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;
20 use ty::{self, Lift, TyCtxt, Region};
21 use rustc_data_structures::transitive_relation::TransitiveRelation;
23 /// Combines a `region::ScopeTree` (which governs relationships between
24 /// scopes) and a `FreeRegionMap` (which governs relationships between
25 /// free regions) to yield a complete relation between concrete
28 /// This stuff is a bit convoluted and should be refactored, but as we
29 /// move to NLL it'll all go away anyhow.
30 pub struct RegionRelations<'a, 'gcx: 'tcx, 'tcx: 'a> {
31 pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
33 /// context used to fetch the region maps
36 /// region maps for the given context
37 pub region_scope_tree: &'a region::ScopeTree,
39 /// free-region relationships
40 pub free_regions: &'a FreeRegionMap<'tcx>,
43 impl<'a, 'gcx, 'tcx> RegionRelations<'a, 'gcx, 'tcx> {
45 tcx: TyCtxt<'a, 'gcx, 'tcx>,
47 region_scope_tree: &'a region::ScopeTree,
48 free_regions: &'a FreeRegionMap<'tcx>,
58 /// Determines whether one region is a subregion of another. This is intended to run *after
59 /// inference* and sadly the logic is somewhat duplicated with the code in infer.rs.
60 pub fn is_subregion_of(&self,
61 sub_region: ty::Region<'tcx>,
62 super_region: ty::Region<'tcx>)
64 let result = sub_region == super_region || {
65 match (sub_region, super_region) {
70 (&ty::ReScope(sub_scope), &ty::ReScope(super_scope)) =>
71 self.region_scope_tree.is_subscope_of(sub_scope, super_scope),
73 (&ty::ReScope(sub_scope), &ty::ReEarlyBound(ref br)) => {
74 let fr_scope = self.region_scope_tree.early_free_scope(self.tcx, br);
75 self.region_scope_tree.is_subscope_of(sub_scope, fr_scope)
78 (&ty::ReScope(sub_scope), &ty::ReFree(ref fr)) => {
79 let fr_scope = self.region_scope_tree.free_scope(self.tcx, fr);
80 self.region_scope_tree.is_subscope_of(sub_scope, fr_scope)
83 (&ty::ReEarlyBound(_), &ty::ReEarlyBound(_)) |
84 (&ty::ReFree(_), &ty::ReEarlyBound(_)) |
85 (&ty::ReEarlyBound(_), &ty::ReFree(_)) |
86 (&ty::ReFree(_), &ty::ReFree(_)) =>
87 self.free_regions.sub_free_regions(&sub_region, &super_region),
93 let result = result || 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,
104 ty::ReEarlyBound(_) | ty::ReFree(_) => {
105 let re_static = self.tcx.mk_region(ty::ReStatic);
106 self.free_regions.relation.contains(&re_static, &super_region)
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, Debug)]
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_predicates(&mut self,
139 predicates: &[ty::Predicate<'tcx>]) {
140 debug!("relate_free_regions_from_predicates(predicates={:?})", predicates);
141 for predicate in predicates {
143 ty::Predicate::Projection(..) |
144 ty::Predicate::Trait(..) |
145 ty::Predicate::Equate(..) |
146 ty::Predicate::Subtype(..) |
147 ty::Predicate::WellFormed(..) |
148 ty::Predicate::ObjectSafe(..) |
149 ty::Predicate::ClosureKind(..) |
150 ty::Predicate::TypeOutlives(..) |
151 ty::Predicate::ConstEvaluatable(..) => {
152 // No region bounds here
154 ty::Predicate::RegionOutlives(ty::Binder(ty::OutlivesPredicate(r_a, r_b))) => {
155 self.relate_regions(r_b, r_a);
161 /// Record that `'sup:'sub`. Or, put another way, `'sub <= 'sup`.
162 /// (with the exception that `'static: 'x` is not notable)
163 pub fn relate_regions(&mut self, sub: Region<'tcx>, sup: Region<'tcx>) {
164 debug!("relate_regions(sub={:?}, sup={:?})", sub, sup);
165 if (is_free(sub) || *sub == ty::ReStatic) && is_free(sup) {
166 self.relation.add(sub, sup)
170 /// True if `r_a <= r_b` is known to hold. Both `r_a` and `r_b`
171 /// must be free regions from the function header.
172 pub fn sub_free_regions<'a, 'gcx>(&self,
176 debug!("sub_free_regions(r_a={:?}, r_b={:?})", r_a, r_b);
177 assert!(is_free(r_a));
178 assert!(is_free(r_b));
179 let result = r_a == r_b || self.relation.contains(&r_a, &r_b);
180 debug!("sub_free_regions: result={}", result);
184 /// Compute the least-upper-bound of two free regions. In some
185 /// cases, this is more conservative than necessary, in order to
186 /// avoid making arbitrary choices. See
187 /// `TransitiveRelation::postdom_upper_bound` for more details.
188 pub fn lub_free_regions<'a, 'gcx>(&self,
189 tcx: TyCtxt<'a, 'gcx, 'tcx>,
193 debug!("lub_free_regions(r_a={:?}, r_b={:?})", r_a, r_b);
194 assert!(is_free(r_a));
195 assert!(is_free(r_b));
196 let result = if r_a == r_b { r_a } else {
197 match self.relation.postdom_upper_bound(&r_a, &r_b) {
198 None => tcx.mk_region(ty::ReStatic),
202 debug!("lub_free_regions(r_a={:?}, r_b={:?}) = {:?}", r_a, r_b, result);
206 /// Returns all regions that are known to outlive `r_a`. For
207 /// example, in a function:
210 /// fn foo<'a, 'b: 'a, 'c: 'b>() { .. }
213 /// if `r_a` represents `'a`, this function would return `{'b, 'c}`.
214 pub fn regions_that_outlive<'a, 'gcx>(&self, r_a: Region<'tcx>) -> Vec<&Region<'tcx>> {
215 assert!(is_free(r_a) || *r_a == ty::ReStatic);
216 self.relation.greater_than(&r_a)
220 fn is_free(r: Region) -> bool {
222 ty::ReEarlyBound(_) | ty::ReFree(_) => true,
227 impl_stable_hash_for!(struct FreeRegionMap<'tcx> {
231 impl<'a, 'tcx> Lift<'tcx> for FreeRegionMap<'a> {
232 type Lifted = FreeRegionMap<'tcx>;
233 fn lift_to_tcx<'b, 'gcx>(&self, tcx: TyCtxt<'b, 'gcx, 'tcx>) -> Option<FreeRegionMap<'tcx>> {
234 self.relation.maybe_map(|&fr| fr.lift_to_tcx(tcx))
235 .map(|relation| FreeRegionMap { relation })