Add test for #11881

Closes #11881.

This code has been copied from the original issue and updated for
modern Rust APIs.

src/test/run-pass/issue-11881.rs

@@ -0,0 +1,60 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+extern crate ser = "serialize";
+
+use serialize = self::ser;
+ //necessary for deriving(Encodable)
+use ser::{Encodable, Encoder};
+use ser::json;
+use ser::ebml::writer;
+use std::io::MemWriter;
+use std::str::from_utf8_owned;
+
+#[deriving(Encodable)]
+struct Foo {
+    baz: bool,
+}
+
+#[deriving(Encodable)]
+struct Bar {
+    froboz: uint,
+}
+
+enum WireProtocol {
+    JSON,
+    EBML,
+    // ...
+}
+
+fn encode_json<'a,
+               T: Encodable<json::Encoder<'a>,
+                            std::io::IoError>>(val: &T,
+                                               wr: &'a mut MemWriter) {
+    let mut encoder = json::Encoder::new(wr);
+    val.encode(&mut encoder);
+}
+fn encode_ebml<'a,
+               T: Encodable<writer::Encoder<'a, MemWriter>,
+                            std::io::IoError>>(val: &T,
+                                               wr: &'a mut MemWriter) {
+    let mut encoder = writer::Encoder(wr);
+    val.encode(&mut encoder);
+}
+
+pub fn main() {
+    let target = Foo{baz: false,};
+    let mut wr = MemWriter::new();
+    let proto = JSON;
+    match proto {
+        JSON => encode_json(&target, &mut wr),
+        EBML => encode_ebml(&target, &mut wr)
+    }
+}