--- /dev/null
+use rustc_errors::Applicability;
+use rustc_hir::{self as hir, def_id::DefId, GenericArg, QPath, TyKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::TypeFoldable;
+use rustc_span::symbol::sym;
+use rustc_target::abi::LayoutOf;
+use rustc_typeck::hir_ty_to_ty;
+
+use if_chain::if_chain;
+
+use crate::utils::{last_path_segment, snippet, span_lint_and_sugg};
+
+use super::VEC_BOX;
+
+pub(super) fn check(
+ cx: &LateContext<'_>,
+ hir_ty: &hir::Ty<'_>,
+ qpath: &QPath<'_>,
+ def_id: DefId,
+ box_size_threshold: u64,
+) -> bool {
+ if cx.tcx.is_diagnostic_item(sym::vec_type, def_id) {
+ if_chain! {
+ // Get the _ part of Vec<_>
+ if let Some(ref last) = last_path_segment(qpath).args;
+ if let Some(ty) = last.args.iter().find_map(|arg| match arg {
+ GenericArg::Type(ty) => Some(ty),
+ _ => None,
+ });
+ // ty is now _ at this point
+ if let TyKind::Path(ref ty_qpath) = ty.kind;
+ let res = cx.qpath_res(ty_qpath, ty.hir_id);
+ if let Some(def_id) = res.opt_def_id();
+ if Some(def_id) == cx.tcx.lang_items().owned_box();
+ // At this point, we know ty is Box<T>, now get T
+ if let Some(ref last) = last_path_segment(ty_qpath).args;
+ if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
+ GenericArg::Type(ty) => Some(ty),
+ _ => None,
+ });
+ let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
+ if !ty_ty.has_escaping_bound_vars();
+ if ty_ty.is_sized(cx.tcx.at(ty.span), cx.param_env);
+ if let Ok(ty_ty_size) = cx.layout_of(ty_ty).map(|l| l.size.bytes());
+ if ty_ty_size <= box_size_threshold;
+ then {
+ span_lint_and_sugg(
+ cx,
+ VEC_BOX,
+ hir_ty.span,
+ "`Vec<T>` is already on the heap, the boxing is unnecessary",
+ "try",
+ format!("Vec<{}>", snippet(cx, boxed_ty.span, "..")),
+ Applicability::MachineApplicable,
+ );
+ true
+ } else {
+ false
+ }
+ }
+ } else {
+ false
+ }
+}