From ae6d105f41f7cb1e7afb1cd41f16788954382980 Mon Sep 17 00:00:00 2001
From: Shannon Booth <shannon@serenityos.org>
Date: Thu, 14 Nov 2024 20:17:33 +1300
Subject: [PATCH] LibJS: Use a Function to indirectly let Heap visit VM's GC
 roots

This allows the heap to mark cells that it needs to mark as roots
without needing to directly reference the VM.
---
 Libraries/LibJS/Heap/Heap.cpp  | 7 ++++---
 Libraries/LibJS/Heap/Heap.h    | 4 +++-
 Libraries/LibJS/Runtime/VM.cpp | 4 +++-
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/Libraries/LibJS/Heap/Heap.cpp b/Libraries/LibJS/Heap/Heap.cpp
index 4406060ba8f..47c92c425b7 100644
--- a/Libraries/LibJS/Heap/Heap.cpp
+++ b/Libraries/LibJS/Heap/Heap.cpp
@@ -7,6 +7,7 @@
 
 #include <AK/Badge.h>
 #include <AK/Debug.h>
+#include <AK/Function.h>
 #include <AK/HashTable.h>
 #include <AK/JsonArray.h>
 #include <AK/JsonObject.h>
@@ -19,7 +20,6 @@
 #include <LibJS/Heap/Heap.h>
 #include <LibJS/Heap/HeapBlock.h>
 #include <LibJS/Heap/NanBoxedValue.h>
-#include <LibJS/Runtime/VM.h>
 #include <setjmp.h>
 
 #ifdef HAS_ADDRESS_SANITIZER
@@ -28,8 +28,9 @@
 
 namespace JS {
 
-Heap::Heap(VM& vm)
+Heap::Heap(VM& vm, Function<void(HashMap<Cell*, JS::HeapRoot>&)> gather_embedder_roots)
     : HeapBase(vm)
+    , m_gather_embedder_roots(move(gather_embedder_roots))
 {
     static_assert(HeapBlock::min_possible_cell_size <= 32, "Heap Cell tracking uses too much data!");
     m_size_based_cell_allocators.append(make<CellAllocator>(64));
@@ -259,7 +260,7 @@ void Heap::collect_garbage(CollectionType collection_type, bool print_report)
 
 void Heap::gather_roots(HashMap<Cell*, HeapRoot>& roots)
 {
-    vm().gather_roots(roots);
+    m_gather_embedder_roots(roots);
     gather_conservative_roots(roots);
 
     for (auto& handle : m_handles)
diff --git a/Libraries/LibJS/Heap/Heap.h b/Libraries/LibJS/Heap/Heap.h
index 5a38dd25f9d..694a70d81a5 100644
--- a/Libraries/LibJS/Heap/Heap.h
+++ b/Libraries/LibJS/Heap/Heap.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Badge.h>
+#include <AK/Function.h>
 #include <AK/HashTable.h>
 #include <AK/IntrusiveList.h>
 #include <AK/Noncopyable.h>
@@ -32,7 +33,7 @@ class Heap : public HeapBase {
     AK_MAKE_NONMOVABLE(Heap);
 
 public:
-    explicit Heap(VM&);
+    explicit Heap(VM&, Function<void(HashMap<Cell*, JS::HeapRoot>&)> gather_embedder_roots);
     ~Heap();
 
     template<typename T, typename... Args>
@@ -145,6 +146,7 @@ private:
 
     bool m_collecting_garbage { false };
     StackInfo m_stack_info;
+    Function<void(HashMap<Cell*, JS::HeapRoot>&)> m_gather_embedder_roots;
 };
 
 inline void Heap::did_create_handle(Badge<HandleImpl>, HandleImpl& impl)
diff --git a/Libraries/LibJS/Runtime/VM.cpp b/Libraries/LibJS/Runtime/VM.cpp
index 111bf8ad760..afc5538bc49 100644
--- a/Libraries/LibJS/Runtime/VM.cpp
+++ b/Libraries/LibJS/Runtime/VM.cpp
@@ -62,7 +62,9 @@ static constexpr auto make_single_ascii_character_strings(IndexSequence<code_poi
 static constexpr auto single_ascii_character_strings = make_single_ascii_character_strings(MakeIndexSequence<128>());
 
 VM::VM(OwnPtr<CustomData> custom_data, ErrorMessages error_messages)
-    : m_heap(*this)
+    : m_heap(*this, [this](HashMap<Cell*, JS::HeapRoot>& roots) {
+        gather_roots(roots);
+    })
     , m_error_messages(move(error_messages))
     , m_custom_data(move(custom_data))
 {