Specialization: impl repeats parameter `'source`

Hello there,

I am aware that the specialization feature is still unstable, but I was wondering if there was a way to circumvent my problem.

Here, I would like to implement two specializations of Convert: one for String and one for &str.
While the former works very well, the latter does not compile. Do you know if there is any way such that I could manage to implement Convert for &str specifically?

Thanks in advance!

MWE:

#![feature(min_specialization)]

trait Convert<'source> {
    fn convert(src: &'source str) -> Self;
}

impl<'source, T> Convert<'source> for T 
where T:
    From<&'source str>
{
    default fn convert(src: &'source str) -> Self {
        src.into()
    }
}

impl<'source> Convert<'source> for String {
    default fn convert(src: &'source str) -> Self {
        src.into()
    }
}

impl<'source> Convert<'source> for &'source str {
    default fn convert(src: &'source str) -> Self {
        src.into()
    }
}

fn main() {
    println!("Hello");
}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
error: specializing impl repeats parameter `'source`
  --> src/main.rs:22:1
   |
22 | impl<'source> Convert<'source> for &'source str {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: could not compile `playground` due to previous error