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. It is `Warn` by default.
19 /// **Why is this bad?** This is an unnecessary allocation, and bad for performance. It is only necessary to allocate if you wish to move the box into something.
21 /// **Known problems:** None
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, cx: &LateContext, _: visit::FnKind, decl: &FnDecl, body: &Block, _: Span, id: NodeId) {
47 let param_env = ty::ParameterEnvironment::for_item(cx.tcx, id);
48 let infcx = infer::new_infer_ctxt(cx.tcx, &cx.tcx.tables, Some(param_env), false);
49 let mut v = EscapeDelegate {
54 let mut vis = ExprUseVisitor::new(&mut v, &infcx);
55 vis.walk_fn(decl, body);
60 cx.tcx.map.span(node),
61 "local variable doesn't need to be boxed here");
66 impl<'a, 'tcx: 'a> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
67 fn consume(&mut self, _: NodeId, _: Span, cmt: cmt<'tcx>, mode: ConsumeMode) {
69 if let Categorization::Local(lid) = cmt.cat {
70 if self.set.contains(&lid) {
71 if let Move(DirectRefMove) = mode {
72 // moved out or in. clearly can't be localized
73 self.set.remove(&lid);
78 fn matched_pat(&mut self, _: &Pat, _: cmt<'tcx>, _: MatchMode) {}
79 fn consume_pat(&mut self, consume_pat: &Pat, cmt: cmt<'tcx>, _: ConsumeMode) {
80 if let Categorization::Rvalue(..) = cmt.cat {
81 if let Some(Node::NodeStmt(st)) = self.cx
84 .find(self.cx.tcx.map.get_parent_node(cmt.id)) {
85 if let StmtDecl(ref decl, _) = st.node {
86 if let DeclLocal(ref loc) = decl.node {
87 if let Some(ref ex) = loc.init {
88 if let ExprBox(..) = ex.node {
89 if let ty::TyBox(..) = cmt.ty.sty {
91 self.set.insert(consume_pat.id);
95 // TODO "foo".to_owned() and friends
102 if let Categorization::Local(lid) = cmt.cat {
103 if self.set.contains(&lid) {
104 // let y = x where x is known
105 // remove x, insert y
106 self.set.insert(consume_pat.id);
107 self.set.remove(&lid);
112 fn borrow(&mut self, borrow_id: NodeId, _: Span, cmt: cmt<'tcx>, _: ty::Region, _: ty::BorrowKind,
113 loan_cause: LoanCause) {
115 if let Categorization::Local(lid) = cmt.cat {
116 if self.set.contains(&lid) {
117 if let Some(&AutoAdjustment::AdjustDerefRef(adj)) = self.cx
123 if LoanCause::AutoRef == loan_cause {
125 if adj.autoderefs <= 0 {
126 self.set.remove(&lid); // Used without autodereffing (i.e. x.clone())
129 self.cx.sess().span_bug(cmt.span, "Unknown adjusted AutoRef");
131 } else if LoanCause::AddrOf == loan_cause {
133 if let Some(&AutoAdjustment::AdjustDerefRef(adj)) = self.cx
141 .get_parent_node(borrow_id)) {
142 if adj.autoderefs <= 1 {
143 // foo(&x) where no extra autoreffing is happening
144 self.set.remove(&lid);
148 } else if LoanCause::MatchDiscriminant == loan_cause {
149 self.set.remove(&lid); // `match x` can move
151 // do nothing for matches, etc. These can't escape
155 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
156 fn mutate(&mut self, _: NodeId, _: Span, _: cmt<'tcx>, _: MutateMode) {}