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, 20 insertions, 2 deletions

diff --git a/src/libsyntax/abi.rs b/src/libsyntax/abi.rs
index 87693f39bbd..71d29bca401 100644
--- a/src/libsyntax/abi.rs
+++ b/src/libsyntax/abi.rs
@@ -16,8 +16,17 @@ pub use self::AbiArchitecture::*;
 use std::fmt;
 
 #[deriving(PartialEq)]
-pub enum Os { OsWindows, OsMacos, OsLinux, OsAndroid, OsFreebsd, OsiOS,
-              OsDragonfly }
+pub enum Os {
+    OsWindows,
+    OsMacos,
+    OsLinux,
+    OsAndroid,
+    OsFreebsd,
+    OsiOS,
+    OsDragonfly,
+}
+
+impl Copy for Os {}
 
 #[deriving(PartialEq, Eq, Hash, Encodable, Decodable, Clone)]
 pub enum Abi {
@@ -39,6 +48,8 @@ pub enum Abi {
     RustCall,
 }
 
+impl Copy for Abi {}
+
 #[allow(non_camel_case_types)]
 #[deriving(PartialEq)]
 pub enum Architecture {
@@ -49,6 +60,8 @@ pub enum Architecture {
     Mipsel
 }
 
+impl Copy for Architecture {}
+
 pub struct AbiData {
     abi: Abi,
 
@@ -56,6 +69,8 @@ pub struct AbiData {
     name: &'static str,
 }
 
+impl Copy for AbiData {}
+
 pub enum AbiArchitecture {
     /// Not a real ABI (e.g., intrinsic)
     RustArch,
@@ -66,6 +81,9 @@ pub enum AbiArchitecture {
 }
 
 #[allow(non_upper_case_globals)]
+impl Copy for AbiArchitecture {}
+
+#[allow(non_upper_case_globals)]
 static AbiDatas: &'static [AbiData] = &[
     // Platform-specific ABIs
     AbiData {abi: Cdecl, name: "cdecl" },