src/librustc_traits/normalize_erasing_regions.rs

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