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.