Moves into patterns (also irrefutable patterns) always copy

[nikomatsakis]

The following test:

struct foo {
    x: int;

    new(x: int) {
        self.x = x;
    }

    drop {
        error!{"Hello, world!"};
    }
}

fn main() {
    let x = ~foo(1);
    error!{"x.x: %d", x.x};
    let ~y <- x;
    error!{"y.x: %d", y.x};

    alt move y {
      copy z {}
    }
}

prints Hello World! three times. I think that patterns (both refutable/irrefutable, which are different code paths) just always copy in trans.

[nikomatsakis]

Also, the copy keyword on the pattern (right now) just makes it into "value mode". It shouldn't be necessary eventually and should in fact produce a warning.

[catamorphism]

I'm going to take this as part of #3271. Hopefully @nikomatsakis won't mind ;-)

[catamorphism]

As of 563aa0b , the copy keyword in the pattern does in fact produce an error.

[pcwalton]

Closing this. Please reopen if this is still an issue.