Feature request: warn on unused result

[krisselden]

It can be easy to forget an await for a method returning Promise<void> and have your code appear to work.

I would be nice to have something like must_use in Rust or the __attribute__((warn_unused_result)) in C or @warn_unused_result in Swift.

[krisselden]

This is my same struggle #13376

[mhegazy]

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

[dannycochran]

Can this be re-opened? I think having a "warn_on_unused" annotation is actually different than #13376.

There are plenty of non-async cases where you'd want to be warned about an unused result, for instance with redux.

const someActionCreator = (payload: string) => ({
  type: SOME_ACTION,
  payload
});

const someAction = () => (dispatch) => {
  // Compute the payload...
  const payload = 'foo.bar';
  // The correct way:
  // dispatch(someActionCreator(payload));

  // What can easily happen:
  someActionCreator(payload);
};

const onTouchTarget = () => this.props.dispatch(someAction());

This could be solved a number of ways, but a decorator seems pretty natural:

@warn_unused_result
const someActionCreator = (payload: string):  => ({
  type: SOME_ACTION,
  payload
});

[krisselden]

this was mistakenly marked as a duplicate of #13376 that was the reason I had that motivated me opening this, but this feature is used in other languages for many reasons and is more generalized than #13376

[RyanCavanaugh]

There's another issue I can't find at the moment that covers non-discardable function return values

[mhegazy]

tracked now by #8584