src/librustc/middle/free_region.rs

   1 //! This module handles the relationships between "free regions", i.e., lifetime parameters.
   2 //! Ordinarily, free regions are unrelated to one another, but they can be related via implied
   3 //! or explicit bounds. In that case, we track the bounds using the `TransitiveRelation` type,
   4 //! and use that to decide when one free region outlives another, and so forth.
   5
   6 use crate::infer::outlives::free_region_map::{FreeRegionMap, FreeRegionRelations};
   7 use crate::hir::def_id::DefId;
   8 use crate::middle::region;
   9 use crate::ty::{self, TyCtxt, Region};
  10
  11 /// Combines a `region::ScopeTree` (which governs relationships between
  12 /// scopes) and a `FreeRegionMap` (which governs relationships between
  13 /// free regions) to yield a complete relation between concrete
  14 /// regions.
  15 ///
  16 /// This stuff is a bit convoluted and should be refactored, but as we
  17 /// transition to NLL, it'll all go away anyhow.
  18 pub struct RegionRelations<'a, 'gcx: 'tcx, 'tcx: 'a> {
  19     pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
  20
  21     /// The context used to fetch the region maps.
  22     pub context: DefId,
  23
  24     /// The region maps for the given context.
  25     pub region_scope_tree: &'a region::ScopeTree,
  26
  27     /// Free-region relationships.
  28     pub free_regions: &'a FreeRegionMap<'tcx>,
  29 }
  30
  31 impl<'a, 'gcx, 'tcx> RegionRelations<'a, 'gcx, 'tcx> {
  32     pub fn new(
  33         tcx: TyCtxt<'a, 'gcx, 'tcx>,
  34         context: DefId,
  35         region_scope_tree: &'a region::ScopeTree,
  36         free_regions: &'a FreeRegionMap<'tcx>,
  37     ) -> Self {
  38         Self {
  39             tcx,
  40             context,
  41             region_scope_tree,
  42             free_regions,
  43         }
  44     }
  45
  46     /// Determines whether one region is a subregion of another. This is intended to run *after
  47     /// inference* and sadly the logic is somewhat duplicated with the code in infer.rs.
  48     pub fn is_subregion_of(&self,
  49                            sub_region: ty::Region<'tcx>,
  50                            super_region: ty::Region<'tcx>)
  51                            -> bool {
  52         let result = sub_region == super_region || {
  53             match (sub_region, super_region) {
  54                 (ty::ReEmpty, _) |
  55                 (_, ty::ReStatic) =>
  56                     true,
  57
  58                 (ty::ReScope(sub_scope), ty::ReScope(super_scope)) =>
  59                     self.region_scope_tree.is_subscope_of(*sub_scope, *super_scope),
  60
  61                 (ty::ReScope(sub_scope), ty::ReEarlyBound(ref br)) => {
  62                     let fr_scope = self.region_scope_tree.early_free_scope(self.tcx, br);
  63                     self.region_scope_tree.is_subscope_of(*sub_scope, fr_scope)
  64                 }
  65
  66                 (ty::ReScope(sub_scope), ty::ReFree(fr)) => {
  67                     let fr_scope = self.region_scope_tree.free_scope(self.tcx, fr);
  68                     self.region_scope_tree.is_subscope_of(*sub_scope, fr_scope)
  69                 }
  70
  71                 (ty::ReEarlyBound(_), ty::ReEarlyBound(_)) |
  72                 (ty::ReFree(_), ty::ReEarlyBound(_)) |
  73                 (ty::ReEarlyBound(_), ty::ReFree(_)) |
  74                 (ty::ReFree(_), ty::ReFree(_)) =>
  75                     self.free_regions.sub_free_regions(sub_region, super_region),
  76
  77                 _ =>
  78                     false,
  79             }
  80         };
  81         let result = result || self.is_static(super_region);
  82         debug!("is_subregion_of(sub_region={:?}, super_region={:?}) = {:?}",
  83                sub_region, super_region, result);
  84         result
  85     }
  86
  87     /// Determines whether this free region is required to be `'static`.
  88     fn is_static(&self, super_region: ty::Region<'tcx>) -> bool {
  89         debug!("is_static(super_region={:?})", super_region);
  90         match *super_region {
  91             ty::ReStatic => true,
  92             ty::ReEarlyBound(_) | ty::ReFree(_) => {
  93                 let re_static = self.tcx.mk_region(ty::ReStatic);
  94                 self.free_regions.sub_free_regions(&re_static, &super_region)
  95             }
  96             _ => false
  97         }
  98     }
  99
 100     pub fn lub_free_regions(&self,
 101                             r_a: Region<'tcx>,
 102                             r_b: Region<'tcx>)
 103                             -> Region<'tcx> {
 104         self.free_regions.lub_free_regions(self.tcx, r_a, r_b)
 105     }
 106 }