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]

9 files changed, 27 insertions, 0 deletions

diff --git a/src/test/debuginfo/c-style-enum.rs b/src/test/debuginfo/c-style-enum.rs
index fec1d1b2789..b0a0142f6dd 100644
--- a/src/test/debuginfo/c-style-enum.rs
+++ b/src/test/debuginfo/c-style-enum.rs
@@ -104,18 +104,21 @@ use self::AutoDiscriminant::{One, Two, Three};
 use self::ManualDiscriminant::{OneHundred, OneThousand, OneMillion};
 use self::SingleVariant::TheOnlyVariant;
 
+#[deriving(Copy)]
 enum AutoDiscriminant {
     One,
     Two,
     Three
 }
 
+#[deriving(Copy)]
 enum ManualDiscriminant {
     OneHundred = 100,
     OneThousand = 1000,
     OneMillion = 1000000
 }
 
+#[deriving(Copy)]
 enum SingleVariant {
     TheOnlyVariant
 }
diff --git a/src/test/debuginfo/generic-method-on-generic-struct.rs b/src/test/debuginfo/generic-method-on-generic-struct.rs
index 7ceac0e7cea..4c0c82efea3 100644
--- a/src/test/debuginfo/generic-method-on-generic-struct.rs
+++ b/src/test/debuginfo/generic-method-on-generic-struct.rs
@@ -147,3 +147,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl<T:Copy> Copy for Struct<T> {}
+
diff --git a/src/test/debuginfo/method-on-enum.rs b/src/test/debuginfo/method-on-enum.rs
index d86aa54f451..8cb8fae75cf 100644
--- a/src/test/debuginfo/method-on-enum.rs
+++ b/src/test/debuginfo/method-on-enum.rs
@@ -148,3 +148,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl Copy for Enum {}
+
diff --git a/src/test/debuginfo/method-on-generic-struct.rs b/src/test/debuginfo/method-on-generic-struct.rs
index 2455c7aa519..d4244ee27d4 100644
--- a/src/test/debuginfo/method-on-generic-struct.rs
+++ b/src/test/debuginfo/method-on-generic-struct.rs
@@ -147,3 +147,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl<T:Copy> Copy for Struct<T> {}
+
diff --git a/src/test/debuginfo/method-on-struct.rs b/src/test/debuginfo/method-on-struct.rs
index 5e47d32e376..ca00587ba44 100644
--- a/src/test/debuginfo/method-on-struct.rs
+++ b/src/test/debuginfo/method-on-struct.rs
@@ -146,3 +146,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl Copy for Struct {}
+
diff --git a/src/test/debuginfo/method-on-trait.rs b/src/test/debuginfo/method-on-trait.rs
index 4d5f53fc120..e70f86a5367 100644
--- a/src/test/debuginfo/method-on-trait.rs
+++ b/src/test/debuginfo/method-on-trait.rs
@@ -152,3 +152,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl Copy for Struct {}
+
diff --git a/src/test/debuginfo/method-on-tuple-struct.rs b/src/test/debuginfo/method-on-tuple-struct.rs
index fb3bede37fd..31bdd20e409 100644
--- a/src/test/debuginfo/method-on-tuple-struct.rs
+++ b/src/test/debuginfo/method-on-tuple-struct.rs
@@ -144,3 +144,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl Copy for TupleStruct {}
+
diff --git a/src/test/debuginfo/self-in-default-method.rs b/src/test/debuginfo/self-in-default-method.rs
index 287813a959f..87fdb2c42c8 100644
--- a/src/test/debuginfo/self-in-default-method.rs
+++ b/src/test/debuginfo/self-in-default-method.rs
@@ -148,3 +148,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl Copy for Struct {}
+
diff --git a/src/test/debuginfo/self-in-generic-default-method.rs b/src/test/debuginfo/self-in-generic-default-method.rs
index bfb8abc9f66..6f488230521 100644
--- a/src/test/debuginfo/self-in-generic-default-method.rs
+++ b/src/test/debuginfo/self-in-generic-default-method.rs
@@ -149,3 +149,6 @@ fn main() {
 }
 
 fn zzz() {()}
+
+impl Copy for Struct {}
+