use derive(Debug) for TypeTrace

Author: nikomatsakis

src/librustc/infer/mod.rs

@@ -246,7 +246,7 @@ pub enum ValuePairs<'tcx> {
 /// encounter an error or subtyping constraint.
 ///
 /// See the `error_reporting` module for more details.
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct TypeTrace<'tcx> {
     cause: ObligationCause<'tcx>,
     values: ValuePairs<'tcx>,
@@ -1647,12 +1647,6 @@ impl<'tcx> TypeTrace<'tcx> {
     }
 }
 
-impl<'tcx> fmt::Debug for TypeTrace<'tcx> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "TypeTrace({:?})", self.cause)
-    }
-}
-
 impl<'tcx> SubregionOrigin<'tcx> {
     pub fn span(&self) -> Span {
         match *self {