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, 18 insertions, 0 deletions

diff --git a/src/librustc_trans/trans/cleanup.rs b/src/librustc_trans/trans/cleanup.rs
index 33393ba76c5..ba3e70fe036 100644
--- a/src/librustc_trans/trans/cleanup.rs
+++ b/src/librustc_trans/trans/cleanup.rs
@@ -55,6 +55,8 @@ pub struct CustomScopeIndex {
     index: uint
 }
 
+impl Copy for CustomScopeIndex {}
+
 pub const EXIT_BREAK: uint = 0;
 pub const EXIT_LOOP: uint = 1;
 pub const EXIT_MAX: uint = 2;
@@ -88,11 +90,15 @@ pub enum EarlyExitLabel {
     LoopExit(ast::NodeId, uint)
 }
 
+impl Copy for EarlyExitLabel {}
+
 pub struct CachedEarlyExit {
     label: EarlyExitLabel,
     cleanup_block: BasicBlockRef,
 }
 
+impl Copy for CachedEarlyExit {}
+
 pub trait Cleanup<'tcx> {
     fn must_unwind(&self) -> bool;
     fn clean_on_unwind(&self) -> bool;
@@ -111,6 +117,8 @@ pub enum ScopeId {
     CustomScope(CustomScopeIndex)
 }
 
+impl Copy for ScopeId {}
+
 impl<'blk, 'tcx> CleanupMethods<'blk, 'tcx> for FunctionContext<'blk, 'tcx> {
     /// Invoked when we start to trans the code contained within a new cleanup scope.
     fn push_ast_cleanup_scope(&self, debug_loc: NodeInfo) {
@@ -876,6 +884,8 @@ pub struct DropValue<'tcx> {
     zero: bool
 }
 
+impl<'tcx> Copy for DropValue<'tcx> {}
+
 impl<'tcx> Cleanup<'tcx> for DropValue<'tcx> {
     fn must_unwind(&self) -> bool {
         self.must_unwind
@@ -910,12 +920,16 @@ pub enum Heap {
     HeapExchange
 }
 
+impl Copy for Heap {}
+
 pub struct FreeValue<'tcx> {
     ptr: ValueRef,
     heap: Heap,
     content_ty: Ty<'tcx>
 }
 
+impl<'tcx> Copy for FreeValue<'tcx> {}
+
 impl<'tcx> Cleanup<'tcx> for FreeValue<'tcx> {
     fn must_unwind(&self) -> bool {
         true
@@ -950,6 +964,8 @@ pub struct FreeSlice {
     heap: Heap,
 }
 
+impl Copy for FreeSlice {}
+
 impl<'tcx> Cleanup<'tcx> for FreeSlice {
     fn must_unwind(&self) -> bool {
         true
@@ -981,6 +997,8 @@ pub struct LifetimeEnd {
     ptr: ValueRef,
 }
 
+impl Copy for LifetimeEnd {}
+
 impl<'tcx> Cleanup<'tcx> for LifetimeEnd {
     fn must_unwind(&self) -> bool {
         false