Incorrectly typed argument variant

TypeScript Version: 3.8.3

Search Terms:

Parameters, Array, Overloading, Type inference

Code

type VariantA = [(err: Error, data: string) => any]
type VariantB = [(data: string) => any, (err: Error) => any]
type Args = VariantA | VariantB
 
function fn (...rest: Args): void { /* do something */ }

fn((err, data) => {
  err.stack // Correct: Typed as Error
  data.charAt(0) // Correct: Typed as string
})

fn((data) => {
  data //  --> Error: Mistyped as any, should be string  <--
}, (err) => {
  err.stack // Correct: Typed as Error
})

Expected behavior:

If two functions are passed in (VariantB), the first paramter should be typed as data: string.

Actual behavior:

If two functions are passed in, the first function's parameter is typed as any.

Inizia con la riproduzione minima in TypeScript nell’issue e confronta il contextual typing delle chiamate con un callback e con due callback. Segui l’inferenza dei tipi e la gestione degli overload per il union rest parameter, quindi verifica che il primo parametro del callback venga inferito come string senza introdurre regressioni nei typings di Error e data.