Failing to understand a rust generic function erro

Question

This question already has an answer here:

• Expected type parameter, found u8, but the type parameter is u8 2 answers

I was trying to get a piece of Rust generic code to compile, and after mucking around for while narrowed it down to failure of this code to compile. I am not sure what exactly is breaking down here (E0308 doesn't help me much) -- I must be missing something silly:

fn is_fail<bool>() -> bool { false }
fn main(){
  let failure:bool = is_fail();
  //if ! failure {
    println!("{}", failure);
  //}
}

The error is:

error: mismatched types [--explain E0308]
 --> <anon>:1:30
1 |> fn is_fail<bool>() -> bool { false }
  |>                              ^^^^^ expected type parameter, found bool
note: expected type `bool`
note:    found type `bool`

Answer 1

In your function the type parameter bool shadows the builtin type bool. So your function declaration is essentially the same as

fn is_fail<T>() -> T { false }

which clearly isn't well-typed.