Add pretty printer output for `default`

src/librustc_front/print/pprust.rs

@@ -1014,6 +1014,11 @@ pub fn print_impl_item(&mut self, ii: &hir::ImplItem) -> io::Result<()> {
         try!(self.hardbreak_if_not_bol());
         try!(self.maybe_print_comment(ii.span.lo));
         try!(self.print_outer_attributes(&ii.attrs));
+
+        if let hir::Defaultness::Default = ii.defaultness {
+            try!(self.word_nbsp("default"));
+        }
+
         match ii.node {
             hir::ImplItemKind::Const(ref ty, ref expr) => {
                 try!(self.print_associated_const(ii.name, &ty, Some(&expr), ii.vis));

src/libsyntax/print/pprust.rs

@@ -1582,6 +1582,9 @@ pub fn print_impl_item(&mut self, ii: &ast::ImplItem) -> io::Result<()> {
         try!(self.hardbreak_if_not_bol());
         try!(self.maybe_print_comment(ii.span.lo));
         try!(self.print_outer_attributes(&ii.attrs));
+        if let ast::Defaultness::Default = ii.defaultness {
+            try!(self.word_nbsp("default"));
+        }
         match ii.node {
             ast::ImplItemKind::Const(ref ty, ref expr) => {
                 try!(self.print_associated_const(ii.ident, &ty, Some(&expr), ii.vis));

src/test/run-pass/specialization/specialization-default-methods.rs

@@ -63,7 +63,8 @@ fn bar(&self) -> i32 { 0 }
 //                   /  \
 //            Vec<i32>  $Vec<i64>
 
-impl<T> Bar for T {} // use the provided method
+// use the provided method
+impl<T> Bar for T {}
 
 impl Bar for i32 {
     fn bar(&self) -> i32 { 1 }