Type inference behaves unexpectedly when dealing with functions that have type parameters

Bug Report

When a function definition a with type parameters is passed as an argument to another function b, b is unable to destructure the parameters of the passed a function.

🔎 Search Terms

type parameter function argument destructure

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about generics

⏯ Playground Link

Playground link with relevant code

💻 Code

type DefaultVariantProps = {
  tabsClassName?: string
}

function fn<P extends {}>(arg1?: (props: P) => void): P {
  return null as any
}

const a = fn(null as any as (props: DefaultVariantProps) => void)
const b = fn(null as any as <T>(props: DefaultVariantProps) => void)

// no problem
a.tabsClassName
// Property 'tabsClassName' does not exist on type '{}'.(2339)
b.tabsClassName

type T1 = (props: DefaultVariantProps) => void
type T2 = <T>(props: DefaultVariantProps) => void

// no problem
type T3 = Parameters<T1>[0]['tabsClassName']
// no problem
type T4 = Parameters<T2>[0]['tabsClassName']

🙁 Actual behavior

When a function definition a with type parameters is passed as an argument to another function b, b is unable to destructure the parameters of the passed a function.
It seems that generics should not cause type inference failures.

🙂 Expected behavior

No error.

Inizia con il TypeScript Playground collegato e l’esempio di codice, confrontando i tipi inferiti di a e b quando la funzione passata ha un parametro di tipo. L’issue è completata quando b.tabsClassName non produce alcun errore, mentre il caso non generico esistente continua a funzionare.