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dropck: Remove Copy from special-cased traits #24906

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Merged
merged 2 commits into from
Apr 28, 2015

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pnkfelix
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dropck: Remove Copy from special-cased traits

Fix #24895.

[breaking-change]

What does this break? Basically, code that implements Drop and is
using T:Copy for one of its type parameters and is relying on the
Drop Check rule not applying to it.

Here is an example:

#![allow(dead_code,unused_variables,unused_assignments)]
struct D<T:Copy>(T);
impl<T:Copy> Drop for D<T> { fn drop(&mut self) { } }

trait UserT { fn c(&self) { } }
impl<T:Copy> UserT for T { }
struct E<T:UserT>(T);
impl<T:UserT> Drop for E<T> { fn drop(&mut self) { } }

// This one will start breaking.
fn foo() { let (d2, d1); d1 = D(34); d2 = D(&d1); }

#[cfg(this_one_does_and_should_always_break)]
fn bar() { let (e2, e1); e1 = E(34); e2 = E(&e1); }

fn main() {
    foo();
}

[breaking-change]

What does this break?  Basically, code that implements `Drop` and is
using `T:Copy` for one of its type parameters and is relying on the
Drop Check rule not applying to it.

Here is an example:

```rust
#![allow(dead_code,unused_variables,unused_assignments)]
struct D<T:Copy>(T);
impl<T:Copy> Drop for D<T> { fn drop(&mut self) { } }

trait UserT { fn c(&self) { } }
impl<T:Copy> UserT for T { }
struct E<T:UserT>(T);
impl<T:UserT> Drop for E<T> { fn drop(&mut self) { } }

// This one will start breaking.
fn foo() { let (d2, d1); d1 = D(34); d2 = D(&d1); }

#[cfg(this_one_does_and_should_always_break)]
fn bar() { let (e2, e1); e1 = E(34); e2 = E(&e1); }

fn main() {
    foo();
}
```
@rust-highfive
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r? @nikomatsakis

(rust_highfive has picked a reviewer for you, use r? to override)

@alexcrichton
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@bors: r+ 1f79348 p=100

Oh dear! Also nominating for beta-cherry-pick

@alexcrichton alexcrichton added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Apr 28, 2015
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bors commented Apr 28, 2015

⌛ Testing commit 1f79348 with merge 441b3f0...

bors added a commit that referenced this pull request Apr 28, 2015
dropck: Remove `Copy` from special-cased traits

Fix #24895.

[breaking-change]

What does this break?  Basically, code that implements `Drop` and is
using `T:Copy` for one of its type parameters and is relying on the
Drop Check rule not applying to it.

Here is an example:

```rust
#![allow(dead_code,unused_variables,unused_assignments)]
struct D<T:Copy>(T);
impl<T:Copy> Drop for D<T> { fn drop(&mut self) { } }

trait UserT { fn c(&self) { } }
impl<T:Copy> UserT for T { }
struct E<T:UserT>(T);
impl<T:UserT> Drop for E<T> { fn drop(&mut self) { } }

// This one will start breaking.
fn foo() { let (d2, d1); d1 = D(34); d2 = D(&d1); }

#[cfg(this_one_does_and_should_always_break)]
fn bar() { let (e2, e1); e1 = E(34); e2 = E(&e1); }

fn main() {
    foo();
}
```
@bors bors merged commit 1f79348 into rust-lang:master Apr 28, 2015
@pnkfelix
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accepted for backport to beta channel.

@pnkfelix pnkfelix added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Apr 30, 2015
@brson brson removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Apr 30, 2015
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brson commented Apr 30, 2015

Backported.

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Copy: Clone has made dropck implementation unsound!
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