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]

3 files changed, 12 insertions, 0 deletions

diff --git a/src/libserialize/base64.rs b/src/libserialize/base64.rs
index c8ec1700a1d..dd5039c9b82 100644
--- a/src/libserialize/base64.rs
+++ b/src/libserialize/base64.rs
@@ -26,6 +26,8 @@ pub enum CharacterSet {
     UrlSafe
 }
 
+impl Copy for CharacterSet {}
+
 /// Contains configuration parameters for `to_base64`.
 pub struct Config {
     /// Character set to use
@@ -36,6 +38,8 @@ pub struct Config {
     pub line_length: Option<uint>
 }
 
+impl Copy for Config {}
+
 /// Configuration for RFC 4648 standard base64 encoding
 pub static STANDARD: Config =
     Config {char_set: Standard, pad: true, line_length: None};
@@ -168,6 +172,8 @@ pub enum FromBase64Error {
     InvalidBase64Length,
 }
 
+impl Copy for FromBase64Error {}
+
 impl fmt::Show for FromBase64Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
diff --git a/src/libserialize/hex.rs b/src/libserialize/hex.rs
index 4c20f72cac5..22392056ddf 100644
--- a/src/libserialize/hex.rs
+++ b/src/libserialize/hex.rs
@@ -68,6 +68,8 @@ pub enum FromHexError {
     InvalidHexLength,
 }
 
+impl Copy for FromHexError {}
+
 impl fmt::Show for FromHexError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
diff --git a/src/libserialize/json.rs b/src/libserialize/json.rs
index 248d78236ad..318c21234f5 100644
--- a/src/libserialize/json.rs
+++ b/src/libserialize/json.rs
@@ -247,6 +247,8 @@ pub enum ErrorCode {
     NotUtf8,
 }
 
+impl Copy for ErrorCode {}
+
 #[deriving(Clone, PartialEq, Show)]
 pub enum ParserError {
     /// msg, line, col
@@ -254,6 +256,8 @@ pub enum ParserError {
     IoError(io::IoErrorKind, &'static str),
 }
 
+impl Copy for ParserError {}
+
 // Builder and Parser have the same errors.
 pub type BuilderError = ParserError;