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 rust-lang#13231.

Part of RFC rust-lang#3.

[breaking-change]

Author: nikomatsakis

src/compiletest/common.rs

@@ -25,6 +25,8 @@ pub enum Mode {
     Codegen
 }
 
+impl Copy for Mode {}
+
 impl FromStr for Mode {
     fn from_str(s: &str) -> Option<Mode> {
         match s {

src/doc/guide-unsafe.md

@@ -661,6 +661,9 @@ extern {
     fn abort() -> !;
 }
 
+#[lang = "owned_box"]
+pub struct Box<T>(*mut T);
+
 #[lang="exchange_malloc"]
 unsafe fn allocate(size: uint, _align: uint) -> *mut u8 {
     let p = libc::malloc(size as libc::size_t) as *mut u8;

src/doc/reference.md

@@ -1660,6 +1660,7 @@ Implementations are defined with the keyword `impl`.
 
 ```
 # struct Point {x: f64, y: f64};
+# impl Copy for Point {}
 # type Surface = int;
 # struct BoundingBox {x: f64, y: f64, width: f64, height: f64};
 # trait Shape { fn draw(&self, Surface); fn bounding_box(&self) -> BoundingBox; }
@@ -1669,6 +1670,8 @@ struct Circle {
     center: Point,
 }
 
+impl Copy for Circle {}
+
 impl Shape for Circle {
     fn draw(&self, s: Surface) { do_draw_circle(s, *self); }
     fn bounding_box(&self) -> BoundingBox {
@@ -1791,6 +1794,7 @@ default visibility with the `priv` keyword. When an item is declared as `pub`,
 it can be thought of as being accessible to the outside world. For example:
 
 ```
+# #![allow(missing_copy_implementations)]
 # fn main() {}
 // Declare a private struct
 struct Foo;

src/libarena/lib.rs

@@ -466,7 +466,7 @@ impl<T> TypedArena<T> {
         }
 
         let ptr: &mut T = unsafe {
-            let ptr: &mut T = mem::transmute(self.ptr);
+            let ptr: &mut T = mem::transmute(self.ptr.clone());
             ptr::write(ptr, object);
             self.ptr.set(self.ptr.get().offset(1));
             ptr

src/libcollections/binary_heap.rs

@@ -35,6 +35,8 @@
 //!     position: uint
 //! }
 //!
+//! impl Copy for State {}
+//!
 //! // The priority queue depends on `Ord`.
 //! // Explicitly implement the trait so the queue becomes a min-heap
 //! // instead of a max-heap.

src/libcollections/dlist.rs

@@ -39,7 +39,12 @@ pub struct DList<T> {
 }
 
 type Link<T> = Option<Box<Node<T>>>;
-struct Rawlink<T> { p: *mut T }
+
+struct Rawlink<T> {
+    p: *mut T,
+}
+
+impl<T> Copy for Rawlink<T> {}
 
 struct Node<T> {
     next: Link<T>,
@@ -59,6 +64,8 @@ impl<'a, T> Clone for Items<'a, T> {
     fn clone(&self) -> Items<'a, T> { *self }
 }
 
+impl<'a,T> Copy for Items<'a,T> {}
+
 /// An iterator over mutable references to the items of a `DList`.
 pub struct MutItems<'a, T:'a> {
     list: &'a mut DList<T>,

src/libcollections/enum_set.rs

@@ -27,6 +27,8 @@ pub struct EnumSet<E> {
     bits: uint
 }
 
+impl<E> Copy for EnumSet<E> {}
+
 impl<E:CLike+fmt::Show> fmt::Show for EnumSet<E> {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         try!(write!(fmt, "{{"));
@@ -269,6 +271,8 @@ mod test {
         A, B, C
     }
 
+    impl Copy for Foo {}
+
     impl CLike for Foo {
         fn to_uint(&self) -> uint {
             *self as uint
@@ -477,6 +481,9 @@ mod test {
             V50, V51, V52, V53, V54, V55, V56, V57, V58, V59,
             V60, V61, V62, V63, V64, V65, V66, V67, V68, V69,
         }
+
+        impl Copy for Bar {}
+
         impl CLike for Bar {
             fn to_uint(&self) -> uint {
                 *self as uint

src/libcollections/hash/sip.rs

@@ -43,6 +43,8 @@ pub struct SipState {
     ntail: uint,  // how many bytes in tail are valid
 }
 
+impl Copy for SipState {}
+
 // sadly, these macro definitions can't appear later,
 // because they're needed in the following defs;
 // this design could be improved.
@@ -211,6 +213,7 @@ impl Default for SipState {
 
 /// `SipHasher` computes the SipHash algorithm from a stream of bytes.
 #[deriving(Clone)]
+#[allow(missing_copy_implementations)]
 pub struct SipHasher {
     k0: u64,
     k1: u64,

src/libcollections/slice.rs

@@ -91,7 +91,7 @@ use self::Direction::*;
 use alloc::boxed::Box;
 use core::borrow::{BorrowFrom, BorrowFromMut, ToOwned};
 use core::cmp;
-use core::kinds::Sized;
+use core::kinds::{Copy, Sized};
 use core::mem::size_of;
 use core::mem;
 use core::prelude::{Clone, Greater, Iterator, IteratorExt, Less, None, Option};
@@ -177,12 +177,16 @@ impl ElementSwaps {
 
 enum Direction { Pos, Neg }
 
+impl Copy for Direction {}
+
 /// An `Index` and `Direction` together.
 struct SizeDirection {
     size: uint,
     dir: Direction,
 }
 
+impl Copy for SizeDirection {}
+
 impl Iterator<(uint, uint)> for ElementSwaps {
     #[inline]
     fn next(&mut self) -> Option<(uint, uint)> {
@@ -1482,11 +1486,17 @@ mod tests {
             fn clone(&self) -> S {
                 self.f.set(self.f.get() + 1);
                 if self.f.get() == 10 { panic!() }
-                S { f: self.f, boxes: self.boxes.clone() }
+                S {
+                    f: self.f.clone(),
+                    boxes: self.boxes.clone(),
+                }
             }
         }
 
-        let s = S { f: Cell::new(0), boxes: (box 0, Rc::new(0)) };
+        let s = S {
+            f: Cell::new(0),
+            boxes: (box 0, Rc::new(0)),
+        };
         let _ = Vec::from_elem(100, s);
     }
 

src/libcollections/str.rs

@@ -228,24 +228,32 @@ impl<'a> Iterator<char> for Decompositions<'a> {
             _ => self.sorted = false
         }
 
-        let decomposer = match self.kind {
-            Canonical => unicode::char::decompose_canonical,
-            Compatible => unicode::char::decompose_compatible
-        };
-
         if !self.sorted {
             for ch in self.iter {
                 let buffer = &mut self.buffer;
                 let sorted = &mut self.sorted;
-                decomposer(ch, |d| {
-                    let class = unicode::char::canonical_combining_class(d);
-                    if class == 0 && !*sorted {
-                        canonical_sort(buffer.as_mut_slice());
-                        *sorted = true;
+                {
+                    let callback = |d| {
+                        let class =
+                            unicode::char::canonical_combining_class(d);
+                        if class == 0 && !*sorted {
+                            canonical_sort(buffer.as_mut_slice());
+                            *sorted = true;
+                        }
+                        buffer.push((d, class));
+                    };
+                    match self.kind {
+                        Canonical => {
+                            unicode::char::decompose_canonical(ch, callback)
+                        }
+                        Compatible => {
+                            unicode::char::decompose_compatible(ch, callback)
+                        }
                     }
-                    buffer.push((d, class));
-                });
-                if *sorted { break }
+                }
+                if *sorted {
+                    break
+                }
             }
         }
 

src/libcore/atomic.rs

@@ -17,6 +17,7 @@ pub use self::Ordering::*;
 use intrinsics;
 use std::kinds::marker;
 use cell::UnsafeCell;
+use kinds::Copy;
 
 /// A boolean type which can be safely shared between threads.
 #[stable]
@@ -81,6 +82,8 @@ pub enum Ordering {
     SeqCst,
 }
 
+impl Copy for Ordering {}
+
 /// An `AtomicBool` initialized to `false`.
 #[unstable = "may be renamed, pending conventions for static initalizers"]
 pub const INIT_ATOMIC_BOOL: AtomicBool =

src/libcore/char.rs

@@ -519,3 +519,4 @@ impl Iterator<char> for DefaultEscapedChars {
         }
     }
 }
+

src/libcore/cmp.rs

@@ -43,9 +43,8 @@
 
 pub use self::Ordering::*;
 
-use kinds::Sized;
-use option::Option;
-use option::Option::{Some, None};
+use kinds::{Copy, Sized};
+use option::{Option, Some, None};
 
 /// Trait for values that can be compared for equality and inequality.
 ///
@@ -106,6 +105,8 @@ pub enum Ordering {
    Greater = 1i,
 }
 
+impl Copy for Ordering {}
+
 impl Ordering {
     /// Reverse the `Ordering`, so that `Less` becomes `Greater` and
     /// vice versa.

src/libcore/fmt/mod.rs

@@ -46,6 +46,8 @@ pub type Result = result::Result<(), Error>;
 #[experimental = "core and I/O reconciliation may alter this definition"]
 pub struct Error;
 
+impl Copy for Error {}
+
 /// A collection of methods that are required to format a message into a stream.
 ///
 /// This trait is the type which this modules requires when formatting
@@ -135,6 +137,8 @@ impl<'a> Argument<'a> {
     }
 }
 
+impl<'a> Copy for Argument<'a> {}
+
 impl<'a> Arguments<'a> {
     /// When using the format_args!() macro, this function is used to generate the
     /// Arguments structure.

src/libcore/fmt/num.rs

@@ -16,6 +16,7 @@
 
 use fmt;
 use iter::DoubleEndedIteratorExt;
+use kinds::Copy;
 use num::{Int, cast};
 use slice::SlicePrelude;
 
@@ -114,6 +115,8 @@ pub struct Radix {
     base: u8,
 }
 
+impl Copy for Radix {}
+
 impl Radix {
     fn new(base: u8) -> Radix {
         assert!(2 <= base && base <= 36, "the base must be in the range of 2..36: {}", base);
@@ -136,6 +139,8 @@ impl GenericRadix for Radix {
 #[unstable = "may be renamed or move to a different module"]
 pub struct RadixFmt<T, R>(T, R);
 
+impl<T,R> Copy for RadixFmt<T,R> where T: Copy, R: Copy {}
+
 /// Constructs a radix formatter in the range of `2..36`.
 ///
 /// # Example

src/libcore/fmt/rt.rs

@@ -20,13 +20,16 @@ pub use self::Alignment::*;
 pub use self::Count::*;
 pub use self::Position::*;
 pub use self::Flag::*;
+use kinds::Copy;
 
 #[doc(hidden)]
 pub struct Argument<'a> {
     pub position: Position,
     pub format: FormatSpec,
 }
 
+impl<'a> Copy for Argument<'a> {}
+
 #[doc(hidden)]
 pub struct FormatSpec {
     pub fill: char,
@@ -36,6 +39,8 @@ pub struct FormatSpec {
     pub width: Count,
 }
 
+impl Copy for FormatSpec {}
+
 /// Possible alignments that can be requested as part of a formatting directive.
 #[deriving(PartialEq)]
 pub enum Alignment {
@@ -49,16 +54,22 @@ pub enum Alignment {
     AlignUnknown,
 }
 
+impl Copy for Alignment {}
+
 #[doc(hidden)]
 pub enum Count {
     CountIs(uint), CountIsParam(uint), CountIsNextParam, CountImplied,
 }
 
+impl Copy for Count {}
+
 #[doc(hidden)]
 pub enum Position {
     ArgumentNext, ArgumentIs(uint)
 }
 
+impl Copy for Position {}
+
 /// Flags which can be passed to formatting via a directive.
 ///
 /// These flags are discovered through the `flags` field of the `Formatter`
@@ -78,3 +89,5 @@ pub enum Flag {
     /// being aware of the sign to be printed.
     FlagSignAwareZeroPad,
 }
+
+impl Copy for Flag {}

src/libcore/intrinsics.rs

@@ -42,6 +42,8 @@
 #![experimental]
 #![allow(missing_docs)]
 
+use kinds::Copy;
+
 pub type GlueFn = extern "Rust" fn(*const i8);
 
 #[lang="ty_desc"]
@@ -59,6 +61,8 @@ pub struct TyDesc {
     pub name: &'static str,
 }
 
+impl Copy for TyDesc {}
+
 extern "rust-intrinsic" {
 
     // NB: These intrinsics take unsafe pointers because they mutate aliased
@@ -539,6 +543,8 @@ pub struct TypeId {
     t: u64,
 }
 
+impl Copy for TypeId {}
+
 impl TypeId {
     /// Returns the `TypeId` of the type this generic function has been instantiated with
     pub fn of<T: 'static>() -> TypeId {