Move return type an associated type of the Fn* traits. Mostly this involves tweaking things in

the compiler that assumed two input types to assume two ouputs; we also have to teach `project.rs`
to project `Output` from the unboxed closure and fn traits.

Author: nikomatsakis

src/libcollections/btree/set.rs

@@ -758,7 +758,9 @@ mod test {
         expected: &'b [int],
     }
 
-    impl<'a, 'b, 'c> FnMut(&'c int) -> bool for Counter<'a, 'b> {
+    impl<'a, 'b, 'c> FnMut<(&'c int,)> for Counter<'a, 'b> {
+        type Output = bool;
+
         extern "rust-call" fn call_mut(&mut self, (&x,): (&'c int,)) -> bool {
             assert_eq!(x, self.expected[*self.i]);
             *self.i += 1;

src/libcore/ops.rs

@@ -1117,29 +1117,33 @@ impl<'a, T: ?Sized> DerefMut for &'a mut T {
 #[lang="fn"]
 #[unstable(feature = "core",
            reason = "uncertain about variadic generics, input versus associated types")]
-pub trait Fn<Args,Result> {
+#[cfg(stage0)]
+pub trait Fn<Args,Output> {
     /// This is called when the call operator is used.
-    extern "rust-call" fn call(&self, args: Args) -> Result;
+    extern "rust-call" fn call(&self, args: Args) -> Output;
 }
 
 /// A version of the call operator that takes a mutable receiver.
 #[lang="fn_mut"]
 #[unstable(feature = "core",
            reason = "uncertain about variadic generics, input versus associated types")]
-pub trait FnMut<Args,Result> {
+#[cfg(stage0)]
+pub trait FnMut<Args,Output> {
     /// This is called when the call operator is used.
-    extern "rust-call" fn call_mut(&mut self, args: Args) -> Result;
+    extern "rust-call" fn call_mut(&mut self, args: Args) -> Output;
 }
 
 /// A version of the call operator that takes a by-value receiver.
 #[lang="fn_once"]
 #[unstable(feature = "core",
            reason = "uncertain about variadic generics, input versus associated types")]
-pub trait FnOnce<Args,Result> {
+#[cfg(stage0)]
+pub trait FnOnce<Args,Output> {
     /// This is called when the call operator is used.
-    extern "rust-call" fn call_once(self, args: Args) -> Result;
+    extern "rust-call" fn call_once(self, args: Args) -> Output;
 }
 
+#[cfg(stage0)]
 impl<F: ?Sized, A, R> FnMut<A, R> for F
     where F : Fn<A, R>
 {
@@ -1148,10 +1152,69 @@ impl<F: ?Sized, A, R> FnMut<A, R> for F
     }
 }
 
+#[cfg(stage0)]
 impl<F,A,R> FnOnce<A,R> for F
     where F : FnMut<A,R>
 {
     extern "rust-call" fn call_once(mut self, args: A) -> R {
         self.call_mut(args)
     }
 }
+
+/// A version of the call operator that takes an immutable receiver.
+#[lang="fn"]
+#[unstable(feature = "core",
+           reason = "uncertain about variadic generics, input versus associated types")]
+#[cfg(not(stage0))]
+pub trait Fn<Args> {
+    type Output;
+
+    /// This is called when the call operator is used.
+    extern "rust-call" fn call(&self, args: Args) -> Self::Output;
+}
+
+/// A version of the call operator that takes a mutable receiver.
+#[lang="fn_mut"]
+#[unstable(feature = "core",
+           reason = "uncertain about variadic generics, input versus associated types")]
+#[cfg(not(stage0))]
+pub trait FnMut<Args> {
+    type Output;
+
+    /// This is called when the call operator is used.
+    extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output;
+}
+
+/// A version of the call operator that takes a by-value receiver.
+#[lang="fn_once"]
+#[unstable(feature = "core",
+           reason = "uncertain about variadic generics, input versus associated types")]
+#[cfg(not(stage0))]
+pub trait FnOnce<Args> {
+    type Output;
+
+    /// This is called when the call operator is used.
+    extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
+}
+
+#[cfg(not(stage0))]
+impl<F: ?Sized, A> FnMut<A> for F
+    where F : Fn<A>
+{
+    type Output = <F as Fn<A>>::Output;
+
+    extern "rust-call" fn call_mut(&mut self, args: A) -> <F as Fn<A>>::Output {
+        self.call(args)
+    }
+}
+
+#[cfg(not(stage0))]
+impl<F,A> FnOnce<A> for F
+    where F : FnMut<A>
+{
+    type Output = <F as FnMut<A>>::Output;
+
+    extern "rust-call" fn call_once(mut self, args: A) -> <F as FnMut<A>>::Output {
+        self.call_mut(args)
+    }
+}

src/libcore/str/mod.rs

@@ -461,13 +461,24 @@ delegate_iter!{exact u8 : Bytes<'a>}
 #[derive(Copy, Clone)]
 struct BytesDeref;
 
+#[cfg(stage0)]
 impl<'a> Fn(&'a u8) -> u8 for BytesDeref {
     #[inline]
     extern "rust-call" fn call(&self, (ptr,): (&'a u8,)) -> u8 {
         *ptr
     }
 }
 
+#[cfg(not(stage0))]
+impl<'a> Fn<(&'a u8,)> for BytesDeref {
+    type Output = u8;
+
+    #[inline]
+    extern "rust-call" fn call(&self, (ptr,): (&'a u8,)) -> u8 {
+        *ptr
+    }
+}
+
 /// An iterator over the substrings of a string, separated by `sep`.
 #[derive(Clone)]
 struct CharSplits<'a, Sep> {