Stack overflow with specialization enabled

#![feature(specialization)]

trait Foo {
    fn foo(&self);
}

trait Bar {
    fn bar(&self);
}

impl<T> Bar for T where T: Foo {
    fn bar(&self) {}
}

impl<T> Foo for T where T: Bar {
    fn foo(&self) {}
}

impl Foo for u64 {}

fn main() {
}

Compiling this code results in:

thread 'rustc' has overflowed its stack
fatal runtime error: stack overflow

There is no backtrace.

If I disable specialization feature, rustc reports an error:

error[E0119]: conflicting implementations of trait `Foo` for type `u64`

Rustc details:

rustc 1.17.0-nightly (0648517fa 2017-02-03)
binary: rustc
commit-hash: 0648517faf1e2cf37c8b6770cbd0180a816ed9a0
commit-date: 2017-02-03
host: x86_64-unknown-linux-gnu
release: 1.17.0-nightly
LLVM version: 3.9

[zmt00]

This seems to compile as of the most recent nightly.

[-@- rust]$ cat foo.rs
#![feature(specialization)]
trait Foo {
    fn foo(&self);
}
trait Bar {
    fn bar(&self);
}
impl<T> Bar for T where T: Foo {
    fn bar(&self) {}
}
impl<T> Foo for T where T: Bar {
    fn foo(&self) {}
}
impl Foo for u64 {}
fn main() {
}
[-@- rust]$ rustc foo.rs
[-@- rust]$ rustc --version --verbose
rustc 1.28.0-nightly (5d0631a64 2018-05-30)
binary: rustc
commit-hash: 5d0631a6438cf30cac236b7176371663e35c8d07
commit-date: 2018-05-30
host: x86_64-unknown-linux-gnu
release: 1.28.0-nightly
LLVM version: 6.0

Good to hear that!

Would it make sense to add this example to the test suite to prevent regressions in the future?