Pass the unadjusted type into the unsize_info function, which seems to be what it expects. Fixes #17322.

src/test/run-pass/issue-17322.rs

@@ -0,0 +1,20 @@
+// 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.
+
+use std::io;
+
+fn f(wr: &mut Writer) {
+    wr.write_str("hello").ok().expect("failed");
+}
+
+fn main() {
+    let mut wr = box io::stdout() as Box<Writer + 'static>;
+    f(&mut wr);
+}