facebook/relay

Are the Result<T, Error> type definitions wrong?

tobias-tengler opened this issue · 5 comments

tobias-tengler commented

I wanted to play around with @catch and noticed that the Flow / TypeScript types and the compiler generated errors passed to the Result type don't make much sense.

The compiler will generate the following code:

export type FooQuery$data = {|
  +me: Result<?{|
    +firstName: ?string,
    +lastName: ?string,
  |}, $ReadOnlyArray<mixed>>,
|};

so the error type is $ReadOnlyArray<mixed>.

The type definitions in relay-runtime define the errors field on the ErrorResult as a $ReadOnlyArray<Error>:
https://github.com/facebook/relay/blob/e357063c26d0aaf0a5027ba591138ad172cd103f/packages/relay-runtime/experimental.js#L46C2-L55C67

So you'd end up with the ErrorResult.errors being Array<Array<Error>>. This doesn't seem right to me?

captbaritone commented

Maybe this is a bug where we've used a global type Error as the name of a type generic?

itamark commented

@captbaritone I think @tobias-tengler hunch might be correct. That the generated FooQuery$data here should be

export type FooQuery$data = {|
  +me: Result<?{|
    +firstName: ?string,
    +lastName: ?string,
  |}, mixed,
|};
captbaritone commented

I see, I missed the point. Array<Array<Error>>. Yeah, looks like a bug in the types.

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