Must check mutability when instantiating impl &T methods

[bblum]

Here is some code that segfaults.

If I replace the impl with fn with(x: &X, blk: fn(...)) then the program is correctly rejected.

import either::*;
enum X = Either<(uint,uint),fn()>;
impl &X {
    fn with(blk: fn(x: &Either<(uint,uint),fn()>)) {
        blk(&**self)
    }
}
fn main() {
    let mut x = X(Right(main));
    do (&mut x).with |opt| {  // this should be illegal
        match *opt {
            Right(f) => {
                x = X(Left((0,0)));
                f()
            },
            _ => fail
        }
    }
}

[bblum]

I believe @nikomatsakis commented earlier that this is a bug with auto-ref and auto-deref mixing.

[nikomatsakis]

Will be fixed as part of #3443. @bblum are there other issues you know of that seem to be related to autoref?

[bblum]

I don't think I found any... but it might pay off to enumerate a bunch of different combinations like this one.