Rollup merge of #133218 - compiler-errors:const-opaque, r=fee1-dead

Implement `~const` item bounds in RPIT

an RPIT in a `const fn` is allowed to be conditionally const itself :)

r? fee1-dead or reroll

compiler/rustc_hir_analysis/src/check/check.rs

@@ -339,6 +339,8 @@ fn check_opaque_meets_bounds<'tcx>(
 
     let misc_cause = ObligationCause::misc(span, def_id);
     // FIXME: We should just register the item bounds here, rather than equating.
+    // FIXME(const_trait_impl): When we do that, please make sure to also register
+    // the `~const` bounds.
     match ocx.eq(&misc_cause, param_env, opaque_ty, hidden_ty) {
         Ok(()) => {}
         Err(ty_err) => {

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -2083,7 +2083,7 @@ pub(super) fn check_type_bounds<'tcx>(
     // Only in a const implementation do we need to check that the `~const` item bounds hold.
     if tcx.is_conditionally_const(impl_ty_def_id) {
         obligations.extend(
-            tcx.implied_const_bounds(trait_ty.def_id)
+            tcx.explicit_implied_const_bounds(trait_ty.def_id)
                 .iter_instantiated_copied(tcx, rebased_args)
                 .map(|(c, span)| {
                     traits::Obligation::new(