src/escape.rs

   1 use rustc::lint::*;
   2 use rustc_front::hir::*;
   3 use rustc_front::intravisit as visit;
   4 use rustc::front::map::Node;
   5 use rustc::middle::ty;
   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;
  13 use utils::span_lint;
  14
  15 pub struct EscapePass;
  16
  17 declare_lint!(pub BOXED_LOCAL, Warn, "using Box<T> where unnecessary");
  18
  19 struct EscapeDelegate<'a, 'tcx: 'a> {
  20     cx: &'a LateContext<'a, 'tcx>,
  21     set: NodeSet,
  22 }
  23
  24 impl LintPass for EscapePass {
  25     fn get_lints(&self) -> LintArray {
  26         lint_array!(BOXED_LOCAL)
  27     }
  28 }
  29
  30 impl LateLintPass for EscapePass {
  31     fn check_fn(&mut self,
  32                 cx: &LateContext,
  33                 _: visit::FnKind,
  34                 decl: &FnDecl,
  35                 body: &Block,
  36                 _: Span,
  37                 id: NodeId) {
  38         let param_env = ty::ParameterEnvironment::for_item(cx.tcx, id);
  39         let infcx = infer::new_infer_ctxt(cx.tcx, &cx.tcx.tables, Some(param_env), false);
  40         let mut v = EscapeDelegate {
  41             cx: cx,
  42             set: NodeSet(),
  43         };
  44         {
  45             let mut vis = ExprUseVisitor::new(&mut v, &infcx);
  46             vis.walk_fn(decl, body);
  47         }
  48         for node in v.set {
  49             span_lint(cx,
  50                       BOXED_LOCAL,
  51                       cx.tcx.map.span(node),
  52                       "local variable doesn't need to be boxed here");
  53         }
  54     }
  55 }
  56
  57 impl<'a, 'tcx: 'a> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
  58     fn consume(&mut self,
  59                _: NodeId,
  60                _: Span,
  61                cmt: cmt<'tcx>,
  62                mode: ConsumeMode) {
  63
  64         if let Categorization::Local(lid) = cmt.cat {
  65             if self.set.contains(&lid) {
  66                 if let Move(DirectRefMove) = mode {
  67                     // moved out or in. clearly can't be localized
  68                     self.set.remove(&lid);
  69                 }
  70             }
  71         }
  72     }
  73     fn matched_pat(&mut self, _: &Pat, _: cmt<'tcx>, _: MatchMode) {}
  74     fn consume_pat(&mut self, consume_pat: &Pat, cmt: cmt<'tcx>, _: ConsumeMode) {
  75         if let Categorization::Rvalue(..) = cmt.cat {
  76             if let Some(Node::NodeStmt(st)) = self.cx
  77                                                   .tcx
  78                                                   .map
  79                                                   .find(self.cx.tcx.map.get_parent_node(cmt.id)) {
  80                 if let StmtDecl(ref decl, _) = st.node {
  81                     if let DeclLocal(ref loc) = decl.node {
  82                         if let Some(ref ex) = loc.init {
  83                             if let ExprBox(..) = ex.node {
  84                                 if let ty::TyBox(..) = cmt.ty.sty {
  85                                     // let x = box (...)
  86                                     self.set.insert(consume_pat.id);
  87                                 }
  88                                 // TODO Box::new
  89                                 // TODO vec![]
  90                                 // TODO "foo".to_owned() and friends
  91                             }
  92                         }
  93                     }
  94                 }
  95             }
  96         }
  97         if let Categorization::Local(lid) = cmt.cat {
  98             if self.set.contains(&lid) {
  99                 // let y = x where x is known
 100                 // remove x, insert y
 101                 self.set.insert(consume_pat.id);
 102                 self.set.remove(&lid);
 103             }
 104         }
 105
 106     }
 107     fn borrow(&mut self,
 108               borrow_id: NodeId,
 109               _: Span,
 110               cmt: cmt<'tcx>,
 111               _: ty::Region,
 112               _: ty::BorrowKind,
 113               loan_cause: LoanCause) {
 114
 115         if let Categorization::Local(lid) = cmt.cat {
 116             if self.set.contains(&lid) {
 117                 if let Some(&AutoAdjustment::AdjustDerefRef(adj)) = self.cx
 118                                                                         .tcx
 119                                                                         .tables
 120                                                                         .borrow()
 121                                                                         .adjustments
 122                                                                         .get(&borrow_id) {
 123                     if LoanCause::AutoRef == loan_cause {
 124                         // x.foo()
 125                         if adj.autoderefs <= 0 {
 126                             self.set.remove(&lid); // Used without autodereffing (i.e. x.clone())
 127                         }
 128                     } else {
 129                         self.cx.sess().span_bug(cmt.span, "Unknown adjusted AutoRef");
 130                     }
 131                 } else if LoanCause::AddrOf == loan_cause {
 132                     // &x
 133                     if let Some(&AutoAdjustment::AdjustDerefRef(adj)) =
 134                            self.cx.tcx.tables.borrow().adjustments
 135                                .get(&self.cx.tcx.map.get_parent_node(borrow_id)) {
 136                         if adj.autoderefs <= 1 {
 137                             // foo(&x) where no extra autoreffing is happening
 138                             self.set.remove(&lid);
 139                         }
 140                     }
 141
 142                 } else if LoanCause::MatchDiscriminant == loan_cause {
 143                     self.set.remove(&lid); // `match x` can move
 144                 }
 145                 // do nothing for matches, etc. These can't escape
 146             }
 147         }
 148     }
 149     fn decl_without_init(&mut self, _: NodeId, _: Span) {}
 150     fn mutate(&mut self,
 151               _: NodeId,
 152               _: Span,
 153               _: cmt<'tcx>,
 154               _: MutateMode) {
 155     }
 156 }