Make unreachable path trigger ICE with span

Author: ivarflakstad

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -23,7 +23,7 @@ use super::util::ensure_monomorphic_enough;
 use super::{
     Allocation, AllocId, CheckInAllocMsg, ConstAllocation, ImmTy, InterpCx, InterpResult, Machine, OpTy,
     PlaceTy, Pointer, PointerArithmetic, Provenance, Scalar, err_ub_custom, err_unsup_format,
-    interp_ok, throw_inval, throw_ub_custom, throw_ub_format, throw_unsup_format,
+    interp_ok, throw_inval, throw_ub_custom, throw_ub_format,
 };
 use crate::fluent_generated as fluent;
 
@@ -227,17 +227,15 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
                 ensure_monomorphic_enough(tcx, tp_ty)?;
                 ensure_monomorphic_enough(tcx, result_ty)?;
-
                 let ty::Dynamic(preds, _, ty::Dyn) = result_ty.kind() else {
-                    throw_unsup_format!(
+                    span_bug!(
+                        self.find_closest_untracked_caller_location(),
                         "Invalid type provided to vtable_for::<T, U>. U must be dyn Trait, got {result_ty}."
                     );
                 };
 
-                let (infcx, param_env) = self
-                    .tcx
-                    .infer_ctxt()
-                    .build_with_typing_env(self.typing_env);
+                let (infcx, param_env) =
+                    self.tcx.infer_ctxt().build_with_typing_env(self.typing_env);
 
                 let type_impls_trait = preds.iter().all(|pred| {
                     let trait_ref = ty::TraitRef::new(tcx, pred.def_id(), [tp_ty]);