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]

4 files changed, 20 insertions, 0 deletions

diff --git a/src/libsyntax/parse/lexer/comments.rs b/src/libsyntax/parse/lexer/comments.rs
index aeec6ee13fd..a17d66476c0 100644
--- a/src/libsyntax/parse/lexer/comments.rs
+++ b/src/libsyntax/parse/lexer/comments.rs
@@ -36,6 +36,8 @@ pub enum CommentStyle {
     BlankLine,
 }
 
+impl Copy for CommentStyle {}
+
 #[deriving(Clone)]
 pub struct Comment {
     pub style: CommentStyle,
diff --git a/src/libsyntax/parse/obsolete.rs b/src/libsyntax/parse/obsolete.rs
index 650f8295d01..2a2bb42cef0 100644
--- a/src/libsyntax/parse/obsolete.rs
+++ b/src/libsyntax/parse/obsolete.rs
@@ -34,6 +34,8 @@ pub enum ObsoleteSyntax {
     ObsoleteExternCrateRenaming,
 }
 
+impl Copy for ObsoleteSyntax {}
+
 pub trait ParserObsoleteMethods {
     /// Reports an obsolete syntax non-fatal error.
     fn obsolete(&mut self, sp: Span, kind: ObsoleteSyntax);
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index bb3d28ce2bb..4929ee885ac 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -98,6 +98,8 @@ bitflags! {
     }
 }
 
+impl Copy for Restrictions {}
+
 type ItemInfo = (Ident, Item_, Option<Vec<Attribute> >);
 
 /// How to parse a path. There are four different kinds of paths, all of which
@@ -114,6 +116,8 @@ pub enum PathParsingMode {
     LifetimeAndTypesWithColons,
 }
 
+impl Copy for PathParsingMode {}
+
 enum ItemOrViewItem {
     /// Indicates a failure to parse any kind of item. The attributes are
     /// returned.
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 52b54bc7f2d..4b1e9482a7d 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -42,6 +42,8 @@ pub enum BinOpToken {
     Shr,
 }
 
+impl Copy for BinOpToken {}
+
 /// A delimeter token
 #[deriving(Clone, Encodable, Decodable, PartialEq, Eq, Hash, Show)]
 pub enum DelimToken {
@@ -53,6 +55,8 @@ pub enum DelimToken {
     Brace,
 }
 
+impl Copy for DelimToken {}
+
 #[deriving(Clone, Encodable, Decodable, PartialEq, Eq, Hash, Show)]
 pub enum IdentStyle {
     /// `::` follows the identifier with no whitespace in-between.
@@ -85,6 +89,12 @@ impl Lit {
     }
 }
 
+#[cfg(not(stage0))]
+impl Copy for Lit {}
+
+#[cfg(not(stage0))]
+impl Copy for IdentStyle {}
+
 #[allow(non_camel_case_types)]
 #[deriving(Clone, Encodable, Decodable, PartialEq, Eq, Hash, Show)]
 pub enum Token {
@@ -435,6 +445,8 @@ macro_rules! declare_special_idents_and_keywords {(
             $( $rk_variant, )*
         }
 
+        impl Copy for Keyword {}
+
         impl Keyword {
             pub fn to_name(&self) -> ast::Name {
                 match *self {