GenericParam does not need to be a HIR owner.

compiler/rustc_ast_lowering/src/lib.rs

@@ -520,10 +520,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         }
                         self.visit_fn_ret_ty(&f.decl.output)
                     }
-                    TyKind::ImplTrait(def_node_id, _) => {
-                        self.lctx.allocate_hir_id_counter(def_node_id);
-                        visit::walk_ty(self, t);
-                    }
                     _ => visit::walk_ty(self, t),
                 }
             }
@@ -1431,14 +1427,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         // Add a definition for the in-band `Param`.
                         let def_id = self.resolver.local_def_id(def_node_id);
 
-                        self.allocate_hir_id_counter(def_node_id);
+                        let hir_bounds = self.lower_param_bounds(
-
-                        let hir_bounds = self.with_hir_id_owner(def_node_id, |this| {
-                            this.lower_param_bounds(
                             bounds,
                             ImplTraitContext::Universal(in_band_ty_params, parent_def_id),
-                            )
+                        );
-                        });
                         // Set the name to `impl Bound1 + Bound2`.
                         let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
                         in_band_ty_params.push(hir::GenericParam {

compiler/rustc_middle/src/hir/map/collector.rs

@@ -373,27 +373,9 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
     }
 
     fn visit_generic_param(&mut self, param: &'hir GenericParam<'hir>) {
-        if let hir::GenericParamKind::Type {
-            synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
-            ..
-        } = param.kind
-        {
-            debug_assert_eq!(
-                param.hir_id.owner,
-                self.definitions.opt_hir_id_to_local_def_id(param.hir_id).unwrap()
-            );
-            self.with_dep_node_owner(param.hir_id.owner, param, |this, hash| {
-                this.insert_with_hash(param.span, param.hir_id, Node::GenericParam(param), hash);
-
-                this.with_parent(param.hir_id, |this| {
-                    intravisit::walk_generic_param(this, param);
-                });
-            });
-        } else {
         self.insert(param.span, param.hir_id, Node::GenericParam(param));
         intravisit::walk_generic_param(self, param);
     }
-    }
 
     fn visit_trait_item(&mut self, ti: &'hir TraitItem<'hir>) {
         self.with_dep_node_owner(ti.def_id, ti, |this, hash| {

compiler/rustc_passes/src/hir_id_validator.rs

@@ -172,17 +172,4 @@ impl<'a, 'hir> intravisit::Visitor<'hir> for HirIdValidator<'a, 'hir> {
         // we are currently in. So for those it's correct that they have a
         // different owner.
     }
-
-    fn visit_generic_param(&mut self, param: &'hir hir::GenericParam<'hir>) {
-        if let hir::GenericParamKind::Type {
-            synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
-            ..
-        } = param.kind
-        {
-            // Synthetic impl trait parameters are owned by the node of the desugared type.
-            // This means it is correct for them to have a different owner.
-        } else {
-            intravisit::walk_generic_param(self, param);
-        }
-    }
 }

compiler/rustc_save_analysis/src/dump_visitor.rs

@@ -320,15 +320,6 @@ impl<'tcx> DumpVisitor<'tcx> {
         for param in generics.params {
             match param.kind {
                 hir::GenericParamKind::Lifetime { .. } => {}
-                hir::GenericParamKind::Type {
-                    synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
-                    ..
-                } => {
-                    return self
-                        .nest_typeck_results(self.tcx.hir().local_def_id(param.hir_id), |this| {
-                            this.visit_generics(generics)
-                        });
-                }
                 hir::GenericParamKind::Type { .. } => {
                     let param_ss = param.name.ident().span;
                     let name = escape(self.span.snippet(param_ss));