Are descriptor structs allowed in ToJSValue?

[eqrion]

One goal I've heard is that descriptor structs can be eventually implemented directly using the existing Shape/Map/Structure objects that Web VMs already use on wasm GC objects.

However, a Shape (in SM at least) is not a JS object and should not be accessible to JS scripts. I don't think it could conceivably work even as an opaque thing like wasm GC objects are now. Things like typeof wouldn't know what to do with it.

[jakobkummerow]

FWIW, while I agree that that's a goal I've heard, the fact that (IIUC) descriptor structs can be passed to JS is the primary reason why I don't think we'll merge descriptor structs into the internal Shape/Map in V8: I don't want to expose our Shapes to JS either.

(Wouldn't be the first nor likely the last time that spec authors have some optimization in mind that implementations aren't actually interested in.)

[tlively]

My intuition is that being able to pass descriptors to JS is more important than the hypothetical optimization of making the descriptor and the Shape/Map the same object. Let's move ahead with that understanding for now, but leave this open until we have performance data confirming that implementing the descriptors and Shapes/Maps as separate objects has acceptable performance.