API: expose isReadonlySymbol

[ajafff]

Search Terms

readonly symbol property

Suggestion

Expose isReadonlySymbol as a method on TypeChecker.

Currently there's no way to tell for sure if a property is readonly.
While cumbersome userland implementations can check for readonly modifier in Symbol.declarations, if it's a GetAccessor without corresponding SetAccessor or if it originated in Object.definePropery(this, 'propName', {value, writable: false}).

However, there's one more thing: Readonly mapped type only sets Symbol.checkFlags which is internal.

So at the very least I need an API to tell if a property's symbol comes from a mapped type with a readonly modifier.

/cc Christian Schulz (@CSchulz) you probably need the same API for the lint rule you want to develop.

[bradzacher]

I've just run into this as well in building out typescript-eslint/typescript-eslint#514.
Would be great to have isReadonlySymbol exposed from the type checker so we don't have to implement our own logic for it.

[neelance]

This would be useful for us as well.

[dragomirtitian]

I am currently writing a documentation system that relies on type information. I want to show members of object types that went through some mapping process and the ability to know if the resulting property is readonly or not would be really useful.