[@ember/routing] private namespacing

Cross post from https://github.com/DefinitelyTyped/DefinitelyTyped/issues/37323

Which package(s) does this problem pertain to?

• @types/ember__routing

What are instructions we can follow to reproduce the issue?

ember new sample; cd ./sample # Create a new ember app
ember install ember-cli-typescript # Set up typescript support

Try to add types for the beforeModel hook in a route with the transition argument

beforeModel(this: EditRoute, transition: Transition)

Observe that the transition types are imported from:

import Transition from '@ember/routing/-private/transition'

Can this be exported in a public space since this is a public API?

[chriskrycho]

Thanks for filing this! Since its existence and methods are public API, I agree that the interface should be importable. We want to make sure that only an interface is importable so that the types represent the design of the actual type, which is that it is not available to import as a class and is therefore not open for arbitrary extension e.g. via sub-classing.

Any objections to exporting under those terms @jamescdavis @dfreeman @mike-north?

[MrChocolatine]

This is sensibly the same thing but check out the documentation: https://docs.ember-cli-typescript.com/ember/routes

Basically, both recommend to reuse what is returned by public methods. That way you can’t be wrong since you get exactly what it is used internally:

import type RouterService from '@ember/routing/router-service';
type Transition = ReturnType<RouterService['transitionTo']>;