From 15629e8925e91ed9dd768d74d964bcda26c20de1 Mon Sep 17 00:00:00 2001
From: Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
Date: Wed, 27 Sep 2023 14:58:14 +0200
Subject: [PATCH] LibWeb: Do not use JS::Handle for mutation observers

Using JS::Handle in WebEngineCustomData means that mutation observers
will live as long as VM while actually they should be deallocated as
soon as they are no longer used in a script that created them.
---
 Userland/Libraries/LibWeb/Bindings/MainThreadVM.h  | 2 +-
 Userland/Libraries/LibWeb/DOM/MutationObserver.cpp | 8 +++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibWeb/Bindings/MainThreadVM.h b/Userland/Libraries/LibWeb/Bindings/MainThreadVM.h
index e3605f8f907..fb5d4cd877e 100644
--- a/Userland/Libraries/LibWeb/Bindings/MainThreadVM.h
+++ b/Userland/Libraries/LibWeb/Bindings/MainThreadVM.h
@@ -49,7 +49,7 @@ struct WebEngineCustomData final : public JS::VM::CustomData {
 
     // https://dom.spec.whatwg.org/#mutation-observer-list
     // FIXME: This should be a set.
-    Vector<JS::Handle<DOM::MutationObserver>> mutation_observers;
+    Vector<JS::NonnullGCPtr<DOM::MutationObserver>> mutation_observers;
 
     JS::Handle<JS::Realm> internal_realm;
 
diff --git a/Userland/Libraries/LibWeb/DOM/MutationObserver.cpp b/Userland/Libraries/LibWeb/DOM/MutationObserver.cpp
index 8c42f3fb2d1..77818ddd419 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationObserver.cpp
+++ b/Userland/Libraries/LibWeb/DOM/MutationObserver.cpp
@@ -29,7 +29,13 @@ MutationObserver::MutationObserver(JS::Realm& realm, JS::GCPtr<WebIDL::CallbackT
     agent_custom_data->mutation_observers.append(*this);
 }
 
-MutationObserver::~MutationObserver() = default;
+MutationObserver::~MutationObserver()
+{
+    auto* agent_custom_data = verify_cast<Bindings::WebEngineCustomData>(vm().custom_data());
+    agent_custom_data->mutation_observers.remove_all_matching([this](auto& observer) {
+        return observer.ptr() == this;
+    });
+}
 
 void MutationObserver::initialize(JS::Realm& realm)
 {