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, 10 insertions, 0 deletions

diff --git a/src/libsyntax/diagnostic.rs b/src/libsyntax/diagnostic.rs
index 293c1b3a953..bbda80bd96c 100644
--- a/src/libsyntax/diagnostic.rs
+++ b/src/libsyntax/diagnostic.rs
@@ -40,6 +40,8 @@ pub enum RenderSpan {
     FileLine(Span),
 }
 
+impl Copy for RenderSpan {}
+
 impl RenderSpan {
     fn span(self) -> Span {
         match self {
@@ -61,6 +63,8 @@ pub enum ColorConfig {
     Never
 }
 
+impl Copy for ColorConfig {}
+
 pub trait Emitter {
     fn emit(&mut self, cmsp: Option<(&codemap::CodeMap, Span)>,
             msg: &str, code: Option<&str>, lvl: Level);
@@ -73,10 +77,14 @@ pub trait Emitter {
 /// how a rustc task died (if so desired).
 pub struct FatalError;
 
+impl Copy for FatalError {}
+
 /// Signifies that the compiler died with an explicit call to `.bug`
 /// or `.span_bug` rather than a failed assertion, etc.
 pub struct ExplicitBug;
 
+impl Copy for ExplicitBug {}
+
 /// A span-handler is like a handler but also
 /// accepts span information for source-location
 /// reporting.
@@ -230,6 +238,8 @@ pub enum Level {
     Help,
 }
 
+impl Copy for Level {}
+
 impl fmt::Show for Level {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         use std::fmt::Show;