rustc_const_eval: improve error handling

Author: BennoLossin

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -10,7 +10,7 @@ use rustc_middle::mir::interpret::{CTFE_ALLOC_SALT, read_target_uint, write_targ
 use rustc_middle::mir::{self, BinOp, ConstValue, NonDivergingIntrinsic, NullOp};
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{Ty, TyCtxt};
-use rustc_middle::{bug, err_inval, ty};
+use rustc_middle::{bug, err_inval, span_bug, ty};
 use rustc_span::{Symbol, sym};
 use tracing::trace;
 
@@ -663,12 +663,16 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         dest: &PlaceTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx, ()> {
         assert_eq!(instance.args.len(), 1);
-        match instance.args.type_at(0).kind() {
+        let ty = instance.args.type_at(0);
+        match ty.kind() {
             &ty::Field(container, field_path) => {
                 let offset = self.nullary_op(NullOp::OffsetOf(field_path), container)?;
                 self.write_immediate(*offset, dest)
             }
-            _ => Err(err_inval!(TooGeneric)).into(),
+            ty::Alias(..) | ty::Param(..) | ty::Placeholder(..) | ty::Infer(..) => {
+                Err(err_inval!(TooGeneric)).into()
+            }
+            _ => span_bug!(self.cur_span(), "expected field representing type, found {ty}"),
         }
     }