2 files changed, 7 insertions, 2 deletions
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index c43162f6325..2ba365e298f 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -1349,9 +1349,8 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// #![feature(box_syntax)]
     /// fn main() {
-    ///     let a = (box [1, 2, 3]).len();
+    ///     let a = Box::new([1, 2, 3]).len();
     /// }
     /// ```
     ///
@@ -1373,6 +1372,11 @@ impl<'tcx> LateLintPass<'tcx> for UnusedAllocation {
     fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
         match e.kind {
             hir::ExprKind::Box(_) => {}
+            hir::ExprKind::Call(path_expr, [_])
+                if let hir::ExprKind::Path(qpath) = &path_expr.kind
+                && let Some(did) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()
+                && cx.tcx.is_diagnostic_item(sym::box_new, did)
+                => {}
             _ => return,
         }
 
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 4e626fd9f30..bf27bd6c5ad 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -429,6 +429,7 @@ symbols! {
         borrowck_graphviz_format,
         borrowck_graphviz_postflow,
         box_free,
+        box_new,
         box_patterns,
         box_syntax,
         bpf_target_feature,