LibWeb: Make the drag data store reference counted

Ownership of the drag data store is a bit weird. In a normal drag-and-
drop operation, the DragAndDropEventHandler owns the store. When events
are fired for the operation, the DataTransfer object assigned to those
events are "associated" with the store. We currently represent that with
an Optional<DragDataStore&>.

However, it's also possible to create DataTransfer objects from scripts.
Those objects create their own drag data store. This puts DataTransfer
in a weird situation where it may own a store or just reference one.

Rather than coming up with something like Variant<DDS, DDS&> or using
MaybeOwned<DDS> here, we can get by with just making the store reference
counted.

Userland/Libraries/LibWeb/HTML/DataTransfer.cpp

@@ -76,7 +76,7 @@ void DataTransfer::set_effect_allowed(FlyString effect_allowed)
     // On setting, if drag data store's mode is the read/write mode and the new value is one of "none", "copy", "copyLink",
     // "copyMove", "link", "linkMove", "move", "all", or "uninitialized", then the attribute's current value must be set
     // to the new value. Otherwise, it must be left unchanged.
-    if (m_associated_drag_data_store.has_value() && m_associated_drag_data_store->mode() == DragDataStore::Mode::ReadWrite)
+    if (m_associated_drag_data_store && m_associated_drag_data_store->mode() == DragDataStore::Mode::ReadWrite)
         set_effect_allowed_internal(move(effect_allowed));
 }
 
@@ -109,7 +109,7 @@ ReadonlySpan<String> DataTransfer::types() const
 String DataTransfer::get_data(String const& format_argument) const
 {
     // 1. If the DataTransfer object is no longer associated with a drag data store, then return the empty string.
-    if (!m_associated_drag_data_store.has_value())
+    if (!m_associated_drag_data_store)
         return {};
 
     // 2. If the drag data store's mode is the protected mode, then return the empty string.
@@ -165,7 +165,7 @@ JS::NonnullGCPtr<FileAPI::FileList> DataTransfer::files() const
 
     // 2. If the DataTransfer object is no longer associated with a drag data store, the FileList is empty. Return
     //    the empty list L.
-    if (!m_associated_drag_data_store.has_value())
+    if (!m_associated_drag_data_store)
         return files;
 
     // 3. If the drag data store's mode is the protected mode, return the empty list L.
@@ -195,9 +195,9 @@ JS::NonnullGCPtr<FileAPI::FileList> DataTransfer::files() const
     return files;
 }
 
-void DataTransfer::associate_with_drag_data_store(DragDataStore& drag_data_store)
+void DataTransfer::associate_with_drag_data_store(NonnullRefPtr<DragDataStore> drag_data_store)
 {
-    m_associated_drag_data_store = drag_data_store;
+    m_associated_drag_data_store = move(drag_data_store);
     update_data_transfer_types_list();
 }
 
@@ -214,7 +214,7 @@ void DataTransfer::update_data_transfer_types_list()
     Vector<String> types;
 
     // 2. If the DataTransfer object is still associated with a drag data store, then:
-    if (m_associated_drag_data_store.has_value()) {
+    if (m_associated_drag_data_store) {
         bool contains_file = false;
 
         // 1. For each item in the DataTransfer object's drag data store item list whose kind is text, add an entry to L

Userland/Libraries/LibWeb/HTML/DataTransfer.h

@@ -55,7 +55,7 @@ public:
     String get_data(String const& format) const;
     JS::NonnullGCPtr<FileAPI::FileList> files() const;
 
-    void associate_with_drag_data_store(DragDataStore& drag_data_store);
+    void associate_with_drag_data_store(NonnullRefPtr<DragDataStore> drag_data_store);
     void disassociate_with_drag_data_store();
 
 private:
@@ -79,7 +79,7 @@ private:
     Vector<String> m_types;
 
     // https://html.spec.whatwg.org/multipage/dnd.html#the-datatransfer-interface:drag-data-store-3
-    Optional<DragDataStore&> m_associated_drag_data_store;
+    RefPtr<DragDataStore> m_associated_drag_data_store;
 };
 
 }

Userland/Libraries/LibWeb/HTML/DragDataStore.cpp

@@ -9,6 +9,11 @@
 
 namespace Web::HTML {
 
+NonnullRefPtr<DragDataStore> DragDataStore::create()
+{
+    return adopt_ref(*new DragDataStore());
+}
+
 DragDataStore::DragDataStore()
     : m_allowed_effects_state(DataTransferEffect::uninitialized)
 {

Userland/Libraries/LibWeb/HTML/DragDataStore.h

@@ -9,6 +9,8 @@
 #include <AK/ByteBuffer.h>
 #include <AK/ByteString.h>
 #include <AK/FlyString.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
 #include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibGfx/Bitmap.h>
@@ -33,7 +35,7 @@ struct DragDataStoreItem {
 };
 
 // https://html.spec.whatwg.org/multipage/dnd.html#drag-data-store
-class DragDataStore {
+class DragDataStore : public RefCounted<DragDataStore> {
 public:
     enum class Mode {
         ReadWrite,
@@ -41,7 +43,7 @@ public:
         Protected,
     };
 
-    DragDataStore();
+    static NonnullRefPtr<DragDataStore> create();
     ~DragDataStore();
 
     void add_item(DragDataStoreItem item) { m_item_list.append(move(item)); }
@@ -55,6 +57,8 @@ public:
     void set_allowed_effects_state(FlyString allowed_effects_state) { m_allowed_effects_state = move(allowed_effects_state); }
 
 private:
+    DragDataStore();
+
     // https://html.spec.whatwg.org/multipage/dnd.html#drag-data-store-item-list
     Vector<DragDataStoreItem> m_item_list;
 

Userland/Libraries/LibWeb/Page/DragAndDropEventHandler.cpp

@@ -51,7 +51,7 @@ bool DragAndDropEventHandler::handle_drag_start(
 
     // 2. Create a drag data store. All the DND events fired subsequently by the steps in this section must use this drag
     //    data store.
-    m_drag_data_store.emplace();
+    m_drag_data_store = HTML::DragDataStore::create();
 
     // 3. Establish which DOM node is the source node, as follows:
     //
@@ -185,7 +185,7 @@ bool DragAndDropEventHandler::handle_drag_move(
     unsigned buttons,
     unsigned modifiers)
 {
-    if (!m_drag_data_store.has_value())
+    if (!has_ongoing_drag_and_drop_operation())
         return false;
 
     auto fire_a_drag_and_drop_event = [&](JS::GCPtr<DOM::EventTarget> target, FlyString const& name, JS::GCPtr<DOM::EventTarget> related_target = nullptr) {
@@ -361,7 +361,7 @@ bool DragAndDropEventHandler::handle_drag_end(
     unsigned buttons,
     unsigned modifiers)
 {
-    if (!m_drag_data_store.has_value())
+    if (!has_ongoing_drag_and_drop_operation())
         return false;
 
     auto fire_a_drag_and_drop_event = [&](JS::GCPtr<DOM::EventTarget> target, FlyString const& name, JS::GCPtr<DOM::EventTarget> related_target = nullptr) {

Userland/Libraries/LibWeb/Page/DragAndDropEventHandler.h

@@ -18,7 +18,7 @@ class DragAndDropEventHandler {
 public:
     void visit_edges(JS::Cell::Visitor& visitor) const;
 
-    bool has_ongoing_drag_and_drop_operation() const { return m_drag_data_store.has_value(); }
+    bool has_ongoing_drag_and_drop_operation() const { return !m_drag_data_store.is_null(); }
 
     bool handle_drag_start(JS::Realm&, CSSPixelPoint screen_position, CSSPixelPoint page_offset, CSSPixelPoint client_offset, CSSPixelPoint offset, unsigned button, unsigned buttons, unsigned modifiers, Vector<HTML::SelectedFile> files);
     bool handle_drag_move(JS::Realm&, JS::NonnullGCPtr<DOM::Document>, JS::NonnullGCPtr<DOM::Node>, CSSPixelPoint screen_position, CSSPixelPoint page_offset, CSSPixelPoint client_offset, CSSPixelPoint offset, unsigned button, unsigned buttons, unsigned modifiers);
@@ -49,7 +49,7 @@ private:
 
     void reset();
 
-    Optional<HTML::DragDataStore> m_drag_data_store;
+    RefPtr<HTML::DragDataStore> m_drag_data_store;
 
     // https://html.spec.whatwg.org/multipage/dnd.html#source-node
     JS::GCPtr<DOM::EventTarget> m_source_node;