Rollup merge of rust-lang#113553 - spastorino:smir-types-2, r=oli-obk

Make Placeholder, GeneratorWitness*, Infer and Error unreachable on SMIR rustc_ty_to_ty

Let's remove these todos to not confuse ``@ericmarkmartin`` if they pick some conversion up.

r? ``@oli-obk``

Author: matthiaskrgr

compiler/rustc_smir/src/rustc_smir/mod.rs

@@ -103,21 +103,23 @@ impl<'tcx> Tables<'tcx> {
             ty::Ref(_, _, _) => todo!(),
             ty::FnDef(_, _) => todo!(),
             ty::FnPtr(_) => todo!(),
-            ty::Placeholder(..) => todo!(),
             ty::Dynamic(_, _, _) => todo!(),
             ty::Closure(_, _) => todo!(),
             ty::Generator(_, _, _) => todo!(),
-            ty::GeneratorWitness(_) => todo!(),
-            ty::GeneratorWitnessMIR(_, _) => todo!(),
             ty::Never => todo!(),
             ty::Tuple(fields) => TyKind::RigidTy(RigidTy::Tuple(
                 fields.iter().map(|ty| self.intern_ty(ty)).collect(),
             )),
             ty::Alias(_, _) => todo!(),
             ty::Param(_) => todo!(),
             ty::Bound(_, _) => todo!(),
-            ty::Infer(_) => todo!(),
-            ty::Error(_) => todo!(),
+            ty::Placeholder(..)
+            | ty::GeneratorWitness(_)
+            | ty::GeneratorWitnessMIR(_, _)
+            | ty::Infer(_)
+            | ty::Error(_) => {
+                unreachable!();
+            }
         }
     }