Fallout from changing fn traits to use inheritance rather than bridge

impls. This is a [breaking-change] (for gated code) in that when you
implement `Fn` (`FnMut`) you must also implement `FnOnce`. This commit
demonstrates how to fix it.

Author: nikomatsakis

src/libcollectionstest/btree/set.rs

@@ -43,15 +43,21 @@ struct Counter<'a, 'b> {
 }
 
 impl<'a, 'b, 'c> FnMut<(&'c i32,)> for Counter<'a, 'b> {
-    type Output = bool;
-
     extern "rust-call" fn call_mut(&mut self, (&x,): (&'c i32,)) -> bool {
         assert_eq!(x, self.expected[*self.i]);
         *self.i += 1;
         true
     }
 }
 
+impl<'a, 'b, 'c> FnOnce<(&'c i32,)> for Counter<'a, 'b> {
+    type Output = bool;
+
+    extern "rust-call" fn call_once(mut self, args: (&'c i32,)) -> bool {
+        self.call_mut(args)
+    }
+}
+
 fn check<F>(a: &[i32], b: &[i32], expected: &[i32], f: F) where
     // FIXME Replace Counter with `Box<FnMut(_) -> _>`
     F: FnOnce(&BTreeSet<i32>, &BTreeSet<i32>, Counter) -> bool,

src/test/compile-fail/borrowck-overloaded-call.rs

@@ -18,26 +18,36 @@ struct SFn {
 }
 
 impl Fn<(isize,)> for SFn {
-    type Output = isize;
-
     extern "rust-call" fn call(&self, (z,): (isize,)) -> isize {
         self.x * self.y * z
     }
 }
 
+impl FnMut<(isize,)> for SFn {
+    extern "rust-call" fn call_mut(&mut self, args: (isize,)) -> isize { self.call(args) }
+}
+
+impl FnOnce<(isize,)> for SFn {
+    type Output = isize;
+    extern "rust-call" fn call_once(self, args: (isize,)) -> isize { self.call(args) }
+}
+
 struct SFnMut {
     x: isize,
     y: isize,
 }
 
 impl FnMut<(isize,)> for SFnMut {
-    type Output = isize;
-
     extern "rust-call" fn call_mut(&mut self, (z,): (isize,)) -> isize {
         self.x * self.y * z
     }
 }
 
+impl FnOnce<(isize,)> for SFnMut {
+    type Output = isize;
+    extern "rust-call" fn call_once(mut self, args: (isize,)) -> isize { self.call_mut(args) }
+}
+
 struct SFnOnce {
     x: String,
 }

src/test/compile-fail/coerce-unsafe-to-closure.rs

@@ -10,5 +10,6 @@
 
 fn main() {
     let x: Option<&[u8]> = Some("foo").map(std::mem::transmute);
-    //~^ ERROR: is not implemented for the type
+    //~^ ERROR E0277
+    //~| ERROR E0277
 }

src/test/compile-fail/extern-wrong-value-type.rs

@@ -18,5 +18,5 @@ fn main() {
     let _x: extern "C" fn() = f; // OK
     is_fn(f);
     //~^ ERROR the trait `core::ops::Fn<()>` is not implemented for the type `extern "C" fn()
-    //~| ERROR the trait `core::ops::Fn<()>` is not implemented for the type `extern "C" fn()
+    //~| ERROR the trait `core::ops::FnOnce<()>` is not implemented for the type `extern "C" fn()
 }

src/test/compile-fail/feature-gate-unboxed-closures-manual-impls.rs

@@ -18,28 +18,21 @@
 struct Foo;
 impl Fn<()> for Foo {
     //~^ ERROR angle-bracket notation is not stable when used with the `Fn` family of traits
-    type Output = ();
-
-    extern "rust-call" fn call(&self, args: ()) -> () {}
+    extern "rust-call" fn call(self, args: ()) -> () {}
 }
 struct Foo1;
-impl Fn() for Foo1 {
+impl FnOnce() for Foo1 {
     //~^ ERROR associated type bindings are not allowed here
-
-    extern "rust-call" fn call(&self, args: ()) -> () {}
+    extern "rust-call" fn call_once(self, args: ()) -> () {}
 }
 struct Bar;
 impl FnMut<()> for Bar {
     //~^ ERROR angle-bracket notation is not stable when used with the `Fn` family of traits
-    type Output = ();
-
     extern "rust-call" fn call_mut(&self, args: ()) -> () {}
 }
 struct Baz;
 impl FnOnce<()> for Baz {
     //~^ ERROR angle-bracket notation is not stable when used with the `Fn` family of traits
-    type Output = ();
-
     extern "rust-call" fn call_once(&self, args: ()) -> () {}
 }
 

src/test/compile-fail/fn-trait-formatting.rs

@@ -35,5 +35,5 @@ fn main() {
 
     needs_fn(1);
     //~^ ERROR `core::ops::Fn<(isize,)>`
-    //~| ERROR `core::ops::Fn<(isize,)>`
+    //~| ERROR `core::ops::FnOnce<(isize,)>`
 }

src/test/compile-fail/fn-variance-1.rs

@@ -17,9 +17,13 @@ fn apply<T, F>(t: T, f: F) where F: FnOnce(T) {
 }
 
 fn main() {
-    apply(&3, takes_mut); //~ ERROR (values differ in mutability)
     apply(&3, takes_imm);
+    apply(&3, takes_mut);
+    //~^ ERROR (values differ in mutability)
+    //~| ERROR (values differ in mutability)
 
     apply(&mut 3, takes_mut);
-    apply(&mut 3, takes_imm); //~ ERROR (values differ in mutability)
+    apply(&mut 3, takes_imm);
+    //~^ ERROR (values differ in mutability)
+    //~| ERROR (values differ in mutability)
 }

src/test/compile-fail/issue-15094.rs

@@ -16,11 +16,10 @@ struct Debuger<T> {
     x: T
 }
 
-impl<T: fmt::Debug> ops::Fn<(),> for Debuger<T> {
+impl<T: fmt::Debug> ops::FnOnce<(),> for Debuger<T> {
     type Output = ();
-
-    fn call(&self, _args: ()) {
-//~^ ERROR `call` has an incompatible type for trait: expected "rust-call" fn, found "Rust" fn
+    fn call_once(self, _args: ()) {
+//~^ ERROR `call_once` has an incompatible type for trait: expected "rust-call" fn, found "Rust" fn
         println!("{:?}", self.x);
     }
 }

src/test/compile-fail/issue-20225.rs

@@ -13,9 +13,19 @@
 struct Foo;
 
 impl<'a, T> Fn<(&'a T,)> for Foo {
+  extern "rust-call" fn call(&self, (_,): (T,)) {}
+  //~^ ERROR: has an incompatible type for trait: expected &-ptr
+}
+
+impl<'a, T> FnMut<(&'a T,)> for Foo {
+  extern "rust-call" fn call_mut(&mut self, (_,): (T,)) {}
+  //~^ ERROR: has an incompatible type for trait: expected &-ptr
+}
+
+impl<'a, T> FnOnce<(&'a T,)> for Foo {
   type Output = ();
 
-  extern "rust-call" fn call(&self, (_,): (T,)) {}
+  extern "rust-call" fn call_once(self, (_,): (T,)) {}
   //~^ ERROR: has an incompatible type for trait: expected &-ptr
 }
 

src/test/compile-fail/overloaded-calls-bad.rs

@@ -18,13 +18,18 @@ struct S {
 }
 
 impl FnMut<(isize,)> for S {
-    type Output = isize;
-
     extern "rust-call" fn call_mut(&mut self, (z,): (isize,)) -> isize {
         self.x * self.y * z
     }
 }
 
+impl FnOnce<(isize,)> for S {
+    type Output = isize;
+    extern "rust-call" fn call_once(mut self, (z,): (isize,)) -> isize {
+        self.call_mut((z,))
+    }
+}
+
 fn main() {
     let mut s = S {
         x: 3,