Make main span in impl-trait ciclic reference point to def_span

src/librustc/ty/maps/plumbing.rs

@@ -81,6 +81,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         // (And cycle errors around impls tend to occur during the
         // collect/coherence phases anyhow.)
         item_path::with_forced_impl_filename_line(|| {
+            let span = self.sess.codemap().def_span(span);
             let mut err =
                 struct_span_err!(self.sess, span, E0391,
                                  "unsupported cyclic reference between types/traits detected");

src/test/ui/impl-trait/auto-trait-leak.stderr

@@ -23,14 +23,8 @@ error[E0277]: the trait bound `std::rc::Rc<std::cell::Cell<i32>>: std::marker::S
 error[E0391]: unsupported cyclic reference between types/traits detected
   --> $DIR/auto-trait-leak.rs:52:1
    |
-52 | / fn cycle1() -> impl Clone {
-53 | |     //~^ ERROR unsupported cyclic reference between types/traits detected
-54 | |     //~| cyclic reference
-55 | |     //~| NOTE the cycle begins when processing `cycle1`...
-...  |
-60 | |     Rc::new(Cell::new(5))
-61 | | }
-   | |_^ cyclic reference
+52 | fn cycle1() -> impl Clone {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^ cyclic reference
    |
 note: the cycle begins when processing `cycle1`...
   --> $DIR/auto-trait-leak.rs:52:1