nits

compiler/rustc_middle/src/mir/mod.rs

@@ -2643,6 +2643,7 @@ impl<'tcx> Display for ConstantKind<'tcx> {
         match *self {
             ConstantKind::Ty(c) => pretty_print_const(c, fmt, true),
             ConstantKind::Val(val, ty) => pretty_print_const_value(val, ty, fmt, true),
+            // FIXME(valtrees): Correctly print mir constants.
             ConstantKind::Unevaluated(..) => {
                 fmt.write_str("_")?;
                 Ok(())