From 096a28607fb80c91e6e2ca64d9ef44c4e550e96c Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Fri, 5 Dec 2014 17:01:33 -0800
Subject: librustc: Make `Copy` opt-in.

This change makes the compiler no longer infer whether types (structures
and enumerations) implement the `Copy` trait (and thus are implicitly
copyable). Rather, you must implement `Copy` yourself via `impl Copy for
MyType {}`.

A new warning has been added, `missing_copy_implementations`, to warn
you if a non-generic public type has been added that could have
implemented `Copy` but didn't.

For convenience, you may *temporarily* opt out of this behavior by using
`#![feature(opt_out_copy)]`. Note though that this feature gate will never be
accepted and will be removed by the time that 1.0 is released, so you should
transition your code away from using it.

This breaks code like:

    #[deriving(Show)]
    struct Point2D {
        x: int,
        y: int,
    }

    fn main() {
        let mypoint = Point2D {
            x: 1,
            y: 1,
        };
        let otherpoint = mypoint;
        println!("{}{}", mypoint, otherpoint);
    }

Change this code to:

    #[deriving(Show)]
    struct Point2D {
        x: int,
        y: int,
    }

    impl Copy for Point2D {}

    fn main() {
        let mypoint = Point2D {
            x: 1,
            y: 1,
        };
        let otherpoint = mypoint;
        println!("{}{}", mypoint, otherpoint);
    }

This is the backwards-incompatible part of #13231.

Part of RFC #3.

[breaking-change]
---
 src/doc/guide-unsafe.md | 3 +++
 src/doc/reference.md    | 4 ++++
 2 files changed, 7 insertions(+)

(limited to 'src/doc')

diff --git a/src/doc/guide-unsafe.md b/src/doc/guide-unsafe.md
index 5b248126c80..bda1b345632 100644
--- a/src/doc/guide-unsafe.md
+++ b/src/doc/guide-unsafe.md
@@ -661,6 +661,9 @@ extern {
     fn abort() -> !;
 }
 
+#[lang = "owned_box"]
+pub struct Box<T>(*mut T);
+
 #[lang="exchange_malloc"]
 unsafe fn allocate(size: uint, _align: uint) -> *mut u8 {
     let p = libc::malloc(size as libc::size_t) as *mut u8;
diff --git a/src/doc/reference.md b/src/doc/reference.md
index 9ac4469d549..f6ee5cadbc6 100644
--- a/src/doc/reference.md
+++ b/src/doc/reference.md
@@ -1660,6 +1660,7 @@ Implementations are defined with the keyword `impl`.
 
 ```
 # struct Point {x: f64, y: f64};
+# impl Copy for Point {}
 # type Surface = int;
 # struct BoundingBox {x: f64, y: f64, width: f64, height: f64};
 # trait Shape { fn draw(&self, Surface); fn bounding_box(&self) -> BoundingBox; }
@@ -1669,6 +1670,8 @@ struct Circle {
     center: Point,
 }
 
+impl Copy for Circle {}
+
 impl Shape for Circle {
     fn draw(&self, s: Surface) { do_draw_circle(s, *self); }
     fn bounding_box(&self) -> BoundingBox {
@@ -1791,6 +1794,7 @@ default visibility with the `priv` keyword. When an item is declared as `pub`,
 it can be thought of as being accessible to the outside world. For example:
 
 ```
+# #![allow(missing_copy_implementations)]
 # fn main() {}
 // Declare a private struct
 struct Foo;
-- 
cgit 1.4.1-3-g733a5