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.
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.
11 //! This file handles the relationships between free regions --
12 //! meaning lifetime parameters. Ordinarily, free regions are
13 //! unrelated to one another, but they can be related via implied or
14 //! explicit bounds. In that case, we track the bounds using the
15 //! `TransitiveRelation` type and use that to decide when one free
16 //! region outlives another and so forth.
18 use hir::def_id::DefId;
19 use middle::region::RegionMaps;
20 use ty::{self, Lift, TyCtxt, Region};
21 use ty::wf::ImpliedBound;
22 use rustc_data_structures::transitive_relation::TransitiveRelation;
24 /// Combines a `RegionMaps` (which governs relationships between
25 /// scopes) and a `FreeRegionMap` (which governs relationships between
26 /// free regions) to yield a complete relation between concrete
29 /// This stuff is a bit convoluted and should be refactored, but as we
30 /// move to NLL it'll all go away anyhow.
31 pub struct RegionRelations<'a, 'gcx: 'tcx, 'tcx: 'a> {
32 pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
34 /// context used to fetch the region maps
37 /// region maps for the given context
38 pub region_maps: &'a RegionMaps<'tcx>,
40 /// free-region relationships
41 pub free_regions: &'a FreeRegionMap<'tcx>,
44 impl<'a, 'gcx, 'tcx> RegionRelations<'a, 'gcx, 'tcx> {
46 tcx: TyCtxt<'a, 'gcx, 'tcx>,
48 region_maps: &'a RegionMaps<'tcx>,
49 free_regions: &'a FreeRegionMap<'tcx>,
59 /// Determines whether one region is a subregion of another. This is intended to run *after
60 /// inference* and sadly the logic is somewhat duplicated with the code in infer.rs.
61 pub fn is_subregion_of(&self,
62 sub_region: ty::Region<'tcx>,
63 super_region: ty::Region<'tcx>)
65 let result = sub_region == super_region || {
66 match (sub_region, super_region) {
71 (&ty::ReScope(sub_scope), &ty::ReScope(super_scope)) =>
72 self.region_maps.is_subscope_of(sub_scope, super_scope),
74 (&ty::ReScope(sub_scope), &ty::ReFree(fr)) => {
75 // 1. It is safe to unwrap `fr.scope` because we
76 // should only ever wind up comparing against
77 // `ReScope` in the context of a method or
78 // body, where `fr.scope` should be `Some`.
79 self.region_maps.is_subscope_of(sub_scope, fr.scope.unwrap() /*1*/) ||
80 self.is_static(super_region)
83 (&ty::ReFree(_), &ty::ReFree(_)) =>
84 self.free_regions.relation.contains(&sub_region, &super_region) ||
85 self.is_static(super_region),
87 (&ty::ReStatic, &ty::ReFree(_)) =>
88 self.is_static(super_region),
94 debug!("is_subregion_of(sub_region={:?}, super_region={:?}) = {:?}",
95 sub_region, super_region, result);
99 /// Determines whether this free-region is required to be 'static
100 fn is_static(&self, super_region: ty::Region<'tcx>) -> bool {
101 debug!("is_static(super_region={:?})", super_region);
102 match *super_region {
103 ty::ReStatic => true,
105 let re_static = self.tcx.mk_region(ty::ReStatic);
106 self.free_regions.relation.contains(&re_static, &super_region)
108 _ => bug!("only free regions should be given to `is_static`")
112 pub fn lub_free_regions(&self,
116 self.free_regions.lub_free_regions(self.tcx, r_a, r_b)
120 #[derive(Clone, RustcEncodable, RustcDecodable)]
121 pub struct FreeRegionMap<'tcx> {
122 // Stores the relation `a < b`, where `a` and `b` are regions.
124 // Invariant: only free regions like `'x` or `'static` are stored
125 // in this relation, not scopes.
126 relation: TransitiveRelation<Region<'tcx>>
129 impl<'tcx> FreeRegionMap<'tcx> {
130 pub fn new() -> Self {
131 FreeRegionMap { relation: TransitiveRelation::new() }
134 pub fn is_empty(&self) -> bool {
135 self.relation.is_empty()
138 pub fn relate_free_regions_from_implied_bounds(&mut self,
139 implied_bounds: &[ImpliedBound<'tcx>])
141 debug!("relate_free_regions_from_implied_bounds()");
142 for implied_bound in implied_bounds {
143 debug!("implied bound: {:?}", implied_bound);
144 match *implied_bound {
145 ImpliedBound::RegionSubRegion(a @ &ty::ReFree(_), b @ &ty::ReFree(_)) |
146 ImpliedBound::RegionSubRegion(a @ &ty::ReStatic, b @ &ty::ReFree(_)) => {
147 self.relate_regions(a, b);
149 ImpliedBound::RegionSubRegion(..) |
150 ImpliedBound::RegionSubParam(..) |
151 ImpliedBound::RegionSubProjection(..) => {
157 pub fn relate_free_regions_from_predicates(&mut self,
158 predicates: &[ty::Predicate<'tcx>]) {
159 debug!("relate_free_regions_from_predicates(predicates={:?})", predicates);
160 for predicate in predicates {
162 ty::Predicate::Projection(..) |
163 ty::Predicate::Trait(..) |
164 ty::Predicate::Equate(..) |
165 ty::Predicate::Subtype(..) |
166 ty::Predicate::WellFormed(..) |
167 ty::Predicate::ObjectSafe(..) |
168 ty::Predicate::ClosureKind(..) |
169 ty::Predicate::TypeOutlives(..) => {
170 // No region bounds here
172 ty::Predicate::RegionOutlives(ty::Binder(ty::OutlivesPredicate(r_a, r_b))) => {
174 // `'static: 'x` is not notable
175 (&ty::ReStatic, &ty::ReFree(_)) => {},
177 (&ty::ReFree(_), &ty::ReStatic) |
178 (&ty::ReFree(_), &ty::ReFree(_)) => {
179 // Record that `'a:'b`. Or, put another way, `'b <= 'a`.
180 self.relate_regions(r_b, r_a);
184 // All named regions are instantiated with free regions.
185 bug!("record_region_bounds: non free region: {:?} / {:?}",
195 fn relate_regions(&mut self, sub: Region<'tcx>, sup: Region<'tcx>) {
196 assert!(match *sub { ty::ReFree(_) | ty::ReStatic => true, _ => false });
197 assert!(match *sup { ty::ReFree(_) | ty::ReStatic => true, _ => false });
198 self.relation.add(sub, sup)
201 pub fn lub_free_regions<'a, 'gcx>(&self,
202 tcx: TyCtxt<'a, 'gcx, 'tcx>,
206 assert!(match *r_a { ty::ReFree(_) => true, _ => false });
207 assert!(match *r_b { ty::ReFree(_) => true, _ => false });
208 let result = if r_a == r_b { r_a } else {
209 match self.relation.postdom_upper_bound(&r_a, &r_b) {
210 None => tcx.mk_region(ty::ReStatic),
214 debug!("lub_free_regions(r_a={:?}, r_b={:?}) = {:?}", r_a, r_b, result);
219 impl_stable_hash_for!(struct FreeRegionMap<'tcx> {
223 impl<'a, 'tcx> Lift<'tcx> for FreeRegionMap<'a> {
224 type Lifted = FreeRegionMap<'tcx>;
225 fn lift_to_tcx<'b, 'gcx>(&self, tcx: TyCtxt<'b, 'gcx, 'tcx>) -> Option<FreeRegionMap<'tcx>> {
226 self.relation.maybe_map(|&fr| fr.lift_to_tcx(tcx))
227 .map(|relation| FreeRegionMap { relation })