Arrow functions treated differently than functions and methods #29520

type Test<K extends keyof any> = {
  [P in K | "foo"]: P extends "foo" ? true : () => any
}

function test<T extends Test<keyof T>>(arg: T) {
    return arg;
}

const res1 = test({
  foo: true,
  bar() {
    // Notice the type param of `test` is inferred as `Test<never>`
  }
})

const res2 = test({
  foo: true,
  bar: function () {
    // Same error here.
  }
})

const res3 = test({
  foo: true,
  bar: () => {
    // This is fine.
  }
})