1848788 - Make [NewObject] no-op and make the current behavior out-out

Status: NEW

(Core :: DOM: Bindings (WebIDL), task)

Description

[Kagami Rosylight [:saschanaz] (they/them)]

Specifications frequently omit [NewObject] because it means nothing to specs. It's confusing that Gecko has build time behavior for NewObject as it's frequently ignored when developers copy-paste the IDL from the spec.

For now what NewObject does in Gecko are:

• Build time error when used together with [DependsOn=Nothing]/[DependsOn=DOMState]/[Cached]/[StoreInSlot]
• Implies either [Throws] or [CanOOM] when returning JS object including Promises
• Prevents raw pointer return type by C++ static assertion

Can we make these behavior by default and provide a way to opt-out by other attributes, so that it can be more straightforward to align Gecko IDL with spec IDLs?