Inference regression on nightly

[vickenty]

This works on stable and beta, fails to compile on nightly.

(Playground)

trait Make {
    fn make() -> Self;
}

impl Make for f64 {
    fn make() -> f64 {
        1.0
    }
}

fn make_value<T: Make>() -> T {
    T::make()
}

fn main() {
    let mut sum = 0.0;
    
    let val = make_value();
    sum += val;
    
    println!("{:}", sum);
}

error[E0282]: type annotations needed
  --> src/main.rs:18:9
   |
18 |     let val = make_value();
   |         ^^^
   |         |
   |         cannot infer type for `_`
   |         consider giving `val` a type

Versions tried:

rustc 1.20.0 (f3d6973f4 2017-08-27) - works
rustc 1.21.0-beta.3 (ea1fd7d42 2017-09-15) - works
rustc 1.22.0-nightly (185cc5f26 2017-10-02) - fails

[leonardo-m]

See also: #44973

[vickenty]

Extensive discussion of this happened in #41336 and #44287.

[leonardo-m]

Extensive discussion of this happened in #41336 and #44287.

I've read part of those, and the list of regressions they are listing is exactly the many problems I'm seeing in my code. Apparently I hit every one of them :-) So I guess this breakage is expected and we should close down this issue and #44973 too...

[nikomatsakis]

Closing as expected due to this comment.

cc @rust-lang/libs more fallout from #41336