Fix extra_unused_type_parameters lint improperly walking OpaqueDef

Author: mkrasnitski

clippy_lints/src/extra_unused_type_parameters.rs

@@ -2,7 +2,7 @@ use clippy_utils::diagnostics::span_lint;
 use clippy_utils::trait_ref_of_method;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::intravisit::{walk_impl_item, walk_item, walk_param_bound, walk_ty, Visitor};
-use rustc_hir::{GenericParamKind, Generics, ImplItem, ImplItemKind, Item, ItemKind, Ty, WherePredicate};
+use rustc_hir::{GenericParamKind, Generics, ImplItem, ImplItemKind, Item, ItemKind, Ty, TyKind, WherePredicate};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::nested_filter;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -74,6 +74,12 @@ impl<'cx, 'tcx> Visitor<'tcx> for TypeWalker<'cx, 'tcx> {
     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
         if let Some((def_id, _)) = t.peel_refs().as_generic_param() {
             self.map.remove(&def_id);
+        } else if let TyKind::OpaqueDef(id, _, _) = t.kind {
+            // Explicitly walk OpaqueDef. Normally `walk_ty` would do the job, but it calls
+            // `visit_nested_item`, which checks that `Self::NestedFilter::INTER` is set. We're
+            // using `OnlyBodies`, so the check ends up failing and the type isn't fully walked.
+            let item = self.nested_visit_map().item(id);
+            walk_item(self, item);
         } else {
             walk_ty(self, t);
         }