Description
#![allow(incomplete_features)]
#![feature(const_generics)]
use std::mem;
pub trait Trait {
type Associated : Sized;
fn associated_size(&self) -> usize {
[0u8; mem::size_of::<Self::Associated>()];
0
}
}
fn main() {
}
results in:
error: internal compiler error: src/librustc_traits/normalize_erasing_regions.rs:34: could not fully normalize `fn() -> usize {std::mem::size_of::<<Self as Trait>::Associated>}`
thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:889:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: rustc 1.42.0-nightly (da3629b05 2019-12-29) running on x86_64-unknown-linux-gnu
error: aborting due to previous error
Removing the const_generics feature flag gets the expected error message:
error[E0220]: associated type `Associated` not found for `Self`
--> normalize-err.rs:10:36
|
10 | [0u8; mem::size_of::<Self::Associated>()];
| ^^^^^^^^^^ associated type `Associated` not found
error: aborting due to previous error
For more information about this error, try `rustc --explain E0220`.
(IIUC that itself is a bug related to #43408)
Using mem::size_of::<Self::Associated>() directly outside of a const-context works, which I guess is something const_generics enables that isn't otherwise allowed.
Finally, the error message is the same whether or not the code is in a provided method or a impl block; I actually ran into the bug in the later.