Invalid error message about lifetimes when pattern matching with constants

[netvl]

On the latest nightly (previously it worked fine) Rust fails to compile this code:

pub struct Namespace(pub HashMap<Option<String>, String>);

impl Namespace {
...
    pub fn is_essentially_empty(&self) -> bool {
        let Namespace(ref hm) = *self;
        for (k, v) in hm.iter() {
            match (k.as_ref().map(|k| k.as_slice()), v.as_slice()) {
                (None, NS_EMPTY_URI) |
                (Some(NS_XMLNS_PREFIX), NS_XMLNS_URI) |
                (Some(NS_XML_PREFIX), NS_XML_URI) => {},
                _ => return false
            }
        }
        true
    }
...
}

It emits this error message:

   Compiling rust-xml v0.1.0 (file:///home/dpx-infinity/dev/lang/rust/projects/rust-xml)
src/namespace.rs:41:23: 41:29 error: cannot infer an appropriate lifetime for pattern due to conflicting requirements
src/namespace.rs:41         let Namespace(ref hm) = *self;
                                          ^~~~~~
src/namespace.rs:43:54: 43:55 note: first, the lifetime cannot outlive the expression at 43:53...
src/namespace.rs:43             match (k.as_ref().map(|k| k.as_slice()), v.as_slice()) {
                                                                         ^
src/namespace.rs:43:54: 43:55 note: ...so that pointer is not dereferenced outside its lifetime
src/namespace.rs:43             match (k.as_ref().map(|k| k.as_slice()), v.as_slice()) {
                                                                         ^
src/namespace.rs:42:23: 42:25 note: but, the lifetime must be valid for the expression at 42:22...
src/namespace.rs:42         for (k, v) in hm.iter() {
                                          ^~
src/namespace.rs:42:23: 42:25 note: ...so that pointer is not dereferenced outside its lifetime
src/namespace.rs:42         for (k, v) in hm.iter() {
                                          ^~

I managed to strip it down to this example:

const X: &'static str = "12345";

pub fn test(s: String) -> bool {
    match s.as_slice() {
        X => true,
        _ => false
    }
}

It fails to compile with this error:

/tmp/rs/lifetimes/src/lib.rs:18:11: 18:12 error: `s` does not live long enough
/tmp/rs/lifetimes/src/lib.rs:18     match s.as_slice() {
                                          ^
note: reference must be valid for the static lifetime...
/tmp/rs/lifetimes/src/lib.rs:17:32: 22:2 note: ...but borrowed value is only valid for the block at 17:31
/tmp/rs/lifetimes/src/lib.rs:17 pub fn test(s: String) -> bool {
/tmp/rs/lifetimes/src/lib.rs:18     match s.as_slice() {
/tmp/rs/lifetimes/src/lib.rs:19         X => true,
/tmp/rs/lifetimes/src/lib.rs:20         _ => false
/tmp/rs/lifetimes/src/lib.rs:21     }
/tmp/rs/lifetimes/src/lib.rs:22 }

If X => is replaced with "12345" =>, then it compiles fine, so the error seems to be related to matching on consts.

@netvl Sorry for the breakage, fix on its way.