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 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.
  17
  18 use infer::outlives::free_region_map::{FreeRegionMap, FreeRegionRelations};
  19 use hir::def_id::DefId;
  20 use middle::region;
  21 use ty::{self, TyCtxt, Region};
  22
  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
  26 /// regions.
  27 ///
  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>,
  32
  33     /// context used to fetch the region maps
  34     pub context: DefId,
  35
  36     /// region maps for the given context
  37     pub region_scope_tree: &'a region::ScopeTree,
  38
  39     /// free-region relationships
  40     pub free_regions: &'a FreeRegionMap<'tcx>,
  41 }
  42
  43 impl<'a, 'gcx, 'tcx> RegionRelations<'a, 'gcx, 'tcx> {
  44     pub fn new(
  45         tcx: TyCtxt<'a, 'gcx, 'tcx>,
  46         context: DefId,
  47         region_scope_tree: &'a region::ScopeTree,
  48         free_regions: &'a FreeRegionMap<'tcx>,
  49     ) -> Self {
  50         Self {
  51             tcx,
  52             context,
  53             region_scope_tree,
  54             free_regions,
  55         }
  56     }
  57
  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>)
  63                            -> bool {
  64         let result = sub_region == super_region || {
  65             match (sub_region, super_region) {
  66                 (ty::ReEmpty, _) |
  67                 (_, ty::ReStatic) =>
  68                     true,
  69
  70                 (ty::ReScope(sub_scope), ty::ReScope(super_scope)) =>
  71                     self.region_scope_tree.is_subscope_of(*sub_scope, *super_scope),
  72
  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)
  76                 }
  77
  78                 (ty::ReScope(sub_scope), ty::ReFree(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)
  81                 }
  82
  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),
  88
  89                 _ =>
  90                     false,
  91             }
  92         };
  93         let result = result || self.is_static(super_region);
  94         debug!("is_subregion_of(sub_region={:?}, super_region={:?}) = {:?}",
  95                sub_region, super_region, result);
  96         result
  97     }
  98
  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.sub_free_regions(&re_static, &super_region)
 107             }
 108             _ => false
 109         }
 110     }
 111
 112     pub fn lub_free_regions(&self,
 113                             r_a: Region<'tcx>,
 114                             r_b: Region<'tcx>)
 115                             -> Region<'tcx> {
 116         self.free_regions.lub_free_regions(self.tcx, r_a, r_b)
 117     }
 118 }
 119