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::middle::region;
   7 use crate::ty::free_region_map::{FreeRegionMap, FreeRegionRelations};
   8 use crate::ty::{self, Region, TyCtxt};
   9 use rustc_hir::def_id::DefId;
  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, 'tcx> {
  19     pub tcx: TyCtxt<'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, 'tcx> RegionRelations<'a, 'tcx> {
  32     pub fn new(
  33         tcx: TyCtxt<'tcx>,
  34         context: DefId,
  35         region_scope_tree: &'a region::ScopeTree,
  36         free_regions: &'a FreeRegionMap<'tcx>,
  37     ) -> Self {
  38         Self { tcx, context, region_scope_tree, free_regions }
  39     }
  40
  41     /// Determines whether one region is a subregion of another. This is intended to run *after
  42     /// inference* and sadly the logic is somewhat duplicated with the code in infer.rs.
  43     pub fn is_subregion_of(
  44         &self,
  45         sub_region: ty::Region<'tcx>,
  46         super_region: ty::Region<'tcx>,
  47     ) -> bool {
  48         let result = sub_region == super_region || {
  49             match (sub_region, super_region) {
  50                 (ty::ReEmpty, _) | (_, ty::ReStatic) => true,
  51
  52                 (ty::ReScope(sub_scope), ty::ReScope(super_scope)) => {
  53                     self.region_scope_tree.is_subscope_of(*sub_scope, *super_scope)
  54                 }
  55
  56                 (ty::ReScope(sub_scope), ty::ReEarlyBound(ref br)) => {
  57                     let fr_scope = self.region_scope_tree.early_free_scope(self.tcx, br);
  58                     self.region_scope_tree.is_subscope_of(*sub_scope, fr_scope)
  59                 }
  60
  61                 (ty::ReScope(sub_scope), ty::ReFree(fr)) => {
  62                     let fr_scope = self.region_scope_tree.free_scope(self.tcx, fr);
  63                     self.region_scope_tree.is_subscope_of(*sub_scope, fr_scope)
  64                 }
  65
  66                 (ty::ReEarlyBound(_), ty::ReEarlyBound(_))
  67                 | (ty::ReFree(_), ty::ReEarlyBound(_))
  68                 | (ty::ReEarlyBound(_), ty::ReFree(_))
  69                 | (ty::ReFree(_), ty::ReFree(_)) => {
  70                     self.free_regions.sub_free_regions(sub_region, super_region)
  71                 }
  72
  73                 _ => false,
  74             }
  75         };
  76         let result = result || self.is_static(super_region);
  77         debug!(
  78             "is_subregion_of(sub_region={:?}, super_region={:?}) = {:?}",
  79             sub_region, super_region, result
  80         );
  81         result
  82     }
  83
  84     /// Determines whether this free region is required to be `'static`.
  85     fn is_static(&self, super_region: ty::Region<'tcx>) -> bool {
  86         debug!("is_static(super_region={:?})", super_region);
  87         match *super_region {
  88             ty::ReStatic => true,
  89             ty::ReEarlyBound(_) | ty::ReFree(_) => {
  90                 let re_static = self.tcx.mk_region(ty::ReStatic);
  91                 self.free_regions.sub_free_regions(&re_static, &super_region)
  92             }
  93             _ => false,
  94         }
  95     }
  96
  97     pub fn lub_free_regions(&self, r_a: Region<'tcx>, r_b: Region<'tcx>) -> Region<'tcx> {
  98         self.free_regions.lub_free_regions(self.tcx, r_a, r_b)
  99     }
 100 }