reproduce v8 fast api bug

src/workerd/jsg/BUILD.bazel

@@ -282,6 +282,7 @@ wd_cc_library(
     src = f,
     local_defines = ["JSG_IMPLEMENTATION"],
     deps = [":jsg"],
+    size = "enormous",
 ) for f in glob(
     ["*-test.c++"],
     exclude = [

src/workerd/jsg/fast-api.h

@@ -63,8 +63,7 @@ concept FastApiPrimitive = kj::isSameType<T, void>() || kj::isSameType<T, bool>(
 
 // Helper to determine if a type can be used as a parameter in V8 Fast API
 template <typename T>
-concept FastApiParam = !isFunctionCallbackInfo<kj::RemoveConst<kj::Decay<T>>> &&
-    !isKjPromise<kj::RemoveConst<kj::Decay<T>>> && !isJsgPromise<kj::RemoveConst<kj::Decay<T>>>;
+concept FastApiParam = !isFunctionCallbackInfo<kj::RemoveConst<kj::Decay<T>>>;
 
 // Helper to determine if a type can be used as a return value in a V8 Fast API
 template <typename T>
@@ -106,6 +105,8 @@ struct FastApiJSGToV8 {
   using value = v8::Local<v8::Value>;
 };
 
+// TODO(soon): Address this.
+// Removing v8::FastOneByteString will fix GC related issues.
 template <typename T>
   requires StringLike<kj::RemoveConst<kj::Decay<T>>>
 struct FastApiJSGToV8<T> {

src/workerd/jsg/promise.h

@@ -618,6 +618,7 @@ class PromiseWrapper {
     if (handle->IsPromise()) {
       auto promise = handle.As<v8::Promise>();
       if constexpr (!isVoid<T>() && !isV8Ref<T>()) {
+        js.v8Isolate->RequestGarbageCollectionForTesting(v8::Isolate::kFullGarbageCollection);
         // Add a .then() to unwrap the promise's resolution (i.e. convert it from JS to C++).
         // Note that we don't need to handle the rejection case here as there is no wrapping
         // applied to exception values, so we just let it propagate through.

src/workerd/jsg/value.h

@@ -516,6 +516,8 @@ class StringWrapper {
   template <StringLike T>
   kj::Maybe<T> tryUnwrap(
       Lock& js, v8::Local<v8::Context> context, const v8::FastOneByteString& handle, T*) {
+        KJ_DBG("Converting FAST ONE BYTE STRING");
+    // js.v8Isolate->RequestGarbageCollectionForTesting(v8::Isolate::kFullGarbageCollection);
     size_t utf8_length = simdutf::utf8_length_from_latin1(handle.data, handle.length);
     kj::Array<char> buf = kj::heapArray<char>(utf8_length + 1);
     buf[utf8_length] = '\0';