ICE with generic associated types

[Patryk27]

Hi,

Following code:

#![feature(generic_associated_types)]

trait Iterator {
    type Item<'a>: 'a;
}

... fails with:

error: internal compiler error: Region parameter out of range when substituting in region 'a (root type=None) (index=1)

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:362:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

error: internal compiler error: unexpected panic

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 1.37.0-nightly (b25ee6449 2019-06-17) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type lib

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `playground`.

To learn more, run the command again with --verbose.

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=ba801a17c109844b79633bb40919c4fc

[hellow554]

Good catch. Without the feature gate it does not crash on beta or nightly, but only on stable. With feature gate it does crash on all three versions.

@rustbot modify labels: C-bug T-compiler I-ICE A-associated-items

[pnkfelix]

(closing as duplicate of issue #62521, as it has a more informative title. I did consider trying to reuse this ticket as the main representative instead, but at this point closing this as duplicate is cleaner overall in terms of conveying the metabug-like nature of #62521.)