1 files changed, 36 insertions, 0 deletions
diff --git a/third_party/rust/futures-0.1.29/src/future/map_err.rs b/third_party/rust/futures-0.1.29/src/future/map_err.rs
new file mode 100644
index 0000000000..4ea12f4586
--- /dev/null
+++ b/third_party/rust/futures-0.1.29/src/future/map_err.rs
@@ -0,0 +1,36 @@
+use {Future, Poll, Async};
+
+/// Future for the `map_err` combinator, changing the error type of a future.
+///
+/// This is created by the `Future::map_err` method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless polled"]
+pub struct MapErr<A, F> where A: Future {
+    future: A,
+    f: Option<F>,
+}
+
+pub fn new<A, F>(future: A, f: F) -> MapErr<A, F>
+    where A: Future
+{
+    MapErr {
+        future: future,
+        f: Some(f),
+    }
+}
+
+impl<U, A, F> Future for MapErr<A, F>
+    where A: Future,
+          F: FnOnce(A::Error) -> U,
+{
+    type Item = A::Item;
+    type Error = U;
+
+    fn poll(&mut self) -> Poll<A::Item, U> {
+        let e = match self.future.poll() {
+            Ok(Async::NotReady) => return Ok(Async::NotReady),
+            other => other,
+        };
+        e.map_err(self.f.take().expect("cannot poll MapErr twice"))
+    }
+}