I'll try to submit a report later. It's exactly what it sounds like, though.

    $ cat hello.rs
    fn main() {
	println!("Hello world!");
    }
    $ lldb -v
    lldb-350.0.21.9
    $ uname -a
    Darwin mycomp 15.5.0 Darwin Kernel Version 15.5.0: Tue Apr 19 18:36:36 PDT 2016; root:xnu-3248.50.21~8/RELEASE_X86_64 x86_64
    $ rustc --version
    rustc 1.8.0
    $ rustc -g hello.rs
    $ ./hello
    Hello world!
    $ lldb hello
    (lldb) target create "hello"
    Current executable set to 'hello' (x86_64).
    (lldb) source list
    (lldb)
    (lldb) b 2
    error: No selected frame to use to find the default file.
    error: No file supplied and no default file available.

I don't see how the core team could be unaware of this unless literally no one has done even a cursory glance at OS X & LLDB in months.

I think this is a known issue relating to some lldb versions no longer treating unknown languages as C; which got fixed in lldb upstream but may not have been released yet.

Well, I do use it regularly for testing Servo. There's a debugger harness run as part of the test suite too. (Not to say we shouldn't fix whatever is causing your problem, though!)

I can make it work if I feed full file paths to the debugger using syntax I can't remember off the top of my head. Maybe that's one way some scripts might be functioning?

I'll copy and past this into a Github issue when I have a sec.

edit: https://github.com/rust-lang/rust/issues/33674

Thanks! Forwarding to the appropriate people.