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.

1 files changed, 8 insertions, 2 deletions

diff --git a/src/libcollectionstest/btree/set.rs b/src/libcollectionstest/btree/set.rs
index 488f0d756d3..234cd6e0fd2 100644
--- a/src/libcollectionstest/btree/set.rs
+++ b/src/libcollectionstest/btree/set.rs
@@ -43,8 +43,6 @@ 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;
@@ -52,6 +50,14 @@ impl<'a, 'b, 'c> FnMut<(&'c i32,)> for Counter<'a, 'b> {
     }
 }
 
+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,