Cannot relate bound region: ReInfer(53) <= ReLateBound(284, ...

[xcv-]

I was trying out Rust with a sudoku solver and met a bug

It's the git version (compiled two hours ago) running on i686 ArchLinux, this is the -v output:

rustc 0.9-pre (aa4455e 2013-12-06 01:11:18 -0800)
host: i686-unknown-linux-gnu

Compiler output, backtrace and the file I was compiling: https://gist.github.com/xcv-/c0a79259a7b1280578e5

[alexcrichton]

cc @nikomatsakis

[nikomatsakis]

Dup #5121

[pnkfelix]

�Forward-ported example to run on version 0.10-pre (caf17fe 2014-03-21).

Then reduced it down to the following, which still ICE's:

trait Foo<'r> { fn foo(&'r self); }
impl<'r> Foo<'r> for () { fn foo(&'r self) { fail!("placeholder"); } }

fn check<'a, F: Foo<'a>>(cont: &'a F) { cont.foo(); }

fn main() { check(()); }

% rustc /tmp/demo.rs
/tmp/demo.rs:4:41: 4:45 error: internal compiler error: cannot relate bound region: ReScope(43) <= ReEarlyBound(42, 0, a)
/tmp/demo.rs:4 fn check<'a, F: Foo<'a>>(cont: &'a F) { cont.foo(); }
                                                       ^~~~
note: the compiler hit an unexpected failure path. this is a bug.

(but its still a dupe of #5121. I'm just noting this because I am trying to double-check which dupes of #5121 are still reproducible.)