML/DataTransfer.cpp
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Enumerate.h>
 #include <AK/Find.h>
 #include <LibJS/Runtime/Realm.h>
 #include <LibWeb/Bindings/DataTransferPrototype.h>
@@ -12,6 +13,7 @@
 #include <LibWeb/FileAPI/File.h>
 #include <LibWeb/FileAPI/FileList.h>
 #include <LibWeb/HTML/DataTransfer.h>
+#include <LibWeb/HTML/DataTransferItem.h>
 #include <LibWeb/HTML/DataTransferItemList.h>
 #include <LibWeb/Infra/Strings.h>
 
@@ -51,6 +53,11 @@ DataTransfer::DataTransfer(JS::Realm& realm, NonnullRefPtr<DragDataStore> drag_d
     : PlatformObject(realm)
     , m_associated_drag_data_store(move(drag_data_store))
 {
+    for (auto const& [i, item] : enumerate(m_associated_drag_data_store->item_list())) {
+        auto data_transfer_item = DataTransferItem::create(realm, *this, i);
+        m_item_list.append(data_transfer_item);
+    }
+
     update_data_transfer_types_list();
 }
 
@@ -66,6 +73,7 @@ void DataTransfer::visit_edges(JS::Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
     visitor.visit(m_items);
+    visitor.visit(m_item_list);
 }
 
 void DataTransfer::set_drop_effect(String const& drop_effect)
diff --git a/Userland/Libraries/LibWeb/HTML/DataTransfer.h b/Userland/Libraries/LibWeb/HTML/DataTransfer.h
index eb6941df74d..b4ad54a2f70 100644
--- a/Userland/Libraries/LibWeb/HTML/DataTransfer.h
+++ b/Userland/Libraries/LibWeb/HTML/DataTransfer.h
@@ -74,6 +74,7 @@ private:
 
     // https://html.spec.whatwg.org/multipage/dnd.html#dom-datatransfer-items
     JS::GCPtr<DataTransferItemList> m_items;
+    Vector<JS::NonnullGCPtr<DataTransferItem>> m_item_list;
 
     // https://html.spec.whatwg.org/multipage/dnd.html#concept-datatransfer-types
     Vector<String> m_types;