Some ICE debugging aids

diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index a04b15f8cf13c52385a886956a9d07229c31bd02..eeb2afb0349287f2b9f88e1ca4e0b9427ed79fb1 100644 (file)
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -348,7 +348,7 @@ pub fn fill_single<F>(
         substs.reserve(defs.params.len());
         for param in &defs.params {
             let kind = mk_kind(param, substs);
-            assert_eq!(param.index as usize, substs.len());
+            assert_eq!(param.index as usize, substs.len(), "{substs:#?}, {defs:#?}");
             substs.push(kind);
         }
     }