Beta regression error "trait ... is not implemented for usize" #56020
Description
Hello,
I have hit this strange error after updating the nightly(and beta) compiler. I tried the code below, this is a minimized version from a larger code base. Here is it on playground.
trait MyIterator { type Item; } trait ObjectTrait { fn size(&self) -> u32; } trait ObjectCollectionTrait<'a> { type ItemType: 'a + ObjectTrait; type Iter: MyIterator<Item = &'a Self::ItemType>; } impl ObjectTrait for u32 { fn size(&self) -> u32 { 0 } } struct ObjectCollection<'a> { collection: &'a ObjectCollectionTrait<'a, ItemType = u32, Iter = MyIterator<Item = &'a u32>> } fn main() {} I am getting this error and I don't know how usize is involved here.
error[E0277]: the trait bound `usize: ObjectCollectionTrait<'a>` is not satisfied --> src/main.rs:21:1 | 21 | / struct ObjectCollection<'a> { 22 | | collection: &'a ObjectCollectionTrait<'a, ItemType = u32, Iter = MyIterator<Item = &'a u32>> 23 | | } |_^ the trait `ObjectCollectionTrait<'a>` is not implemented for `usize` error[E0277]: the trait bound `usize: ObjectCollectionTrait<'a>` is not satisfied --> src/main.rs:25:10 | 25 | impl<'a> ObjectCollection<'a> { | ^^^^^^^^^^^^^^^^^^^^ the trait `ObjectCollectionTrait<'a>` is not implemented for `usize` After bisecting for a while, I discovered the error appears starting with this version of nightly:
$ rustc --version --verbose rustc 1.30.0-nightly (f2302daef 2018-09-12) binary: rustc commit-hash: f2302daef3608c09e2b50193a64611b18ced86f3 commit-date: 2018-09-12 host: x86_64-unknown-linux-gnu release: 1.30.0-nightly LLVM version: 8.0 The build from the day before doesn't show this error (and stable is also fine):
$ rustc --version --verbose rustc 1.30.0-nightly (2f1547c0a 2018-09-11) binary: rustc commit-hash: 2f1547c0aa5957b42cc768c00119c6eb7b4262d3 commit-date: 2018-09-11 host: x86_64-unknown-linux-gnu release: 1.30.0-nightly LLVM version: 8.0