Did you benchmark this? The point of MaybeStackBuffer is to avoid an extra heap allocation, as the name implies, a benefit that gets lost when switching to LocalVector

I think we probably don't have a choice according to https://chromium-review.googlesource.com/c/v8/v8/+/4905902 - the Local handles are not supposed to be heap-allocated in the usual fashion, so a MaybeStackBuffer<Local<>> that heap-allocates (when the size > kStackStorageSize) is invalid in the first place and we were probably just being lucky to dodge some memory failures that could be caused by it (or maybe we'll get hit when V8 enables conservative stack scanning). LocalVector was added as a V8-acknowledged way to properly heap allocate them.

Although, another way to go with this while preserving the stack-allocation part may be to add a different MaybeStackBuffer that uses LocalVector when it goes heap-allocated, or add some specialization to MaybeStackBuffer so that the heap-allocated part uses LocalVector when the element type is Local (seems messier though).

@joyeecheung Yeah, those sound like good ideas for solving this problem to me 🙂

Q: How can we disallow heap allocation on Local handles? What's the best way?

targos@0982497

It breaks the world: https://ci.nodejs.org/view/All/job/node-test-commit-arm-debug/15086/nodes=ubuntu2204_debug-arm64/console

Let's see if it breaks here as well. Thanks for the tip @targos: cloudflare/workerd#2752