Normalize before computing ConstArgHasType goal

Author: compiler-errors

compiler/rustc_next_trait_solver/src/solve/mod.rs

@@ -191,6 +191,7 @@ where
         goal: Goal<I, (I::Const, I::Ty)>,
     ) -> QueryResult<I> {
         let (ct, ty) = goal.predicate;
+        let ct = self.structurally_normalize_const(goal.param_env, ct)?;
 
         let ct_ty = match ct.kind() {
             ty::ConstKind::Infer(_) => {

tests/crashes/139905.rs

@@ -0,0 +1,17 @@
+trait A<const B: bool> {}
+impl A<{}> for () {}
+//     ^^ Let's call this "UNEVALUATED".
+
+// During overlap check, we end up trying to prove `(): A<?0c>`. Inference guides
+// `?0c = UNEVALUATED` (which is the `{}` const in the erroneous impl). We then
+// fail to prove `ConstArgHasType<UNEVALUATED, u8>` since `UNEVALUATED` has the
+// type `bool` from the type_of query. We then deeply normalize the predicate for
+// error reporting, which ends up normalizing `UNEVALUATED` to a ConstKind::Error.
+// This ended up ICEing when trying to report an error for the `ConstArgHasType`
+// predicate, since we don't expect `ConstArgHasType(ERROR, Ty)` to ever fail.
+
+trait C<const D: u8> {}
+impl<const D: u8> C<D> for () where (): A<D> {}
+impl<const D: u8> C<D> for () {}
+
+fn main() {}