auto merge of #20514 : alexcrichton/rust/serialize-associated-type, r=aturon

This commit moves the libserialize crate (and will force the hand of the
rustc-serialize crate) to not require the `old_orphan_check` feature gate as
well as using associated types wherever possible. Concretely, the following
changes were made:

* The error type of `Encoder` and `Decoder` is now an associated type, meaning
  that these traits have no type parameters.

* The `Encoder` and `Decoder` type parameters on the `Encodable` and `Decodable`
  traits have moved to the corresponding method of the trait. This movement
  alleviates the dependency on `old_orphan_check` but implies that
  implementations can no longer be specialized for the type of encoder/decoder
  being implemented.

Due to the trait definitions changing, this is a:

[breaking-change]

7 files changed, 119 insertions, 52 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 03b9eaf76b9..c9d27e304ff 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -182,18 +182,34 @@ impl Name {
 /// A mark represents a unique id associated with a macro expansion
 pub type Mrk = u32;
 
+#[cfg(stage0)]
 impl<S: Encoder<E>, E> Encodable<S, E> for Ident {
     fn encode(&self, s: &mut S) -> Result<(), E> {
         s.emit_str(token::get_ident(*self).get())
     }
 }
 
+#[cfg(not(stage0))]
+impl Encodable for Ident {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_str(token::get_ident(*self).get())
+    }
+}
+
+#[cfg(stage0)]
 impl<D: Decoder<E>, E> Decodable<D, E> for Ident {
     fn decode(d: &mut D) -> Result<Ident, E> {
         Ok(str_to_ident(try!(d.read_str())[]))
     }
 }
 
+#[cfg(not(stage0))]
+impl Decodable for Ident {
+    fn decode<D: Decoder>(d: &mut D) -> Result<Ident, D::Error> {
+        Ok(str_to_ident(try!(d.read_str())[]))
+    }
+}
+
 /// Function name (not all functions have names)
 pub type FnIdent = Option<Ident>;
 
@@ -1686,27 +1702,7 @@ mod test {
     // are ASTs encodable?
     #[test]
     fn check_asts_encodable() {
-        use std::io;
-        let e = Crate {
-            module: Mod {
-                inner: Span {
-                    lo: BytePos(11),
-                    hi: BytePos(19),
-                    expn_id: NO_EXPANSION,
-                },
-                view_items: Vec::new(),
-                items: Vec::new(),
-            },
-            attrs: Vec::new(),
-            config: Vec::new(),
-            span: Span {
-                lo: BytePos(10),
-                hi: BytePos(20),
-                expn_id: NO_EXPANSION,
-            },
-            exported_macros: Vec::new(),
-        };
-        // doesn't matter which encoder we use....
-        let _f = &e as &serialize::Encodable<json::Encoder, fmt::Error>;
+        fn assert_encodable<T: serialize::Encodable>() {}
+        assert_encodable::<Crate>();
     }
 }
diff --git a/src/libsyntax/codemap.rs b/src/libsyntax/codemap.rs
index 2c7bbcb6faf..a49f2614cd7 100644
--- a/src/libsyntax/codemap.rs
+++ b/src/libsyntax/codemap.rs
@@ -120,6 +120,7 @@ impl PartialEq for Span {
 
 impl Eq for Span {}
 
+#[cfg(stage0)]
 impl<S:Encoder<E>, E> Encodable<S, E> for Span {
     /* Note #1972 -- spans are encoded but not decoded */
     fn encode(&self, s: &mut S) -> Result<(), E> {
@@ -127,12 +128,28 @@ impl<S:Encoder<E>, E> Encodable<S, E> for Span {
     }
 }
 
+#[cfg(not(stage0))]
+impl Encodable for Span {
+    /* Note #1972 -- spans are encoded but not decoded */
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_nil()
+    }
+}
+
+#[cfg(stage0)]
 impl<D:Decoder<E>, E> Decodable<D, E> for Span {
     fn decode(_d: &mut D) -> Result<Span, E> {
         Ok(DUMMY_SP)
     }
 }
 
+#[cfg(not(stage0))]
+impl Decodable for Span {
+    fn decode<D: Decoder>(_d: &mut D) -> Result<Span, D::Error> {
+        Ok(DUMMY_SP)
+    }
+}
+
 pub fn spanned<T>(lo: BytePos, hi: BytePos, t: T) -> Spanned<T> {
     respan(mk_sp(lo, hi), t)
 }
diff --git a/src/libsyntax/ext/deriving/decodable.rs b/src/libsyntax/ext/deriving/decodable.rs
index 882136cb862..c0631b8350b 100644
--- a/src/libsyntax/ext/deriving/decodable.rs
+++ b/src/libsyntax/ext/deriving/decodable.rs
@@ -52,27 +52,29 @@ fn expand_deriving_decodable_imp<F>(cx: &mut ExtCtxt,
     let trait_def = TraitDef {
         span: span,
         attributes: Vec::new(),
-        path: Path::new_(vec!(krate, "Decodable"), None,
-                         vec!(box Literal(Path::new_local("__D")),
-                              box Literal(Path::new_local("__E"))), true),
+        path: Path::new_(vec!(krate, "Decodable"), None, vec!(), true),
         additional_bounds: Vec::new(),
-        generics: LifetimeBounds {
-            lifetimes: Vec::new(),
-            bounds: vec!(("__D", vec!(Path::new_(
-                            vec!(krate, "Decoder"), None,
-                            vec!(box Literal(Path::new_local("__E"))), true))),
-                         ("__E", vec!()))
-        },
+        generics: LifetimeBounds::empty(),
         methods: vec!(
             MethodDef {
                 name: "decode",
-                generics: LifetimeBounds::empty(),
+                generics: LifetimeBounds {
+                    lifetimes: Vec::new(),
+                    bounds: vec!(("__D", vec!(Path::new_(
+                                    vec!(krate, "Decoder"), None,
+                                    vec!(), true))))
+                },
                 explicit_self: None,
                 args: vec!(Ptr(box Literal(Path::new_local("__D")),
                             Borrowed(None, MutMutable))),
-                ret_ty: Literal(Path::new_(vec!("std", "result", "Result"), None,
-                                          vec!(box Self,
-                                               box Literal(Path::new_local("__E"))), true)),
+                ret_ty: Literal(Path::new_(
+                    vec!("std", "result", "Result"),
+                    None,
+                    vec!(box Self, box Literal(Path::new_(
+                        vec!["__D", "Error"], None, vec![], false
+                    ))),
+                    true
+                )),
                 attributes: Vec::new(),
                 combine_substructure: combine_substructure(|a, b, c| {
                     decodable_substructure(a, b, c, krate)
diff --git a/src/libsyntax/ext/deriving/encodable.rs b/src/libsyntax/ext/deriving/encodable.rs
index b2c929123d5..4323d2979cc 100644
--- a/src/libsyntax/ext/deriving/encodable.rs
+++ b/src/libsyntax/ext/deriving/encodable.rs
@@ -128,29 +128,29 @@ fn expand_deriving_encodable_imp<F>(cx: &mut ExtCtxt,
     let trait_def = TraitDef {
         span: span,
         attributes: Vec::new(),
-        path: Path::new_(vec!(krate, "Encodable"), None,
-                         vec!(box Literal(Path::new_local("__S")),
-                              box Literal(Path::new_local("__E"))), true),
+        path: Path::new_(vec!(krate, "Encodable"), None, vec!(), true),
         additional_bounds: Vec::new(),
-        generics: LifetimeBounds {
-            lifetimes: Vec::new(),
-            bounds: vec!(("__S", vec!(Path::new_(
-                            vec!(krate, "Encoder"), None,
-                            vec!(box Literal(Path::new_local("__E"))), true))),
-                         ("__E", vec!()))
-        },
+        generics: LifetimeBounds::empty(),
         methods: vec!(
             MethodDef {
                 name: "encode",
-                generics: LifetimeBounds::empty(),
+                generics: LifetimeBounds {
+                    lifetimes: Vec::new(),
+                    bounds: vec!(("__S", vec!(Path::new_(
+                                    vec!(krate, "Encoder"), None,
+                                    vec!(), true))))
+                },
                 explicit_self: borrowed_explicit_self(),
                 args: vec!(Ptr(box Literal(Path::new_local("__S")),
                             Borrowed(None, MutMutable))),
-                ret_ty: Literal(Path::new_(vec!("std", "result", "Result"),
-                                           None,
-                                           vec!(box Tuple(Vec::new()),
-                                                box Literal(Path::new_local("__E"))),
-                                           true)),
+                ret_ty: Literal(Path::new_(
+                    vec!("std", "result", "Result"),
+                    None,
+                    vec!(box Tuple(Vec::new()), box Literal(Path::new_(
+                        vec!["__S", "Error"], None, vec![], false
+                    ))),
+                    true
+                )),
                 attributes: Vec::new(),
                 combine_substructure: combine_substructure(|a, b, c| {
                     encodable_substructure(a, b, c)
diff --git a/src/libsyntax/owned_slice.rs b/src/libsyntax/owned_slice.rs
index b87e2c6abbc..2a27431a086 100644
--- a/src/libsyntax/owned_slice.rs
+++ b/src/libsyntax/owned_slice.rs
@@ -82,12 +82,21 @@ impl<T> FromIterator<T> for OwnedSlice<T> {
     }
 }
 
+#[cfg(stage0)]
 impl<S: Encoder<E>, T: Encodable<S, E>, E> Encodable<S, E> for OwnedSlice<T> {
     fn encode(&self, s: &mut S) -> Result<(), E> {
        self.as_slice().encode(s)
     }
 }
 
+#[cfg(not(stage0))]
+impl<T: Encodable> Encodable for OwnedSlice<T> {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+       self.as_slice().encode(s)
+    }
+}
+
+#[cfg(stage0)]
 impl<D: Decoder<E>, T: Decodable<D, E>, E> Decodable<D, E> for OwnedSlice<T> {
     fn decode(d: &mut D) -> Result<OwnedSlice<T>, E> {
         Ok(OwnedSlice::from_vec(match Decodable::decode(d) {
@@ -96,3 +105,13 @@ impl<D: Decoder<E>, T: Decodable<D, E>, E> Decodable<D, E> for OwnedSlice<T> {
         }))
     }
 }
+
+#[cfg(not(stage0))]
+impl<T: Decodable> Decodable for OwnedSlice<T> {
+    fn decode<D: Decoder>(d: &mut D) -> Result<OwnedSlice<T>, D::Error> {
+        Ok(OwnedSlice::from_vec(match Decodable::decode(d) {
+            Ok(t) => t,
+            Err(e) => return Err(e)
+        }))
+    }
+}
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 4bfcc94a083..b7e89b32b70 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -653,6 +653,7 @@ impl<'a> PartialEq<InternedString > for &'a str {
     }
 }
 
+#[cfg(stage0)]
 impl<D:Decoder<E>, E> Decodable<D, E> for InternedString {
     fn decode(d: &mut D) -> Result<InternedString, E> {
         Ok(get_name(get_ident_interner().intern(
@@ -660,12 +661,28 @@ impl<D:Decoder<E>, E> Decodable<D, E> for InternedString {
     }
 }
 
+#[cfg(not(stage0))]
+impl Decodable for InternedString {
+    fn decode<D: Decoder>(d: &mut D) -> Result<InternedString, D::Error> {
+        Ok(get_name(get_ident_interner().intern(
+                    try!(d.read_str())[])))
+    }
+}
+
+#[cfg(stage0)]
 impl<S:Encoder<E>, E> Encodable<S, E> for InternedString {
     fn encode(&self, s: &mut S) -> Result<(), E> {
         s.emit_str(self.string[])
     }
 }
 
+#[cfg(not(stage0))]
+impl Encodable for InternedString {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_str(self.string[])
+    }
+}
+
 /// Returns the string contents of a name, using the task-local interner.
 #[inline]
 pub fn get_name(name: ast::Name) -> InternedString {
diff --git a/src/libsyntax/ptr.rs b/src/libsyntax/ptr.rs
index 6eee1d903ea..13eda7bb88f 100644
--- a/src/libsyntax/ptr.rs
+++ b/src/libsyntax/ptr.rs
@@ -111,14 +111,30 @@ impl<S, T: Hash<S>> Hash<S> for P<T> {
     }
 }
 
+#[cfg(stage0)]
 impl<E, D: Decoder<E>, T: 'static + Decodable<D, E>> Decodable<D, E> for P<T> {
     fn decode(d: &mut D) -> Result<P<T>, E> {
         Decodable::decode(d).map(P)
     }
 }
 
+#[cfg(not(stage0))]
+impl<T: 'static + Decodable> Decodable for P<T> {
+    fn decode<D: Decoder>(d: &mut D) -> Result<P<T>, D::Error> {
+        Decodable::decode(d).map(P)
+    }
+}
+
+#[cfg(stage0)]
 impl<E, S: Encoder<E>, T: Encodable<S, E>> Encodable<S, E> for P<T> {
     fn encode(&self, s: &mut S) -> Result<(), E> {
         (**self).encode(s)
     }
 }
+
+#[cfg(not(stage0))]
+impl<T: Encodable> Encodable for P<T> {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        (**self).encode(s)
+    }
+}