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