GLB of two regions is computed incorrectly

[nikomatsakis]

This test case which came up in discussions of #3166 revealed a bug in our GLB computation. It successfully compiles but should not. The expected error is in the function set_desc(), which combines &self with &---this should yield a lifetime of only the body of the function itself, since that is the only lifetime that the two lifetime parameters are guaranteed to have in common, but it currently yields &. Wrong!

mod argparse {
    use std;

    import std::map;
    import either::{either, left, right};

    struct Flag {
        name: &str;
        desc: &str;
        max_count: uint;
        mut value: uint;
    }

    fn flag(name: &str, desc: &str) -> Flag {
        Flag { name: name, desc: desc, max_count: 1, value: 0 }
    }

    impl Flag {
        fn set_desc(self, s: &str) -> Flag {
            Flag {
                name: self.name,
                desc: s,
                max_count: self.max_count,
                value: self.value
            }
        }
    }
}

fn main () {
    let f : argparse::Flag = argparse::flag(~"flag", ~"My flag");
    let updated_flag = f.set_desc(~"My new flag");
    assert updated_flag.desc == "My new flag";
}

I have a fix underway.

[nikomatsakis]

Fixed now.