1 files changed, 54 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/types/box_collection.rs b/src/tools/clippy/clippy_lints/src/types/box_collection.rs
new file mode 100644
index 000000000..ba51404d2
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/types/box_collection.rs
@@ -0,0 +1,54 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::{path_def_id, qpath_generic_tys};
+use rustc_hir::{self as hir, def_id::DefId, QPath};
+use rustc_lint::LateContext;
+use rustc_span::{sym, Symbol};
+
+use super::BOX_COLLECTION;
+
+pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, qpath: &QPath<'_>, def_id: DefId) -> bool {
+    if_chain! {
+        if Some(def_id) == cx.tcx.lang_items().owned_box();
+        if let Some(item_type) = get_std_collection(cx, qpath);
+        then {
+            let generic = match item_type {
+                sym::String => "",
+                _ => "<..>",
+            };
+
+            let box_content = format!("{outer}{generic}", outer = item_type);
+            span_lint_and_help(
+                cx,
+                BOX_COLLECTION,
+                hir_ty.span,
+                &format!(
+                    "you seem to be trying to use `Box<{box_content}>`. Consider using just `{box_content}`"),
+                None,
+                &format!(
+                    "`{box_content}` is already on the heap, `Box<{box_content}>` makes an extra allocation")
+            );
+            true
+        } else {
+            false
+        }
+    }
+}
+
+fn get_std_collection(cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<Symbol> {
+    let param = qpath_generic_tys(qpath).next()?;
+    let id = path_def_id(cx, param)?;
+    cx.tcx.get_diagnostic_name(id).filter(|&name| {
+        matches!(
+            name,
+            sym::HashMap
+                | sym::String
+                | sym::Vec
+                | sym::HashSet
+                | sym::VecDeque
+                | sym::LinkedList
+                | sym::BTreeMap
+                | sym::BTreeSet
+                | sym::BinaryHeap
+        )
+    })
+}