@mut freezing bugs

[thestinger]

You can unfreeze with a temporary borrowed pointer, because it doesn't restore the previous state:

fn main() {
    let x = @mut 5;

    let a = &*x;
    {
        let b = &*x;
    }
    let c = &mut *x;
}

Mutable borrows aren't tracked:

fn main() {
    let x = @mut 5;

    let a = &mut *x;
    let b = &mut *x;
    let c = &*x;
}

I think freezing needs to be enum Borrow { Mutable, Immutable, Nothing } with an immutable borrow failing if there was a Mutable one, and a mutable borrow failing on any freeze.

[nikomatsakis]

Yeah, this code is not really right. I have some parts of this fixed in my borrow checker branch, and I've started a branch to take care of the rest.

[nikomatsakis]

These issues are resolved. See the following run-pass and run-fail tests:

run-pass:
borrowck-wg-borrow-mut-to-imm-2.rs
borrowck-wg-borrow-mut-to-imm-3.rs
borrowck-wg-borrow-mut-to-imm.rs
borrowck-wg-simple.rs
borrowck-wg-two-imm-borrows.rs

run-fail:
borrowck-wg-fail-2.rs
borrowck-wg-fail-3.rs
borrowck-wg-fail.rs
borrowck-wg-imm-then-mut.rs
borrowck-wg-mut-then-imm.rs
borrowck-wg-one-mut-one-imm.rs
borrowck-wg-one-mut-one-imm-slice-method.rs
borrowck-wg-one-mut-one-imm-slices.rs
borrowck-wg-two-array-indices.rs