Actually encode default associated types

Fixes #26636

Author: Ariel Ben-Yehuda

src/librustc/metadata/encoder.rs

@@ -1451,6 +1451,10 @@ fn encode_info_for_item(ecx: &EncodeContext,
                     encode_item_sort(rbml_w, 't');
                     encode_family(rbml_w, 'y');
 
+                    if let Some(ty) = associated_type.ty {
+                        encode_type(ecx, rbml_w, ty);
+                    }
+
                     is_nonstatic_method = false;
                 }
             }

src/librustc/middle/traits/project.rs

@@ -904,6 +904,9 @@ fn confirm_impl_candidate<'cx,'tcx>(
                     // ought to be reported by the type checker method
                     // `check_impl_items_against_trait`, so here we
                     // just return TyError.
+                    debug!("confirm_impl_candidate: no associated type {:?} for {:?}",
+                           assoc_ty.name,
+                           trait_ref);
                     return (selcx.tcx().types.err, vec!());
                 }
             }

src/test/auxiliary/xcrate_associated_type_defaults.rs

@@ -0,0 +1,16 @@
+// Copyright 2015 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.
+
+pub trait Foo {
+    type Input = usize;
+    fn bar(&self, _: Self::Input) {}
+}
+
+impl Foo for () {}

src/test/run-pass/xcrate-associated-type-defaults.rs

@@ -0,0 +1,18 @@
+// Copyright 2015 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.
+
+// aux-build:xcrate_associated_type_defaults.rs
+
+extern crate xcrate_associated_type_defaults;
+use xcrate_associated_type_defaults::Foo;
+
+fn main() {
+    ().bar(5);
+}