Collect nested items immediately instead of collecting them into an intermediate Vec first

Author: oli-obk

compiler/rustc_ty_utils/src/opaque_types.rs

@@ -103,31 +103,26 @@ impl<'tcx> OpaqueTypeCollector<'tcx> {
         self.tcx.predicates_of(self.item).instantiate_identity(self.tcx).visit_with(self);
         // An item is allowed to constrain opaques declared within its own body (but not nested within
         // nested functions).
-        for id in self.find_taits_declared_in_body() {
-            self.opaques.extend(self.tcx.opaque_types_defined_by(id))
-        }
+        self.collect_taits_declared_in_body();
     }
 
-    #[instrument(level = "trace", skip(self), ret)]
-    fn find_taits_declared_in_body(&self) -> Vec<LocalDefId> {
+    #[instrument(level = "trace", skip(self))]
+    fn collect_taits_declared_in_body(&mut self) {
         let body = self.tcx.hir().body(self.tcx.hir().body_owned_by(self.item)).value;
-        struct TaitInBodyFinder<'tcx> {
-            /// Ids of type aliases found in the body
-            type_aliases: Vec<LocalDefId>,
-            tcx: TyCtxt<'tcx>,
+        struct TaitInBodyFinder<'a, 'tcx> {
+            collector: &'a mut OpaqueTypeCollector<'tcx>,
         }
-        impl<'v> intravisit::Visitor<'v> for TaitInBodyFinder<'_> {
+        impl<'v> intravisit::Visitor<'v> for TaitInBodyFinder<'_, '_> {
             #[instrument(level = "trace", skip(self))]
             fn visit_nested_item(&mut self, id: rustc_hir::ItemId) {
                 let id = id.owner_id.def_id;
-                if let DefKind::TyAlias = self.tcx.def_kind(id) {
-                    self.type_aliases.push(id);
+                if let DefKind::TyAlias = self.collector.tcx.def_kind(id) {
+                    let items = self.collector.tcx.opaque_types_defined_by(id);
+                    self.collector.opaques.extend(items);
                 }
             }
         }
-        let mut visitor = TaitInBodyFinder { type_aliases: Default::default(), tcx: self.tcx };
-        visitor.visit_expr(body);
-        visitor.type_aliases
+        TaitInBodyFinder { collector: self }.visit_expr(body);
     }
 }