Use match on method args instead of if let

clippy_lints/src/lines_filter_map_ok.rs

@@ -65,7 +65,9 @@ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
             matches!(fm_method_str, "filter_map" | "flat_map" | "flatten") &&
             is_type_diagnostic_item(cx, cx.typeck_results().expr_ty_adjusted(fm_receiver), sym::IoLines)
         {
-            let lint = if let [fm_arg] = fm_args {
+            let lint = match fm_args {
+                [] => fm_method_str == "flatten",
+                [fm_arg] => {
                     match &fm_arg.kind {
                         // Detect `Result::ok`
                         ExprKind::Path(qpath) =>
@@ -84,8 +86,8 @@ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
                             },
                         _ => false,
                     }
-            } else {
-                fm_method_str == "flatten"
+                }
+                _ => false,
             };
 
             if lint {