revisit --noUnusedLocals with "export types can't be named"

[unional]

TypeScript Version:
2.1.5 and nightly (2.2.0-dev.20170125)

Code

// actions.ts
export interface FluxStandardAction<Payload, Meta> {
  type: string,
  payload: Payload,
  meta: Meta
}

export function createActionCreator<Payload, Meta>(type: string)
  : (payload?: Payload, meta?: Meta) => FluxStandardAction<Payload, Meta> {
  return (payload: Payload, meta: any) => {
    return createAction(type, payload, meta)
  }
}

export function createAction<Payload, Meta>(type: string, payload?: Payload, meta?: Meta)
  : FluxStandardAction<Payload, Meta> {
  return { type, payload, meta }
}

// consume.ts
import { FluxStandardAction, createActionCreator } from './actions'

interface AuthenticatePayload {
  authenticating: boolean
  authenticated: boolean,
  username?: string,
  errorMessage?: string
}

export const authenticate = createActionCreator<AuthenticatePayload, void>(AuthenticateActionType)

// type of `authenticate()`:
// (payload?: AuthenticatePayload | undefined, meta?: void | undefined)
//   => FluxStandardAction<AuthenticatePayload, void>

I would like to enable --noUnusedLocals but the "export types can't be named" issue keep preventing me from doing so.

Above is a simple scenario that involved a higher order function createActionCreator().
The logic is pretty simple and they function it returns is not hard to understand either.

If I turn on --noUnusedLocals, the consume.ts will fail because FluxStandardAction is not explicitly used.
But if I explicitly define the type of const authenticate, it is very redundant.

On one hand, the author of createActionCreator() may create a type for the return value to fix this:

export type ActionCreator = <Payload, Meta>(payload?: Payload, meta?: Meta)
  => FluxStandardAction<Payload, Meta>

// consume.ts
import { createActionCreator, ActionCreator } from './actions'

...
const authenticate: ActionCreator
  = createActionCreator<AuthenticatePayload, void>(AuthenticateActionType)

However, not all package authors would do that, leaving the consumer with very verbose code with not much value gain, IMO.

As an alternative, maybe we can have an inline comment to disable checks for that particular import?

import {
  // ts:disable-next-line noUnusedLocals
  FluxStandardAction,
  ... } from './actions'

...

[mhegazy]

Should not this be covered by #9944?

[unional]

If we are going to resolve #9944 by auto-import and eliminating the need for this extra import, then yes. It will be covered.

On the other hand, I think the above code discover a bug. As I think of it, const authenticate: ActionCreator = ... should not work because it internally still uses FluxStandardAction and it is still not named. So I guess this code will blow up when imported as a library?

It is currently compiles fine.

[mhegazy]

Suppressing --noUnusedLocals errors based on what the declaration emitter needs seems like a very complicated task. I would say #9944 should solve this.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.