Fixup gc visitation in streams readers and writers

Author: jasnell

src/workerd/api/streams/internal.c++

@@ -1838,7 +1838,7 @@ void WritableStreamInternalController::visitForGc(jsg::GcVisitor& visitor) {
   for (auto& event : queue) {
     KJ_SWITCH_ONEOF(event.event) {
       KJ_CASE_ONEOF(write, Write) {
-        visitor.visit(write.promise, write.ref);
+        visitor.visit(write.promise);
       }
       KJ_CASE_ONEOF(close, Close) {
         visitor.visit(close.promise);

src/workerd/api/streams/internal.h

@@ -283,7 +283,6 @@ class WritableStreamInternalController: public WritableStreamController {
     kj::Maybe<jsg::Promise<void>::Resolver> promise;
     std::shared_ptr<v8::BackingStore> ownBytes;
     kj::ArrayPtr<const kj::byte> bytes;
-    kj::Maybe<jsg::Ref<WritableStream>> ref;
   };
   struct Close {
     kj::Maybe<jsg::Promise<void>::Resolver> promise;

src/workerd/api/streams/readable.c++

@@ -155,7 +155,14 @@ void ReaderImpl::releaseLock(jsg::Lock& js) {
 }
 
 void ReaderImpl::visitForGc(jsg::GcVisitor& visitor) {
-  visitor.visit(closedPromise);
+  KJ_IF_SOME(readable, state.tryGet<Attached>()) {
+    visitor.visit(readable);
+  } else {
+    // If the reader is attached, then visiting the readable should visit the
+    // closedPromise via visiting the associated resolver.
+    // Otherwise, we need to visit it directly if they are set.
+    visitor.visit(closedPromise);
+  }
 }
 
 // ======================================================================================

src/workerd/api/streams/writable.c++

@@ -197,7 +197,14 @@ bool WritableStream::inspectExpectsBytes() {
 }
 
 void WritableStreamDefaultWriter::visitForGc(jsg::GcVisitor& visitor) {
-  visitor.visit(closedPromise, readyPromise);
+  KJ_IF_SOME(writable, state.tryGet<Attached>()) {
+    visitor.visit(writable);
+  } else {
+    // If the writer is attached, then visiting the writable should visit the
+    // closedPromise and readyPromise via visiting their associated resolvers.
+    // Otherwise, we need to visit those directly if they are set.
+    visitor.visit(closedPromise, readyPromise);
+  }
 }
 
 // ======================================================================================