Function expression or method is not inferable when we have mapped type with a conditional type

🔎 Search Terms

conditional method arrow function

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ

⏯ Playground Link

Playground Link

💻 Code

type Map<T> =  { 
  readonly [P in keyof T]: T[P] extends boolean ? "boolean":  "other"
} 
export function buildCommand<F extends Record<string, unknown>>(builderArgs: { 
  func: (p: F) => void
  params: Map<NoInfer<F>>
}) {

}
type Foo = { foo: boolean };
// Function expression does not work
buildCommand({
  func: function (p: Foo) { },
  params: {
    foo: "boolean"
  }
})

// Methods don't work
buildCommand({
  func(p: Foo) { },
  params: {
    foo: "boolean"
  }
})

// Arrow function works
buildCommand({
  func: (p: Foo) => { },
  params: {
    foo: "boolean"
  }
})

🙁 Actual behavior

For the first two calls we get an error while the third one is successful

🙂 Expected behavior

All three calls should be successful

Additional information about the issue

Removing the constraint from F (Playground Link) or changing it to F extends Record<keyof F, unknown> (Playground Link) will remove the error.

Commencez par la reproduction liée dans TypeScript Playground et comparez l’inférence pour les cas d’expression de fonction, de méthode et de fonction fléchée sous la contrainte Record<string, unknown>. C’est terminé lorsque les trois appels à buildCommand sont acceptés tout en préservant le comportement signalé lorsque la contrainte est supprimée ou modifiée.