1 use rustc::hir::intravisit as visit;
2 use rustc::hir::{self, *};
3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
4 use rustc::middle::expr_use_visitor::*;
5 use rustc::middle::mem_categorization::{cmt_, Categorization};
6 use rustc::ty::layout::LayoutOf;
7 use rustc::ty::{self, Ty};
8 use rustc::util::nodemap::HirIdSet;
9 use rustc::{declare_tool_lint, impl_lint_pass};
10 use syntax::source_map::Span;
12 use crate::utils::span_lint;
14 #[derive(Copy, Clone)]
15 pub struct BoxedLocal {
16 pub too_large_for_stack: u64,
19 declare_clippy_lint! {
20 /// **What it does:** Checks for usage of `Box<T>` where an unboxed `T` would
23 /// **Why is this bad?** This is an unnecessary allocation, and bad for
24 /// performance. It is only necessary to allocate if you wish to move the box
27 /// **Known problems:** None.
31 /// # fn foo(bar: usize) {}
32 /// let x = Box::new(1);
34 /// println!("{}", *x);
38 "using `Box<T>` where unnecessary"
41 fn is_non_trait_box(ty: Ty<'_>) -> bool {
42 ty.is_box() && !ty.boxed_ty().is_trait()
45 struct EscapeDelegate<'a, 'tcx> {
46 cx: &'a LateContext<'a, 'tcx>,
48 too_large_for_stack: u64,
51 impl_lint_pass!(BoxedLocal => [BOXED_LOCAL]);
53 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoxedLocal {
56 cx: &LateContext<'a, 'tcx>,
57 _: visit::FnKind<'tcx>,
63 // If the method is an impl for a trait, don't warn.
64 let parent_id = cx.tcx.hir().get_parent_item(hir_id);
65 let parent_node = cx.tcx.hir().find(parent_id);
67 if let Some(Node::Item(item)) = parent_node {
68 if let ItemKind::Impl(_, _, _, _, Some(..), _, _) = item.kind {
73 let mut v = EscapeDelegate {
75 set: HirIdSet::default(),
76 too_large_for_stack: self.too_large_for_stack,
79 let fn_def_id = cx.tcx.hir().local_def_id(hir_id);
80 let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id);
96 cx.tcx.hir().span(node),
97 "local variable doesn't need to be boxed here",
103 // TODO: Replace with Map::is_argument(..) when it's fixed
104 fn is_argument(map: &hir::map::Map<'_>, id: HirId) -> bool {
106 Some(Node::Binding(_)) => (),
110 match map.find(map.get_parent_node(id)) {
111 Some(Node::Param(_)) => true,
116 impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
117 fn consume(&mut self, _: HirId, _: Span, cmt: &cmt_<'tcx>, mode: ConsumeMode) {
118 if let Categorization::Local(lid) = cmt.cat {
119 if let Move(DirectRefMove) | Move(CaptureMove) = mode {
120 // moved out or in. clearly can't be localized
121 self.set.remove(&lid);
125 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
126 fn consume_pat(&mut self, consume_pat: &Pat, cmt: &cmt_<'tcx>, _: ConsumeMode) {
127 let map = &self.cx.tcx.hir();
128 if is_argument(map, consume_pat.hir_id) {
129 // Skip closure arguments
130 let parent_id = map.get_parent_node(consume_pat.hir_id);
131 if let Some(Node::Expr(..)) = map.find(map.get_parent_node(parent_id)) {
135 if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
136 self.set.insert(consume_pat.hir_id);
140 if let Categorization::Rvalue(..) = cmt.cat {
141 if let Some(Node::Stmt(st)) = map.find(map.get_parent_node(cmt.hir_id)) {
142 if let StmtKind::Local(ref loc) = st.kind {
143 if let Some(ref ex) = loc.init {
144 if let ExprKind::Box(..) = ex.kind {
145 if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
147 self.set.insert(consume_pat.hir_id);
151 // TODO "foo".to_owned() and friends
157 if let Categorization::Local(lid) = cmt.cat {
158 if self.set.contains(&lid) {
159 // let y = x where x is known
160 // remove x, insert y
161 self.set.insert(consume_pat.hir_id);
162 self.set.remove(&lid);
173 loan_cause: LoanCause,
175 if let Categorization::Local(lid) = cmt.cat {
178 // Used without autoderef-ing (i.e., `x.clone()`).
182 // `foo(&x)` where no extra autoref-ing is happening.
185 // `match x` can move.
186 LoanCause::MatchDiscriminant => {
187 self.set.remove(&lid);
190 // Do nothing for matches, etc. These can't escape.
195 fn decl_without_init(&mut self, _: HirId, _: Span) {}
196 fn mutate(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: MutateMode) {}
199 impl<'a, 'tcx> EscapeDelegate<'a, 'tcx> {
200 fn is_large_box(&self, ty: Ty<'tcx>) -> bool {
201 // Large types need to be boxed to avoid stack overflows.
203 self.cx.layout_of(ty.boxed_ty()).ok().map_or(0, |l| l.size.bytes()) > self.too_large_for_stack