Jerko Steiner
3595a71cec
After spending almost two days in finding the issue, I ran across a few TypeScript issues on their GitHub page: - Loss of type inference converting to named parameters object https://github.com/Microsoft/TypeScript/issues/29791 - Parameter of a callback without a specified type next to it breaks code. https://github.com/Microsoft/TypeScript/issues/29799 - Convert to named parameters https://github.com/Microsoft/TypeScript/pull/30089 It became clear that TypeScript is unable to infer method return arguments if a generic type is used more than once in generic parameter object. Instead it returns {}. For example, the following would fail on line 28: type Convert<A, B> = (value: A) => B interface IParams<C, D> { value: C convert: Convert<C, D> doConvert: (value: C, convert: this['convert']) => D } function doSomething<E, F>(value: E, convert: Convert<E, F>) { return convert(value) } function build<G, H>(params: IParams<G, H>) { const {value, convert} = params return params.doConvert(value, convert) } const outerResult = build({ value: { a: { value: 1, }, b: 'string', }, convert: value => value.a, doConvert: (value, convert) => { const innerResult = doSomething(value, convert) innerResult.value console.log('innerResult:', innerResult) return innerResult }, }) console.log('outerResult:', outerResult) With the message: Property 'value' does not exist on type '{}'. If we replace parameter object IParams with regular ordered function parameters, the compilation succeeds. RyanCavanough (TS project lead) from GitHub commented: > We don't have a separate pass to say "Go dive into the function and > check to see if all its return statements don't rely on its parameter > type" - doing so would be expensive in light of the fact that extremely > few real-world functions actually behave like that in practice. Source: https://github.com/Microsoft/TypeScript/issues/29799#issuecomment-464154659 These modifications bring type safety to TestUtils.tsx, and therefore client-side tests of React components, while keeping almost the same ease of use as before.