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::ty::{self, FreeRegion, Region};
  14 use middle::wf::ImpliedBound;
  15 use rustc_data_structures::transitive_relation::TransitiveRelation;
  16
  17 #[derive(Clone)]
  18 pub struct FreeRegionMap {
  19     // Stores the relation `a < b`, where `a` and `b` are regions.
  20     relation: TransitiveRelation<Region>
  21 }
  22
  23 impl FreeRegionMap {
  24     pub fn new() -> FreeRegionMap {
  25         FreeRegionMap { relation: TransitiveRelation::new() }
  26     }
  27
  28     pub fn relate_free_regions_from_implied_bounds<'tcx>(&mut self,
  29                                                         implied_bounds: &[ImpliedBound<'tcx>])
  30     {
  31         debug!("relate_free_regions_from_implied_bounds()");
  32         for implied_bound in implied_bounds {
  33             debug!("implied bound: {:?}", implied_bound);
  34             match *implied_bound {
  35                 ImpliedBound::RegionSubRegion(ty::ReFree(free_a), ty::ReFree(free_b)) => {
  36                     self.relate_free_regions(free_a, free_b);
  37                 }
  38                 ImpliedBound::RegionSubRegion(..) |
  39                 ImpliedBound::RegionSubParam(..) |
  40                 ImpliedBound::RegionSubProjection(..) => {
  41                 }
  42             }
  43         }
  44     }
  45
  46     pub fn relate_free_regions_from_predicates<'tcx>(&mut self,
  47                                                      tcx: &ty::ctxt<'tcx>,
  48                                                      predicates: &[ty::Predicate<'tcx>]) {
  49         debug!("relate_free_regions_from_predicates(predicates={:?})", predicates);
  50         for predicate in predicates {
  51             match *predicate {
  52                 ty::Predicate::Projection(..) |
  53                 ty::Predicate::Trait(..) |
  54                 ty::Predicate::Equate(..) |
  55                 ty::Predicate::WellFormed(..) |
  56                 ty::Predicate::ObjectSafe(..) |
  57                 ty::Predicate::TypeOutlives(..) => {
  58                     // No region bounds here
  59                 }
  60                 ty::Predicate::RegionOutlives(ty::Binder(ty::OutlivesPredicate(r_a, r_b))) => {
  61                     match (r_a, r_b) {
  62                         (ty::ReStatic, ty::ReFree(_)) => {},
  63                         (ty::ReFree(fr_a), ty::ReStatic) => self.relate_to_static(fr_a),
  64                         (ty::ReFree(fr_a), ty::ReFree(fr_b)) => {
  65                             // Record that `'a:'b`. Or, put another way, `'b <= 'a`.
  66                             self.relate_free_regions(fr_b, fr_a);
  67                         }
  68                         _ => {
  69                             // All named regions are instantiated with free regions.
  70                             tcx.sess.bug(
  71                                 &format!("record_region_bounds: non free region: {:?} / {:?}",
  72                                          r_a,
  73                                          r_b));
  74                         }
  75                     }
  76                 }
  77             }
  78         }
  79     }
  80
  81     fn relate_to_static(&mut self, sup: FreeRegion) {
  82         self.relation.add(ty::ReStatic, ty::ReFree(sup));
  83     }
  84
  85     fn relate_free_regions(&mut self, sub: FreeRegion, sup: FreeRegion) {
  86         self.relation.add(ty::ReFree(sub), ty::ReFree(sup))
  87     }
  88
  89     /// Determines whether two free regions have a subregion relationship
  90     /// by walking the graph encoded in `map`.  Note that
  91     /// it is possible that `sub != sup` and `sub <= sup` and `sup <= sub`
  92     /// (that is, the user can give two different names to the same lifetime).
  93     pub fn sub_free_region(&self, sub: FreeRegion, sup: FreeRegion) -> bool {
  94         let result = sub == sup || {
  95             let sub = ty::ReFree(sub);
  96             let sup = ty::ReFree(sup);
  97             self.relation.contains(&sub, &sup) || self.relation.contains(&ty::ReStatic, &sup)
  98         };
  99         debug!("sub_free_region(sub={:?}, sup={:?}) = {:?}", sub, sup, result);
 100         result
 101     }
 102
 103     pub fn lub_free_regions(&self, fr_a: FreeRegion, fr_b: FreeRegion) -> Region {
 104         let r_a = ty::ReFree(fr_a);
 105         let r_b = ty::ReFree(fr_b);
 106         let result = if fr_a == fr_b { r_a } else {
 107             match self.relation.best_upper_bound(&r_a, &r_b) {
 108                 None => ty::ReStatic,
 109                 Some(r) => *r,
 110             }
 111         };
 112         debug!("lub_free_regions(fr_a={:?}, fr_b={:?}) = {:?}", fr_a, fr_b, result);
 113         result
 114     }
 115
 116     /// Determines whether one region is a subregion of another.  This is intended to run *after
 117     /// inference* and sadly the logic is somewhat duplicated with the code in infer.rs.
 118     pub fn is_subregion_of(&self,
 119                            tcx: &ty::ctxt,
 120                            sub_region: ty::Region,
 121                            super_region: ty::Region)
 122                            -> bool {
 123         let result = sub_region == super_region || {
 124             match (sub_region, super_region) {
 125                 (ty::ReEmpty, _) |
 126                 (_, ty::ReStatic) =>
 127                     true,
 128
 129                 (ty::ReScope(sub_scope), ty::ReScope(super_scope)) =>
 130                     tcx.region_maps.is_subscope_of(sub_scope, super_scope),
 131
 132                 (ty::ReScope(sub_scope), ty::ReFree(fr)) =>
 133                     tcx.region_maps.is_subscope_of(sub_scope, fr.scope.to_code_extent()) ||
 134                     self.is_static(fr),
 135
 136                 (ty::ReFree(sub_fr), ty::ReFree(super_fr)) =>
 137                     self.sub_free_region(sub_fr, super_fr),
 138
 139                 (ty::ReStatic, ty::ReFree(sup_fr)) =>
 140                     self.is_static(sup_fr),
 141
 142                 _ =>
 143                     false,
 144             }
 145         };
 146         debug!("is_subregion_of(sub_region={:?}, super_region={:?}) = {:?}",
 147                sub_region, super_region, result);
 148         result
 149     }
 150
 151     /// Determines whether this free-region is required to be 'static
 152     pub fn is_static(&self, super_region: ty::FreeRegion) -> bool {
 153         debug!("is_static(super_region={:?})", super_region);
 154         self.relation.contains(&ty::ReStatic, &ty::ReFree(super_region))
 155     }
 156 }
 157
 158 #[cfg(test)]
 159 fn free_region(index: u32) -> FreeRegion {
 160     use middle::region::DestructionScopeData;
 161     FreeRegion { scope: DestructionScopeData::new(0),
 162                  bound_region: ty::BoundRegion::BrAnon(index) }
 163 }
 164
 165 #[test]
 166 fn lub() {
 167     // a very VERY basic test, but see the tests in
 168     // TransitiveRelation, which are much more thorough.
 169     let frs: Vec<_> = (0..3).map(|i| free_region(i)).collect();
 170     let mut map = FreeRegionMap::new();
 171     map.relate_free_regions(frs[0], frs[2]);
 172     map.relate_free_regions(frs[1], frs[2]);
 173     assert_eq!(map.lub_free_regions(frs[0], frs[1]), ty::ReFree(frs[2]));
 174 }
 175