Possible regression: Updating 2.8.0 to 2.9.0 causes "type annotations needed" for `BTreeSet::range` etc. about rust-ordered-float

[mbrubeck]

Hmm, this was caused by #98.

[mbrubeck]

The BTreeSet::range method is generic over a type K: Ord where T: Borrow<K> + Ord. So it seems plausible that adding a new Borrow implementation to NotNan could allow calling this function with additional types.

However, NotNan<f64> only implements Borrow<f64>, and f64 does not implement Ord. So it should not affect this function call. It seems the compiler is not smart enough to see this, or it is overly conservative since it believes that f64 might implement Ord in the future. I'm not sure which.

[mbrubeck]

Closed accidentally. I meant to close #91, not this one.

[TonalidadeHidrica]

The workaround is to explicitly specify the type parameter K.

use std::collections::BTreeSet;
use ordered_float::NotNan;

fn main() {
    let a = BTreeSet::<NotNan<f64>>::new();
    let b = a.range::<NotNan<f64>, _>(..);
}

[TonalidadeHidrica]

Isn't it strange that implementing a trait make type inference fail? I'm wondering if this tends to happen, or it is a bug (or something can be improved) of Rust compiler.