Some objects get zeroed when copied from, affecting original object

[bvssvni]

rustc 1.0.0-nightly (6c065fc8c 2015-02-17) (built 2015-02-18)

From gfx-rs/gfx#574

In Gfx, something happens when *buffer (BufferHandle) is called, which zeroes whole or parts of the original object.

This might be a compiler bug.

cc @csherratt @kvark

[kvark]

Also see the workaround by @csherratt in PistonDevelopers/gfx_graphics#136

[kvark]

I managed to extract and simplify the case:

trait Resources {
    type Buffer: Copy;
}

struct BufferHandle<R: Resources> {
    raw: <R as Resources>::Buffer,
}
impl<R: Resources> Copy for BufferHandle<R> {}

#[derive(Copy)]
enum Res {}
impl Resources for Res {
    type Buffer = u32;
}

fn main() {
    let b: BufferHandle<Res> = BufferHandle { raw: 1 };
    let c = b;
    print!("{}{}", c.raw, b.raw);
}

Prints: 10

[alexcrichton]

cc @nikomatsakis, @pnkfelix, looks like an associated type bug. Thanks @kvark for the reduction!

Also nominating.

[nikomatsakis]

Will investigate.

[nikomatsakis]

And yes, thanks @kvark !

[dotdash]

https://github.com/rust-lang/rust/blob/master/src/librustc/middle/ty.rs#L3594 -- I guess if BoundCopy is present, that should remove TC::NeedsDrop?

[kvark]

I'm sorry, is there any progress on this one? We are considering switching everything to clone() (in gfx-rs) as a workaround, and that would be pretty inconvenient, not to mention the work wasted...

[bvssvni]

This is the only bug that blocks Piston at the moment, but it does across several projects. Is there a way I can help?

[brson]

@kvark @bvssvni No progress yet, but @pnkfelix and @nikomatsakis will solve it soon, I just know it!

[pnkfelix]

@kvark @bvssvni I have a plausible fix. I will hopefully put up a pull request with it tomorrow.