Feature request: Opaque/nominal types

The problem

It often happens that library functions return objects the type of which is an implementation detail. For example an identifier may be an integer but could suddenly be changed to a string, and the client code shouldn't fail because of that.

Safely typing such an identifier in LLS is currently impossible:

• typing it as integer depends on a potentially unstable implementation detail
• typing it as any is unsound

In other words, structural typing fails when the structure isn't stable or known.

Feature request

An annotations that declares a completely opaque/nominal type. It could be --@opaque typename, --@alias typename without any arguments, or anything else. Values belonging of such a type cannot be inspected in any way and can only be passed around. Values of different opaque types cannot be mixed up (so this is stronger than unknown in typescript)

No se nombran archivos, pruebas ni puntos de entrada. Empieza por localizar el código de anotaciones y comprobación de tipos para alias y tipos desconocidos, y luego sigue cómo se inspeccionan o mezclan los valores. Se considera terminado cuando el language server admite tipos opacos distintos que solo se pueden pasar de un sitio a otro, con cobertura para el comportamiento solicitado.