src/librustc_traits/normalize_erasing_regions.rs

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