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]

1 files changed, 3 insertions, 0 deletions

diff --git a/src/libterm/lib.rs b/src/libterm/lib.rs
index 0e4ecb8f73e..575ec860f97 100644
--- a/src/libterm/lib.rs
+++ b/src/libterm/lib.rs
@@ -165,6 +165,7 @@ pub mod color {
 /// Terminal attributes
 pub mod attr {
     pub use self::Attr::*;
+    use std::kinds::Copy;
 
     /// Terminal attributes for use with term.attr().
     ///
@@ -193,6 +194,8 @@ pub mod attr {
         /// Convenience attribute to set the background color
         BackgroundColor(super::color::Color)
     }
+
+    impl Copy for Attr {}
 }
 
 /// A terminal with similar capabilities to an ANSI Terminal