src/librustc_traits/normalize_erasing_regions.rs

   1 use rustc::traits::{Normalized, ObligationCause};
   2 use rustc::traits::query::NoSolution;
   3 use rustc::ty::query::Providers;
   4 use rustc::ty::{self, ParamEnvAnd, Ty, TyCtxt};
   5 use std::sync::atomic::Ordering;
   6
   7 crate fn provide(p: &mut Providers<'_>) {
   8     *p = Providers {
   9         normalize_ty_after_erasing_regions,
  10         ..*p
  11     };
  12 }
  13
  14 fn normalize_ty_after_erasing_regions<'tcx>(
  15     tcx: TyCtxt<'_, 'tcx, 'tcx>,
  16     goal: ParamEnvAnd<'tcx, Ty<'tcx>>,
  17 ) -> Ty<'tcx> {
  18     debug!("normalize_ty_after_erasing_regions(goal={:#?})", goal);
  19
  20     let ParamEnvAnd { param_env, value } = goal;
  21     tcx.sess.perf_stats.normalize_ty_after_erasing_regions.fetch_add(1, Ordering::Relaxed);
  22     tcx.infer_ctxt().enter(|infcx| {
  23         let cause = ObligationCause::dummy();
  24         match infcx.at(&cause, param_env).normalize(&value) {
  25             Ok(Normalized {
  26                 value: normalized_value,
  27                 obligations: normalized_obligations,
  28             }) => {
  29                 // We don't care about the `obligations`; they are
  30                 // always only region relations, and we are about to
  31                 // erase those anyway:
  32                 debug_assert_eq!(
  33                     normalized_obligations
  34                         .iter()
  35                         .find(|p| not_outlives_predicate(&p.predicate)),
  36                     None,
  37                 );
  38
  39                 let normalized_value = infcx.resolve_vars_if_possible(&normalized_value);
  40                 let normalized_value = infcx.tcx.erase_regions(&normalized_value);
  41                 tcx.lift_to_global(&normalized_value).unwrap()
  42             }
  43             Err(NoSolution) => bug!("could not fully normalize `{:?}`", value),
  44         }
  45     })
  46 }
  47
  48 fn not_outlives_predicate(p: &ty::Predicate<'_>) -> bool {
  49     match p {
  50         ty::Predicate::RegionOutlives(..) | ty::Predicate::TypeOutlives(..) => false,
  51         ty::Predicate::Trait(..)
  52         | ty::Predicate::Projection(..)
  53         | ty::Predicate::WellFormed(..)
  54         | ty::Predicate::ObjectSafe(..)
  55         | ty::Predicate::ClosureKind(..)
  56         | ty::Predicate::Subtype(..)
  57         | ty::Predicate::ConstEvaluatable(..) => true,
  58     }
  59 }