[arc_with_non_send_sync]: look for nested type parameters

clippy_lints/src/arc_with_non_send_sync.rs

@@ -7,6 +7,7 @@
 use rustc_lint::LateContext;
 use rustc_lint::LateLintPass;
 use rustc_middle::ty;
+use rustc_middle::ty::GenericArgKind;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::sym;
 
@@ -47,7 +48,10 @@ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
             if let ExprKind::Path(func_path) = func.kind;
             if last_path_segment(&func_path).ident.name == sym::new;
             if let arg_ty = cx.typeck_results().expr_ty(arg);
-            if !matches!(arg_ty.kind(), ty::Param(_));
+            // make sure that the type is not and does not contain any type parameters
+            if arg_ty.walk().all(|arg| {
+                !matches!(arg.unpack(), GenericArgKind::Type(ty) if matches!(ty.kind(), ty::Param(_)))
+            });
             if !cx.tcx
                 .lang_items()
                 .sync_trait()

tests/ui/arc_with_non_send_sync.rs

@@ -7,6 +7,9 @@ fn foo<T>(x: T) {
     // Should not lint - purposefully ignoring generic args.
     let a = Arc::new(x);
 }
+fn issue11076<T>() {
+    let a: Arc<Vec<T>> = Arc::new(Vec::new());
+}
 
 fn main() {
     // This is safe, as `i32` implements `Send` and `Sync`.

tests/ui/arc_with_non_send_sync.stderr

@@ -1,5 +1,5 @@
 error: usage of `Arc<T>` where `T` is not `Send` or `Sync`
-  --> $DIR/arc_with_non_send_sync.rs:16:13
+  --> $DIR/arc_with_non_send_sync.rs:19:13
    |
 LL |     let b = Arc::new(RefCell::new(42));
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^