A way to make custom error messages for types

CustomErrorMessages.ts

type ValidateType<T extends string> =
    T extends 'bad' ? 'Error message'
    : T extends 'another bad' ? 'Another error message'
    : T extends 'Error message' | 'Another error message' ? `Can't use '${ T }'`
    : T

function fn<T extends string> ( arg: ValidateType<T> ) { }

fn( 'this should work' ) // works
fn( 'bad' ) // Argument of type '"bad"' is not assignable to parameter of type '"Error message"'.
fn( 'another bad' ) // Argument of type '"another bad"' is not assignable to parameter of type '"Another error message"'.
fn( 'Error message' ) // Argument of type '"Error message"' is not assignable to parameter of type '"Can't use 'Error message'"'.