2 use rustc_front::hir::*;
3 use rustc_front::intravisit as visit;
4 use rustc::front::map::Node;
6 use rustc::middle::ty::adjustment::AutoAdjustment;
7 use rustc::middle::expr_use_visitor::*;
8 use rustc::middle::infer;
9 use rustc::middle::mem_categorization::{cmt, Categorization};
10 use rustc::util::nodemap::NodeSet;
11 use syntax::ast::NodeId;
12 use syntax::codemap::Span;
15 pub struct EscapePass;
17 /// **What it does:** This lint checks for usage of `Box<T>` where an unboxed `T` would work fine
19 /// **Why is this bad?** This is an unnecessary allocation, and bad for performance
21 /// It is only necessary to allocate if you wish to move the box into something.
27 /// let x = Box::new(1);
29 /// println!("{}", *x);
32 declare_lint!(pub BOXED_LOCAL, Warn, "using Box<T> where unnecessary");
34 struct EscapeDelegate<'a, 'tcx: 'a> {
35 cx: &'a LateContext<'a, 'tcx>,
39 impl LintPass for EscapePass {
40 fn get_lints(&self) -> LintArray {
41 lint_array!(BOXED_LOCAL)
45 impl LateLintPass for EscapePass {
46 fn check_fn(&mut self,
53 let param_env = ty::ParameterEnvironment::for_item(cx.tcx, id);
54 let infcx = infer::new_infer_ctxt(cx.tcx, &cx.tcx.tables, Some(param_env), false);
55 let mut v = EscapeDelegate {
60 let mut vis = ExprUseVisitor::new(&mut v, &infcx);
61 vis.walk_fn(decl, body);
66 cx.tcx.map.span(node),
67 "local variable doesn't need to be boxed here");
72 impl<'a, 'tcx: 'a> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
79 if let Categorization::Local(lid) = cmt.cat {
80 if self.set.contains(&lid) {
81 if let Move(DirectRefMove) = mode {
82 // moved out or in. clearly can't be localized
83 self.set.remove(&lid);
88 fn matched_pat(&mut self, _: &Pat, _: cmt<'tcx>, _: MatchMode) {}
89 fn consume_pat(&mut self, consume_pat: &Pat, cmt: cmt<'tcx>, _: ConsumeMode) {
90 if let Categorization::Rvalue(..) = cmt.cat {
91 if let Some(Node::NodeStmt(st)) = self.cx
94 .find(self.cx.tcx.map.get_parent_node(cmt.id)) {
95 if let StmtDecl(ref decl, _) = st.node {
96 if let DeclLocal(ref loc) = decl.node {
97 if let Some(ref ex) = loc.init {
98 if let ExprBox(..) = ex.node {
99 if let ty::TyBox(..) = cmt.ty.sty {
101 self.set.insert(consume_pat.id);
105 // TODO "foo".to_owned() and friends
112 if let Categorization::Local(lid) = cmt.cat {
113 if self.set.contains(&lid) {
114 // let y = x where x is known
115 // remove x, insert y
116 self.set.insert(consume_pat.id);
117 self.set.remove(&lid);
128 loan_cause: LoanCause) {
130 if let Categorization::Local(lid) = cmt.cat {
131 if self.set.contains(&lid) {
132 if let Some(&AutoAdjustment::AdjustDerefRef(adj)) = self.cx
138 if LoanCause::AutoRef == loan_cause {
140 if adj.autoderefs <= 0 {
141 self.set.remove(&lid); // Used without autodereffing (i.e. x.clone())
144 self.cx.sess().span_bug(cmt.span, "Unknown adjusted AutoRef");
146 } else if LoanCause::AddrOf == loan_cause {
148 if let Some(&AutoAdjustment::AdjustDerefRef(adj)) =
149 self.cx.tcx.tables.borrow().adjustments
150 .get(&self.cx.tcx.map.get_parent_node(borrow_id)) {
151 if adj.autoderefs <= 1 {
152 // foo(&x) where no extra autoreffing is happening
153 self.set.remove(&lid);
157 } else if LoanCause::MatchDiscriminant == loan_cause {
158 self.set.remove(&lid); // `match x` can move
160 // do nothing for matches, etc. These can't escape
164 fn decl_without_init(&mut self, _: NodeId, _: Span) {}