WindowServer: Don't start a drag and drop unless holding Primary mouse

Adds a member to record the last processed mouse buttons. If they
do not include MouseButton::Primary, return early before creating
a new drag and drop client. This fixes race conditions in which
MouseUp events canceling or completing a drop could be swallowed
by Overlay creation or postponed by an executing DragOperation,
leaving the operation in limbo.

4 files changed, 6 insertions, 2 deletions

diff --git a/Userland/Services/WindowServer/ConnectionFromClient.cpp b/Userland/Services/WindowServer/ConnectionFromClient.cpp
index 4a547f9df5..04a03cc8c3 100644
--- a/Userland/Services/WindowServer/ConnectionFromClient.cpp
+++ b/Userland/Services/WindowServer/ConnectionFromClient.cpp
@@ -817,7 +817,7 @@ void ConnectionFromClient::start_window_resize(i32 window_id)
 Messages::WindowServer::StartDragResponse ConnectionFromClient::start_drag(String const& text, HashMap<String, ByteBuffer> const& mime_data, Gfx::ShareableBitmap const& drag_bitmap)
 {
     auto& wm = WindowManager::the();
-    if (wm.dnd_client())
+    if (wm.dnd_client() || !(wm.last_processed_buttons() & MouseButton::Primary))
         return false;
 
     wm.start_dnd_drag(*this, text, drag_bitmap.bitmap(), Core::MimeData::construct(mime_data));
diff --git a/Userland/Services/WindowServer/Event.h b/Userland/Services/WindowServer/Event.h
index 6ab2bc59b4..f3fb5ebab1 100644
--- a/Userland/Services/WindowServer/Event.h
+++ b/Userland/Services/WindowServer/Event.h
@@ -48,7 +48,7 @@ public:
     bool is_key_event() const { return type() == KeyUp || type() == KeyDown; }
 };
 
-enum class MouseButton : u8 {
+enum MouseButton : u8 {
     None = 0,
     Primary = 1,
     Secondary = 2,
diff --git a/Userland/Services/WindowServer/WindowManager.cpp b/Userland/Services/WindowServer/WindowManager.cpp
index 0d46f9a98e..f3359c8b27 100644
--- a/Userland/Services/WindowServer/WindowManager.cpp
+++ b/Userland/Services/WindowServer/WindowManager.cpp
@@ -1459,6 +1459,7 @@ void WindowManager::event(Core::Event& event)
             m_previous_event_was_super_keydown = false;
 
         process_mouse_event(mouse_event);
+        m_last_processed_buttons = mouse_event.buttons();
         // TODO: handle transitioning between two stacks
         set_hovered_window(current_window_stack().window_at(mouse_event.position(), WindowStack::IncludeWindowFrame::No));
         return;
diff --git a/Userland/Services/WindowServer/WindowManager.h b/Userland/Services/WindowServer/WindowManager.h
index 3a5459c911..2d69e85fca 100644
--- a/Userland/Services/WindowServer/WindowManager.h
+++ b/Userland/Services/WindowServer/WindowManager.h
@@ -347,6 +347,8 @@ public:
     Window const* automatic_cursor_tracking_window() const { return m_automatic_cursor_tracking_window; }
     void set_automatic_cursor_tracking_window(Window* window) { m_automatic_cursor_tracking_window = window; }
 
+    u8 last_processed_buttons() { return m_last_processed_buttons; }
+
 private:
     explicit WindowManager(Gfx::PaletteImpl const&);
 
@@ -469,6 +471,7 @@ private:
     ResizeDirection m_resize_direction { ResizeDirection::None };
 
     u8 m_keyboard_modifiers { 0 };
+    u8 m_last_processed_buttons { MouseButton::None };
 
     NonnullRefPtr<WindowSwitcher> m_switcher;
     NonnullRefPtr<KeymapSwitcher> m_keymap_switcher;