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.

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]

Author: pcwalton

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

@@ -518,3 +518,4 @@ impl Iterator<char> for DefaultEscapedChars {
         }
     }
 }
+

src/libcore/cmp.rs

@@ -43,7 +43,7 @@
 
 pub use self::Ordering::*;
 
-use kinds::Sized;
+use kinds::{Copy, Sized};
 use option::{Option, Some, None};
 
 /// Trait for values that can be compared for equality and inequality.
@@ -105,6 +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

@@ -44,6 +44,8 @@ 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
@@ -102,6 +104,8 @@ pub struct Argument<'a> {
     value: &'a Void,
 }
 
+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. The compiler inserts an `unsafe` block to call this,

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 {