Let pattern matching on tuple structs broken for double generic functions.

[nightpool]

The demo code from Closed01 doesn't compile.

use std::rand::{Closed01, random};

fn main() {
    let Closed01(val) = random::<Closed01<f32>>();
    println!("{} is a random number between 0 and 1!", val);
}

The compiler gives an error message of

error: mismatched types: expected `std::rand::Closed01<f32>` but found 
`std::rand::Closed01<BUG[0u]>` (expected f32 but found type parameter)

@huonw found a workaround by wrapping it in a function:
rust fn extract<T>(Closed01(x): Closed01<T>) -> T { x }

I'm not sure what exactly is going on here, but I'm guessing it has something to do with the double generic function <Closed01> and let pattern matching for tuple structs.

[jfager]

This looks like its no longer an issue, just needs a test.