Adding extra check to ignore generic args.

clippy_lints/src/arc_with_non_send_sync.rs

@@ -6,6 +6,7 @@ use if_chain::if_chain;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::LateContext;
 use rustc_lint::LateLintPass;
+use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::sym;
 
@@ -46,6 +47,10 @@ impl LateLintPass<'_> for ArcWithNonSendSync {
             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 match arg_ty.kind() {
+                ty::Param(_) => false,
+                _ => true,
+            };
             if !cx.tcx
                 .lang_items()
                 .sync_trait()

tests/ui/arc_with_non_send_sync.rs

@@ -3,6 +3,11 @@
 use std::cell::RefCell;
 use std::sync::{Arc, Mutex};
 
+fn foo<T>(x: T) {
+    // Should not lint - purposefully ignoring generic args.
+    let a = Arc::new(x);
+}
+
 fn main() {
     // This is safe, as `i32` implements `Send` and `Sync`.
     let a = Arc::new(42);

tests/ui/arc_with_non_send_sync.stderr

@@ -1,10 +1,10 @@
 error: usage of `Arc<T>` where `T` is not `Send` or `Sync`
-  --> $DIR/arc_with_non_send_sync.rs:11:13
+  --> $DIR/arc_with_non_send_sync.rs:16:13
    |
 LL |     let b = Arc::new(RefCell::new(42));
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: consider using `Rc<T>` instead or wrapping `T` in a std::sync type like Mutex<T>
+   = help: consider using `Rc<T>` instead or wrapping `T` in a std::sync type like `Mutex<T>`
    = note: `-D clippy::arc-with-non-send-sync` implied by `-D warnings`
 
 error: aborting due to previous error