wip2: remove the error of needing to implement unsizedconstparamty

Author: tiif

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -819,17 +819,9 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &ty::GenericParamDef) -> Result<(), Er
             let span = tcx.def_span(param.def_id);
             let def_id = param.def_id.expect_local();
 
-            if tcx.features().unsized_const_params() {
-                enter_wf_checking_ctxt(tcx, tcx.local_parent(def_id), |wfcx| {
-                    wfcx.register_bound(
-                        ObligationCause::new(span, def_id, ObligationCauseCode::ConstParam(ty)),
-                        wfcx.param_env,
-                        ty,
-                        tcx.require_lang_item(LangItem::UnsizedConstParamTy, span),
-                    );
-                    Ok(())
-                })
-            } else if tcx.features().adt_const_params() {
+            if tcx.features().adt_const_params() || tcx.features().unsized_const_params() {
+                // TODO: should we get rid of the check for LangItem::ConstParamTy? If yes, how should we check
+                // if the trait is implemented.
                 enter_wf_checking_ctxt(tcx, tcx.local_parent(def_id), |wfcx| {
                     wfcx.register_bound(
                         ObligationCause::new(span, def_id, ObligationCauseCode::ConstParam(ty)),

compiler/rustc_trait_selection/src/traits/misc.rs

@@ -102,7 +102,7 @@ pub fn type_allowed_to_implement_const_param_ty<'tcx>(
     lang_item: LangItem,
     parent_cause: ObligationCause<'tcx>,
 ) -> Result<(), ConstParamTyImplementationError<'tcx>> {
-    // FIXME: remove the unsizedconstparamty item
+    // FIXME: core panics if remove unsizedconstparamty, figure out why
     assert_matches!(lang_item, LangItem::ConstParamTy | LangItem::UnsizedConstParamTy);
     let mut need_unstable_feature_bound = false;
 
@@ -123,7 +123,6 @@ pub fn type_allowed_to_implement_const_param_ty<'tcx>(
             need_unstable_feature_bound = true;
             vec![Ty::new_slice(tcx, tcx.types.u8)]
         }
-
         ty::Array(inner_ty, _) => vec![inner_ty],
 
         // `str` morally acts like a newtype around `[u8]`