Change:
I was playing around with some code which can be found and is attached below. When I click on output I get the following output: I don't have a rust installation locally right now, so I cannot create the backtrace. I'll add it later today. The code which triggers this:
Stack trace: (There is no ICE with (nothing generated either due to type error). Perhaps playpen should use instead.)
You can get backtrace on playpen here: !
Looks like this has been fixed recently

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>