compiler/rustc_traits/src/normalize_erasing_regions.rs

   1 use rustc_infer::infer::TyCtxtInferExt;
   2 use rustc_middle::traits::query::NoSolution;
   3 use rustc_middle::ty::query::Providers;
   4 use rustc_middle::ty::{self, ParamEnvAnd, TyCtxt, TypeFoldable};
   5 use rustc_trait_selection::traits::query::normalize::AtExt;
   6 use rustc_trait_selection::traits::{Normalized, ObligationCause};
   7 use std::sync::atomic::Ordering;
   8
   9 pub(crate) fn provide(p: &mut Providers) {
  10     *p = Providers {
  11         try_normalize_generic_arg_after_erasing_regions: |tcx, goal| {
  12             debug!("try_normalize_generic_arg_after_erasing_regions(goal={:#?}", goal);
  13
  14             tcx.sess
  15                 .perf_stats
  16                 .normalize_generic_arg_after_erasing_regions
  17                 .fetch_add(1, Ordering::Relaxed);
  18
  19             try_normalize_after_erasing_regions(tcx, goal)
  20         },
  21         ..*p
  22     };
  23 }
  24
  25 fn try_normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq + Copy>(
  26     tcx: TyCtxt<'tcx>,
  27     goal: ParamEnvAnd<'tcx, T>,
  28 ) -> Result<T, NoSolution> {
  29     let ParamEnvAnd { param_env, value } = goal;
  30     let infcx = tcx.infer_ctxt().build();
  31     let cause = ObligationCause::dummy();
  32     match infcx.at(&cause, param_env).normalize(value) {
  33         Ok(Normalized { value: normalized_value, obligations: normalized_obligations }) => {
  34             // We don't care about the `obligations`; they are
  35             // always only region relations, and we are about to
  36             // erase those anyway:
  37             debug_assert_eq!(
  38                 normalized_obligations.iter().find(|p| not_outlives_predicate(p.predicate)),
  39                 None,
  40             );
  41
  42             let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
  43             // It's unclear when `resolve_vars` would have an effect in a
  44             // fresh `InferCtxt`. If this assert does trigger, it will give
  45             // us a test case.
  46             debug_assert_eq!(normalized_value, resolved_value);
  47             let erased = infcx.tcx.erase_regions(resolved_value);
  48             debug_assert!(!erased.needs_infer(), "{:?}", erased);
  49             Ok(erased)
  50         }
  51         Err(NoSolution) => Err(NoSolution),
  52     }
  53 }
  54
  55 fn not_outlives_predicate<'tcx>(p: ty::Predicate<'tcx>) -> bool {
  56     match p.kind().skip_binder() {
  57         ty::PredicateKind::RegionOutlives(..) | ty::PredicateKind::TypeOutlives(..) => false,
  58         ty::PredicateKind::Trait(..)
  59         | ty::PredicateKind::Projection(..)
  60         | ty::PredicateKind::WellFormed(..)
  61         | ty::PredicateKind::ObjectSafe(..)
  62         | ty::PredicateKind::ClosureKind(..)
  63         | ty::PredicateKind::Subtype(..)
  64         | ty::PredicateKind::Coerce(..)
  65         | ty::PredicateKind::ConstEvaluatable(..)
  66         | ty::PredicateKind::ConstEquate(..)
  67         | ty::PredicateKind::TypeWellFormedFromEnv(..) => true,
  68     }
  69 }