microsoft / microsoft/TypeScript

[bug] A method return type of 'this' is incorrectly converted to 'any' in declaration output

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Bug Domain: Declaration Emit
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Description

TypeScript Version: ^3.3.0-dev.20181129

Code

import * as events from 'events'

// EventArgs is used to create the event payload arguments for methods like
// EventEmitter.emit. This makes it possible to require a payload argument if
// the type is not `undefined`, or to not require an event payload argument if
// the type is `undefined`.
type EventArgs<
  EventTypes,
  K extends keyof EventTypes
> = EventTypes[K] extends undefined ? [] : [EventTypes[K]]

// our own version of EventEmitter with type-safe events (because the
// @types/node definition makes all events type `any`).
export interface IEventEmitter<EventTypes> {
  new (): IEventEmitter<EventTypes>

  addListener<EventName extends keyof EventTypes>(
    event: EventName,
    listener: (...args: EventArgs<EventTypes, EventName>) => void,
  ): this

  on<EventName extends keyof EventTypes>(
    event: EventName,
    listener: (...args: EventArgs<EventTypes, EventName>) => void,
  ): this

  once<EventName extends keyof EventTypes>(
    event: EventName,
    listener: (...args: EventArgs<EventTypes, EventName>) => void,
  ): this

  removeListener<EventName extends keyof EventTypes>(
    event: EventName,
    listener: (...args: EventArgs<EventTypes, EventName>) => void,
  ): this

  removeAllListeners<EventName extends keyof EventTypes>(
    event?: EventName,
  ): this

  emit<EventName extends keyof EventTypes>(
    event: EventName,
    ...args: EventArgs<EventTypes, EventName>
  ): boolean

  eventNames<EventName extends keyof EventTypes>(): Array<EventName>
  setMaxListeners(n: number): this
  getMaxListeners(): number

  listeners<EventName extends keyof EventTypes>(
    event: EventName,
  ): (...args: EventArgs<EventTypes, EventName>) => void[]

  listenerCount<EventName extends keyof EventTypes>(type: EventName): number

  prependListener<EventName extends keyof EventTypes>(
    event: EventName,
    listener: (...args: EventArgs<EventTypes, EventName>) => void,
  ): this

  prependOnceListener<EventName extends keyof EventTypes>(
    event: EventName,
    listener: (...args: EventArgs<EventTypes, EventName>) => void,
  ): this
}

// This creates an EventEmitter class that uses our type definition. The
// implementation still comes from Node's EventEmitter.
//
// eslint-disable-next-line typescript/explicit-function-return-type
export function makeEventEmitterClass<EventTypes>() {
  // merge the IEventEmitter interface and EventEmitter as IEventEmitter
  // implementation into one.
  // XXX Is there a better way?
  const EventEmitter = class
    extends ((events.EventEmitter as unknown) as IEventEmitter<EventTypes>) {}
    // implements IEventEmitter<EventTypes> {}

  return EventEmitter
}

Expected behavior:

Declaration file should not use any for method return types that return this.

I expect output like the following:

declare type EventArgs<EventTypes, K extends keyof EventTypes> = EventTypes[K] extends undefined ? [] : [EventTypes[K]];
export interface IEventEmitter<EventTypes> {
    new (): IEventEmitter<EventTypes>;
    addListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    on<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    once<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    removeListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    removeAllListeners<EventName extends keyof EventTypes>(event?: EventName): IEventEmitter<EventTypes>;
    emit<EventName extends keyof EventTypes>(event: EventName, ...args: EventArgs<EventTypes, EventName>): boolean;
    eventNames<EventName extends keyof EventTypes>(): Array<EventName>;
    setMaxListeners(n: number): IEventEmitter<EventTypes>;
    getMaxListeners(): number;
    listeners<EventName extends keyof EventTypes>(event: EventName): (...args: EventArgs<EventTypes, EventName>) => void[];
    listenerCount<EventName extends keyof EventTypes>(type: EventName): number;
    prependListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    prependOnceListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
}
export declare function makeEventEmitterClass<EventTypes>(): {
    new (): {
        new (): IEventEmitter<EventTypes>;
        addListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
        on<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
        once<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
        removeListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
        removeAllListeners<EventName extends keyof EventTypes>(event?: EventName | undefined): IEventEmitter<EventTypes>;
        emit<EventName extends keyof EventTypes>(event: EventName, ...args: EventArgs<EventTypes, EventName>): boolean;
        eventNames<EventName extends keyof EventTypes>(): EventName[];
        setMaxListeners(n: number): IEventEmitter<EventTypes>;
        getMaxListeners(): number;
        listeners<EventName extends keyof EventTypes>(event: EventName): (...args: EventArgs<EventTypes, EventName>) => void[];
        listenerCount<EventName extends keyof EventTypes>(type: EventName): number;
        prependListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
        prependOnceListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    };
    addListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    on<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    once<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    removeListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    removeAllListeners<EventName extends keyof EventTypes>(event?: EventName | undefined): IEventEmitter<EventTypes>;
    emit<EventName extends keyof EventTypes>(event: EventName, ...args: EventArgs<EventTypes, EventName>): boolean;
    eventNames<EventName extends keyof EventTypes>(): EventName[];
    setMaxListeners(n: number): IEventEmitter<EventTypes>;
    getMaxListeners(): number;
    listeners<EventName extends keyof EventTypes>(event: EventName): (...args: EventArgs<EventTypes, EventName>) => void[];
    listenerCount<EventName extends keyof EventTypes>(type: EventName): number;
    prependListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    prependOnceListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
};
export {};
//# sourceMappingURL=index.d.ts.map

Actual behavior:

Example of wrong output:

declare type EventArgs<EventTypes, K extends keyof EventTypes> = EventTypes[K] extends undefined ? [] : [EventTypes[K]];
export interface IEventEmitter<EventTypes> {
    new (): IEventEmitter<EventTypes>;
    addListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): this;
    on<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): this;
    once<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): this;
    removeListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): this;
    removeAllListeners<EventName extends keyof EventTypes>(event?: EventName): this;
    emit<EventName extends keyof EventTypes>(event: EventName, ...args: EventArgs<EventTypes, EventName>): boolean;
    eventNames<EventName extends keyof EventTypes>(): Array<EventName>;
    setMaxListeners(n: number): this;
    getMaxListeners(): number;
    listeners<EventName extends keyof EventTypes>(event: EventName): (...args: EventArgs<EventTypes, EventName>) => void[];
    listenerCount<EventName extends keyof EventTypes>(type: EventName): number;
    prependListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): this;
    prependOnceListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): this;
}
export declare function makeEventEmitterClass<EventTypes>(): {
    new (): {
        new (): IEventEmitter<EventTypes>;
// RIGHT HERE, the next lines have 'any'
        addListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): any;
        on<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): any;
        once<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): any;
        removeListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): any;
        removeAllListeners<EventName extends keyof EventTypes>(event?: EventName | undefined): any;
        emit<EventName extends keyof EventTypes>(event: EventName, ...args: EventArgs<EventTypes, EventName>): boolean;
        eventNames<EventName extends keyof EventTypes>(): EventName[];
        setMaxListeners(n: number): any;
        getMaxListeners(): number;
        listeners<EventName extends keyof EventTypes>(event: EventName): (...args: EventArgs<EventTypes, EventName>) => void[];
        listenerCount<EventName extends keyof EventTypes>(type: EventName): number;
        prependListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): any;
        prependOnceListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): any;
    };
    addListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    on<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    once<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    removeListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    removeAllListeners<EventName extends keyof EventTypes>(event?: EventName | undefined): IEventEmitter<EventTypes>;
    emit<EventName extends keyof EventTypes>(event: EventName, ...args: EventArgs<EventTypes, EventName>): boolean;
    eventNames<EventName extends keyof EventTypes>(): EventName[];
    setMaxListeners(n: number): IEventEmitter<EventTypes>;
    getMaxListeners(): number;
    listeners<EventName extends keyof EventTypes>(event: EventName): (...args: EventArgs<EventTypes, EventName>) => void[];
    listenerCount<EventName extends keyof EventTypes>(type: EventName): number;
    prependListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
    prependOnceListener<EventName extends keyof EventTypes>(event: EventName, listener: (...args: EventArgs<EventTypes, EventName>) => void): IEventEmitter<EventTypes>;
};
export {};
//# sourceMappingURL=index.d.ts.map

This caused chaining method calls in my app not to work.

Playground Link: N/A

Related Issues:

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the issue with TypeScript 3.3.0-dev.20181129 using the supplied IEventEmitter and makeEventEmitterClass example, then compare the emitted declaration output. Trace declaration generation for the inferred method return types; done means the generated methods preserve the IEventEmitter return type instead of any, with regression coverage for this case.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
30/100

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