Remove impl_trait_in_trait_parent

Author: spastorino

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1589,7 +1589,8 @@ fn check_return_position_impl_trait_in_trait_bounds<'tcx>(
             if let ty::GenericArgKind::Type(ty) = arg.unpack()
                 && let ty::Projection(proj) = ty.kind()
                 && tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
-                && tcx.impl_trait_in_trait_parent(proj.item_def_id) == fn_def_id.to_def_id()
+                && let (trait_fn_def_id, _) = tcx.def_path(proj.item_def_id).get_impl_trait_in_trait_data().unwrap()
+                && trait_fn_def_id == fn_def_id.to_def_id()
             {
                 let bounds = wfcx.tcx().explicit_item_bounds(proj.item_def_id);
                 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {

compiler/rustc_middle/src/ty/mod.rs

@@ -2628,14 +2628,6 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn is_const_default_method(self, def_id: DefId) -> bool {
         matches!(self.trait_of_item(def_id), Some(trait_id) if self.has_attr(trait_id, sym::const_trait))
     }
-
-    pub fn impl_trait_in_trait_parent(self, mut def_id: DefId) -> DefId {
-        while let def_kind = self.def_kind(def_id) && def_kind != DefKind::AssocFn {
-            debug_assert_eq!(def_kind, DefKind::ImplTraitPlaceholder);
-            def_id = self.parent(def_id);
-        }
-        def_id
-    }
 }
 
 /// Yields the parent function's `LocalDefId` if `def_id` is an `impl Trait` definition.

compiler/rustc_middle/src/ty/sty.rs

@@ -1148,7 +1148,10 @@ impl<'tcx> ProjectionTy<'tcx> {
         match tcx.def_kind(self.item_def_id) {
             DefKind::AssocTy | DefKind::AssocConst => tcx.parent(self.item_def_id),
             DefKind::ImplTraitPlaceholder => {
-                tcx.parent(tcx.impl_trait_in_trait_parent(self.item_def_id))
+                let (fn_def_id, _) =
+                    tcx.def_path(self.item_def_id).get_impl_trait_in_trait_data().unwrap();
+
+                tcx.parent(fn_def_id)
             }
             kind => bug!("unexpected DefKind in ProjectionTy: {kind:?}"),
         }

compiler/rustc_privacy/src/lib.rs

@@ -129,7 +129,8 @@ where
             projection.trait_ref_and_own_substs(tcx)
         } else {
             // HACK(RPITIT): Remove this when RPITITs are lowered to regular assoc tys
-            let def_id = tcx.impl_trait_in_trait_parent(projection.item_def_id);
+            let (def_id, _) =
+                tcx.def_path(projection.item_def_id).get_impl_trait_in_trait_data().unwrap();
             let trait_generics = tcx.generics_of(def_id);
             (
                 ty::TraitRef { def_id, substs: projection.substs.truncate_to(tcx, trait_generics) },

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1324,13 +1324,8 @@ fn assemble_candidate_for_impl_trait_in_trait<'cx, 'tcx>(
 ) {
     let tcx = selcx.tcx();
     if tcx.def_kind(obligation.predicate.item_def_id) == DefKind::ImplTraitPlaceholder {
-        let trait_fn_def_id = if let Some((fn_def_id, _)) =
-            tcx.def_path(obligation.predicate.item_def_id).get_impl_trait_in_trait_data()
-        {
-            fn_def_id
-        } else {
-            tcx.impl_trait_in_trait_parent(obligation.predicate.item_def_id)
-        };
+        let (trait_fn_def_id, _) =
+            tcx.def_path(obligation.predicate.item_def_id).get_impl_trait_in_trait_data().unwrap();
         // If we are trying to project an RPITIT with trait's default `Self` parameter,
         // then we must be within a default trait body.
         if obligation.predicate.self_ty()
@@ -2238,7 +2233,8 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
     let tcx = selcx.tcx();
     let mut obligations = data.nested;
 
-    let trait_fn_def_id = tcx.impl_trait_in_trait_parent(obligation.predicate.item_def_id);
+    let (trait_fn_def_id, _) =
+        tcx.def_path(obligation.predicate.item_def_id).get_impl_trait_in_trait_data().unwrap();
     let Ok(leaf_def) = assoc_def(selcx, data.impl_def_id, trait_fn_def_id) else {
         return Progress { term: tcx.ty_error().into(), obligations };
     };