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]

5 files changed, 43 insertions, 0 deletions

diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index d43a7a66c5b..dc212e7cab3 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -231,6 +231,7 @@ use error::{FromError, Error};
 use fmt;
 use int;
 use iter::{Iterator, IteratorExt};
+use kinds::Copy;
 use mem::transmute;
 use ops::{BitOr, BitXor, BitAnd, Sub, Not};
 use option::Option;
@@ -420,6 +421,8 @@ pub enum IoErrorKind {
     NoProgress,
 }
 
+impl Copy for IoErrorKind {}
+
 /// A trait that lets you add a `detail` to an IoError easily
 trait UpdateIoError<T> {
     /// Returns an IoError with updated description and detail
@@ -1560,6 +1563,8 @@ pub enum SeekStyle {
     SeekCur,
 }
 
+impl Copy for SeekStyle {}
+
 /// An object implementing `Seek` internally has some form of cursor which can
 /// be moved within a stream of bytes. The stream typically has a fixed size,
 /// allowing seeking relative to either end.
@@ -1682,6 +1687,8 @@ pub enum FileMode {
     Truncate,
 }
 
+impl Copy for FileMode {}
+
 /// Access permissions with which the file should be opened. `File`s
 /// opened with `Read` will return an error if written to.
 pub enum FileAccess {
@@ -1693,6 +1700,8 @@ pub enum FileAccess {
     ReadWrite,
 }
 
+impl Copy for FileAccess {}
+
 /// Different kinds of files which can be identified by a call to stat
 #[deriving(PartialEq, Show, Hash, Clone)]
 pub enum FileType {
@@ -1715,6 +1724,8 @@ pub enum FileType {
     Unknown,
 }
 
+impl Copy for FileType {}
+
 /// A structure used to describe metadata information about a file. This
 /// structure is created through the `stat` method on a `Path`.
 ///
@@ -1766,6 +1777,8 @@ pub struct FileStat {
     pub unstable: UnstableFileStat,
 }
 
+impl Copy for FileStat {}
+
 /// This structure represents all of the possible information which can be
 /// returned from a `stat` syscall which is not contained in the `FileStat`
 /// structure. This information is not necessarily platform independent, and may
@@ -1795,6 +1808,8 @@ pub struct UnstableFileStat {
     pub gen: u64,
 }
 
+impl Copy for UnstableFileStat {}
+
 bitflags! {
     #[doc = "A set of permissions for a file or directory is represented"]
     #[doc = "by a set of flags which are or'd together."]
@@ -1889,6 +1904,8 @@ bitflags! {
     }
 }
 
+impl Copy for FilePermission {}
+
 impl Default for FilePermission {
     #[inline]
     fn default() -> FilePermission { FilePermission::empty() }
diff --git a/src/libstd/io/net/addrinfo.rs b/src/libstd/io/net/addrinfo.rs
index fea8372733c..fc81ab7b57a 100644
--- a/src/libstd/io/net/addrinfo.rs
+++ b/src/libstd/io/net/addrinfo.rs
@@ -22,6 +22,7 @@ pub use self::Protocol::*;
 use iter::IteratorExt;
 use io::{IoResult};
 use io::net::ip::{SocketAddr, IpAddr};
+use kinds::Copy;
 use option::Option;
 use option::Option::{Some, None};
 use sys;
@@ -32,6 +33,8 @@ pub enum SocketType {
     Stream, Datagram, Raw
 }
 
+impl Copy for SocketType {}
+
 /// Flags which can be or'd into the `flags` field of a `Hint`. These are used
 /// to manipulate how a query is performed.
 ///
@@ -46,12 +49,16 @@ pub enum Flag {
     V4Mapped,
 }
 
+impl Copy for Flag {}
+
 /// A transport protocol associated with either a hint or a return value of
 /// `lookup`
 pub enum Protocol {
     TCP, UDP
 }
 
+impl Copy for Protocol {}
+
 /// This structure is used to provide hints when fetching addresses for a
 /// remote host to control how the lookup is performed.
 ///
@@ -64,6 +71,8 @@ pub struct Hint {
     pub flags: uint,
 }
 
+impl Copy for Hint {}
+
 pub struct Info {
     pub address: SocketAddr,
     pub family: uint,
@@ -72,6 +81,8 @@ pub struct Info {
     pub flags: uint,
 }
 
+impl Copy for Info {}
+
 /// Easy name resolution. Given a hostname, returns the list of IP addresses for
 /// that hostname.
 pub fn get_host_addresses(host: &str) -> IoResult<Vec<IpAddr>> {
diff --git a/src/libstd/io/net/ip.rs b/src/libstd/io/net/ip.rs
index 3fa6f4a6091..f59dd37c0da 100644
--- a/src/libstd/io/net/ip.rs
+++ b/src/libstd/io/net/ip.rs
@@ -18,6 +18,7 @@
 pub use self::IpAddr::*;
 
 use fmt;
+use kinds::Copy;
 use io::{mod, IoResult, IoError};
 use io::net;
 use iter::{Iterator, IteratorExt};
@@ -36,6 +37,8 @@ pub enum IpAddr {
     Ipv6Addr(u16, u16, u16, u16, u16, u16, u16, u16)
 }
 
+impl Copy for IpAddr {}
+
 impl fmt::Show for IpAddr {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         match *self {
@@ -67,6 +70,8 @@ pub struct SocketAddr {
     pub port: Port,
 }
 
+impl Copy for SocketAddr {}
+
 impl fmt::Show for SocketAddr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.ip {
diff --git a/src/libstd/io/process.rs b/src/libstd/io/process.rs
index 61ebfb06c71..c46a6e82e44 100644
--- a/src/libstd/io/process.rs
+++ b/src/libstd/io/process.rs
@@ -480,6 +480,8 @@ pub enum StdioContainer {
     CreatePipe(bool /* readable */, bool /* writable */),
 }
 
+impl Copy for StdioContainer {}
+
 /// Describes the result of a process after it has terminated.
 /// Note that Windows have no signals, so the result is usually ExitStatus.
 #[deriving(PartialEq, Eq, Clone)]
@@ -491,6 +493,8 @@ pub enum ProcessExit {
     ExitSignal(int),
 }
 
+impl Copy for ProcessExit {}
+
 impl fmt::Show for ProcessExit {
     /// Format a ProcessExit enum, to nicely present the information.
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
diff --git a/src/libstd/io/util.rs b/src/libstd/io/util.rs
index e78bd1dd33f..faa52226a03 100644
--- a/src/libstd/io/util.rs
+++ b/src/libstd/io/util.rs
@@ -83,6 +83,8 @@ impl<R: Buffer> Buffer for LimitReader<R> {
 /// A `Writer` which ignores bytes written to it, like /dev/null.
 pub struct NullWriter;
 
+impl Copy for NullWriter {}
+
 impl Writer for NullWriter {
     #[inline]
     fn write(&mut self, _buf: &[u8]) -> io::IoResult<()> { Ok(()) }
@@ -91,6 +93,8 @@ impl Writer for NullWriter {
 /// A `Reader` which returns an infinite stream of 0 bytes, like /dev/zero.
 pub struct ZeroReader;
 
+impl Copy for ZeroReader {}
+
 impl Reader for ZeroReader {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
@@ -111,6 +115,8 @@ impl Buffer for ZeroReader {
 /// A `Reader` which is always at EOF, like /dev/null.
 pub struct NullReader;
 
+impl Copy for NullReader {}
+
 impl Reader for NullReader {
     #[inline]
     fn read(&mut self, _buf: &mut [u8]) -> io::IoResult<uint> {