Change:
Playground Output: Other example (possibly different bug): Output:
I just got the same ICE on linux with both the and builds. My case is essentially the same. You create an iterator of references to sub-elements of some thing which has been passed in by reference. The compiler should figure out that the iterator can only live as long as the original object, but ICEs instead. ()

Discussion:
<ins> // Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. struct Foo; fn main() { || if let Foo::NotEvenReal() = Foo {}; //~ ERROR E0599 } </ins>

<ins> // Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. // #29924 #![feature(const_fn, associated_consts)] trait Trait { const N: usize; } impl Trait { //~^ ERROR the trait `Trait` cannot be made into an object [E0038] const fn n() -> usize { Self::N } } fn main() {} </ins>

<ins> // Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. // #39872, #39553 #![feature(conservative_impl_trait)] fn will_ice(something: &u32) -> impl Iterator<Item = &u32> { //~^ ERROR the trait bound `(): std::iter::Iterator` is not satisfied [E0277] } fn main() {} </ins>

<ins> // Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. fn main() { let a = std::sys::imp::process::process_common::StdioPipes { ..panic!() }; //~^ ERROR failed to resolve. Could not find `imp` in `sys` [E0433] //~^^ ERROR module `sys` is private [E0603] } </ins>

<ins> // Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. fn iterate<T, F>(initial: T, f: F) -> Iterate<T, F> { Iterate { state: initial, f: f, } } pub struct Iterate<T, F> { state: T, f: F } impl<T: Clone, F> Iterator for Iterate<T, F> where F: Fn(&T) -> T { type Item = T; #[inline] fn next(&mut self) -> Option<Self::Item> { self.state = (self.f)(&self.state); Some(self.state.clone()) } #[inline] fn size_hint(&self) -> (usize, Option<usize>) { (std::usize::MAX, None) } } fn main() { let a = iterate(0, |x| x+1); println!("{:?}", a.iter().take(10).collect::<Vec<usize>>()); //~^ ERROR no method named `iter` found for type `Iterate<{integer} } </ins>

<ins> // Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. // #39665 #![feature(conservative_impl_trait)] fn batches(n: &u32) -> impl Iterator<Item=&u32> { std::iter::once(n) } fn main() {} </ins>

<ins> // Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. trait VecN { const DIM: usize; } trait Mat { type Row: VecN; } fn m<M: Mat>() { let x = M::Row::DIM; } fn main() {} </ins>