src/librustc/middle/free_region.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! This file defines
  12
  13 use middle::wf::ImpliedBound;
  14 use middle::ty::{self, FreeRegion};
  15 use util::common::can_reach;
  16 use util::nodemap::{FnvHashMap, FnvHashSet};
  17
  18 #[derive(Clone)]
  19 pub struct FreeRegionMap {
  20     /// `map` maps from a free region `a` to a list of
  21     /// free regions `bs` such that `a <= b for all b in bs`
  22     map: FnvHashMap<FreeRegion, Vec<FreeRegion>>,
  23     /// regions that are required to outlive (and therefore be
  24     /// equal to) 'static.
  25     statics: FnvHashSet<FreeRegion>
  26 }
  27
  28 impl FreeRegionMap {
  29     pub fn new() -> FreeRegionMap {
  30         FreeRegionMap { map: FnvHashMap(), statics: FnvHashSet() }
  31     }
  32
  33     pub fn relate_free_regions_from_implied_bounds<'tcx>(&mut self,
  34                                                         implied_bounds: &[ImpliedBound<'tcx>])
  35     {
  36         debug!("relate_free_regions_from_implied_bounds()");
  37         for implied_bound in implied_bounds {
  38             debug!("implied bound: {:?}", implied_bound);
  39             match *implied_bound {
  40                 ImpliedBound::RegionSubRegion(ty::ReFree(free_a), ty::ReFree(free_b)) => {
  41                     self.relate_free_regions(free_a, free_b);
  42                 }
  43                 ImpliedBound::RegionSubRegion(..) |
  44                 ImpliedBound::RegionSubParam(..) |
  45                 ImpliedBound::RegionSubProjection(..) => {
  46                 }
  47             }
  48         }
  49     }
  50
  51     pub fn relate_free_regions_from_predicates<'tcx>(&mut self,
  52                                                      tcx: &ty::ctxt<'tcx>,
  53                                                      predicates: &[ty::Predicate<'tcx>]) {
  54         debug!("relate_free_regions_from_predicates(predicates={:?})", predicates);
  55         for predicate in predicates {
  56             match *predicate {
  57                 ty::Predicate::Projection(..) |
  58                 ty::Predicate::Trait(..) |
  59                 ty::Predicate::Equate(..) |
  60                 ty::Predicate::WellFormed(..) |
  61                 ty::Predicate::ObjectSafe(..) |
  62                 ty::Predicate::TypeOutlives(..) => {
  63                     // No region bounds here
  64                 }
  65                 ty::Predicate::RegionOutlives(ty::Binder(ty::OutlivesPredicate(r_a, r_b))) => {
  66                     match (r_a, r_b) {
  67                         (ty::ReStatic, ty::ReFree(_)) => {},
  68                         (ty::ReFree(fr_a), ty::ReStatic) => self.relate_to_static(fr_a),
  69                         (ty::ReFree(fr_a), ty::ReFree(fr_b)) => {
  70                             // Record that `'a:'b`. Or, put another way, `'b <= 'a`.
  71                             self.relate_free_regions(fr_b, fr_a);
  72                         }
  73                         _ => {
  74                             // All named regions are instantiated with free regions.
  75                             tcx.sess.bug(
  76                                 &format!("record_region_bounds: non free region: {:?} / {:?}",
  77                                          r_a,
  78                                          r_b));
  79                         }
  80                     }
  81                 }
  82             }
  83         }
  84     }
  85
  86     fn relate_to_static(&mut self, sup: FreeRegion) {
  87         self.statics.insert(sup);
  88     }
  89
  90     fn relate_free_regions(&mut self, sub: FreeRegion, sup: FreeRegion) {
  91        let mut sups = self.map.entry(sub).or_insert(Vec::new());
  92         if !sups.contains(&sup) {
  93             sups.push(sup);
  94         }
  95     }
  96
  97     /// Determines whether two free regions have a subregion relationship
  98     /// by walking the graph encoded in `map`.  Note that
  99     /// it is possible that `sub != sup` and `sub <= sup` and `sup <= sub`
 100     /// (that is, the user can give two different names to the same lifetime).
 101     pub fn sub_free_region(&self, sub: FreeRegion, sup: FreeRegion) -> bool {
 102         can_reach(&self.map, sub, sup) || self.is_static(&sup)
 103     }
 104
 105     /// Determines whether one region is a subregion of another.  This is intended to run *after
 106     /// inference* and sadly the logic is somewhat duplicated with the code in infer.rs.
 107     pub fn is_subregion_of(&self,
 108                            tcx: &ty::ctxt,
 109                            sub_region: ty::Region,
 110                            super_region: ty::Region)
 111                            -> bool {
 112         debug!("is_subregion_of(sub_region={:?}, super_region={:?})",
 113                sub_region, super_region);
 114
 115         sub_region == super_region || {
 116             match (sub_region, super_region) {
 117                 (ty::ReEmpty, _) |
 118                 (_, ty::ReStatic) =>
 119                     true,
 120
 121                 (ty::ReScope(sub_scope), ty::ReScope(super_scope)) =>
 122                     tcx.region_maps.is_subscope_of(sub_scope, super_scope),
 123
 124                 (ty::ReScope(sub_scope), ty::ReFree(ref fr)) =>
 125                     tcx.region_maps.is_subscope_of(sub_scope, fr.scope.to_code_extent()),
 126
 127                 (ty::ReFree(sub_fr), ty::ReFree(super_fr)) =>
 128                     self.sub_free_region(sub_fr, super_fr),
 129
 130                 (ty::ReStatic, ty::ReFree(ref sup_fr)) => self.is_static(sup_fr),
 131
 132                 _ =>
 133                     false,
 134             }
 135         }
 136     }
 137
 138     /// Determines whether this free-region is required to be 'static
 139     pub fn is_static(&self, super_region: &ty::FreeRegion) -> bool {
 140         debug!("is_static(super_region={:?})", super_region);
 141         self.statics.iter().any(|s| can_reach(&self.map, *s, *super_region))
 142     }
 143 }