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, 9 insertions, 2 deletions

diff --git a/src/libcore/iter.rs b/src/libcore/iter.rs
index 49865bd3c7d..ddca9d36bed 100644
--- a/src/libcore/iter.rs
+++ b/src/libcore/iter.rs
@@ -59,6 +59,7 @@ pub use self::MinMaxResult::*;
 use clone::Clone;
 use cmp;
 use cmp::Ord;
+use kinds::Copy;
 use mem;
 use num::{ToPrimitive, Int};
 use ops::{Add, Deref};
@@ -1166,7 +1167,8 @@ pub struct Cycle<T> {
     iter: T,
 }
 
-#[unstable = "trait is unstable"]
+impl<T:Copy> Copy for Cycle<T> {}
+
 impl<A, T: Clone + Iterator<A>> Iterator<A> for Cycle<T> {
     #[inline]
     fn next(&mut self) -> Option<A> {
@@ -1576,7 +1578,8 @@ pub struct Peekable<A, T> {
     peeked: Option<A>,
 }
 
-#[unstable = "trait is unstable"]
+impl<T:Copy,A:Copy> Copy for Peekable<A,T> {}
+
 impl<A, T: Iterator<A>> Iterator<A> for Peekable<A, T> {
     #[inline]
     fn next(&mut self) -> Option<A> {
@@ -2115,6 +2118,8 @@ pub struct Counter<A> {
     step: A,
 }
 
+impl<A:Copy> Copy for Counter<A> {}
+
 /// Creates a new counter with the specified start/step
 #[inline]
 #[unstable = "may be renamed"]
@@ -2146,6 +2151,8 @@ pub struct Range<A> {
     one: A,
 }
 
+impl<A:Copy> Copy for Range<A> {}
+
 /// Returns an iterator over the given range [start, stop) (that is, starting
 /// at start (inclusive), and ending at stop (exclusive)).
 ///