Make trait lifetime parameters early bound in static fn type.

[nikomatsakis]

Make trait lifetime parameters early bound in static fn type. Reasoning for this change is (hopefully) explained well enough in the comment, so I'll not duplicate it here. Fixes #10391.

r? @pnkfelix

[pnkfelix]

same comments as on #10556 about using a different syntax for the primed type-vars. But I assume you will fix that eventually, it need not hold up this patch...

[dwrensha]

I am eagerly awaiting this patch! Unfortunately, it looks like traits with lifetime parameters do not work across crate boundaries.

After applying this patch, I tried compiling the following two crates:

// other.rs

#[link(name = "other", package_id = "other", vers="0.0")];
#[crate_type = "lib"];

pub enum Value<'v> {
    A(&'v str),
    B,
}

pub trait Decoder<'v> {
    fn read(&mut self) -> Value<'v>;
}

pub trait Decodable<'v, D: Decoder<'v>> {
    fn decode(d: &mut D) -> Self;
}

// main.rs

extern mod other;

struct S;

impl<'v, D: other::Decoder<'v>> other::Decodable<'v, D> for S {
    fn decode(d: &mut D) -> S {
        match d.read() {
            other::A(..) => S,
            other::B => other::Decodable::decode(d),
        }
    }
}

fn main (){}

The result:

$ rustc other.rs
$ rustc main.rs -L.
main.rs:7:12: 7:29 error: wrong number of lifetime parameters: expected 0 but found 1
main.rs:7 impl<'v, D: other::Decoder<'v>> other::Decodable<'v, D> for S {
                      ^~~~~~~~~~~~~~~~~
main.rs:7:32: 7:55 error: wrong number of lifetime parameters: expected 0 but found 1
main.rs:7 impl<'v, D: other::Decoder<'v>> other::Decodable<'v, D> for S {
                                          ^~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 2 previous errors

[dwrensha]

Aha! This patch appears to fix that problem:
dwrensha@c746bd8

I'd submit a pull request now, but I'd want to include a test case and try it locally, and "make check" is currently broken for me. :/

[dwrensha]

Update: I got make check working and submitted a pull request for the cross-crate trait problem. #10813

[nikomatsakis]

@dwrensha great! I've been meaning to look into your example to try and figure out what the problem was :)