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 crate fn provide(p: &mut Providers) {
  10     *p = Providers {
  11         normalize_generic_arg_after_erasing_regions: |tcx, goal| {
  12             debug!("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             normalize_after_erasing_regions(tcx, goal)
  19         },
  20         normalize_mir_const_after_erasing_regions: |tcx, goal| {
  21             normalize_after_erasing_regions(tcx, goal)
  22         },
  23         try_normalize_generic_arg_after_erasing_regions: |tcx, goal| {
  24             debug!("try_normalize_generic_arg_after_erasing_regions(goal={:#?}", goal);
  25
  26             try_normalize_after_erasing_regions(tcx, goal)
  27         },
  28         try_normalize_mir_const_after_erasing_regions: |tcx, goal| {
  29             try_normalize_after_erasing_regions(tcx, goal)
  30         },
  31         ..*p
  32     };
  33 }
  34
  35 #[instrument(level = "debug", skip(tcx))]
  36 fn normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq + Copy>(
  37     tcx: TyCtxt<'tcx>,
  38     goal: ParamEnvAnd<'tcx, T>,
  39 ) -> T {
  40     let ParamEnvAnd { param_env, value } = goal;
  41     tcx.infer_ctxt().enter(|infcx| {
  42         let cause = ObligationCause::dummy();
  43         match infcx.at(&cause, param_env).normalize(value) {
  44             Ok(Normalized { value: normalized_value, obligations: normalized_obligations }) => {
  45                 // We don't care about the `obligations`; they are
  46                 // always only region relations, and we are about to
  47                 // erase those anyway:
  48                 debug_assert_eq!(
  49                     normalized_obligations.iter().find(|p| not_outlives_predicate(&p.predicate)),
  50                     None,
  51                 );
  52
  53                 let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
  54                 // It's unclear when `resolve_vars` would have an effect in a
  55                 // fresh `InferCtxt`. If this assert does trigger, it will give
  56                 // us a test case.
  57                 debug_assert_eq!(normalized_value, resolved_value);
  58                 let erased = infcx.tcx.erase_regions(resolved_value);
  59                 debug_assert!(!erased.needs_infer(), "{:?}", erased);
  60                 erased
  61             }
  62             Err(NoSolution) => bug!("could not fully normalize `{:?}`", value),
  63         }
  64     })
  65 }
  66
  67 #[instrument(level = "debug", skip(tcx))]
  68 fn try_normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq + Copy>(
  69     tcx: TyCtxt<'tcx>,
  70     goal: ParamEnvAnd<'tcx, T>,
  71 ) -> Result<T, NoSolution> {
  72     let ParamEnvAnd { param_env, value } = goal;
  73     tcx.infer_ctxt().enter(|infcx| {
  74         let cause = ObligationCause::dummy();
  75         match infcx.at(&cause, param_env).normalize(value) {
  76             Ok(Normalized { value: normalized_value, obligations: normalized_obligations }) => {
  77                 // We don't care about the `obligations`; they are
  78                 // always only region relations, and we are about to
  79                 // erase those anyway:
  80                 debug_assert_eq!(
  81                     normalized_obligations.iter().find(|p| not_outlives_predicate(&p.predicate)),
  82                     None,
  83                 );
  84
  85                 let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
  86                 // It's unclear when `resolve_vars` would have an effect in a
  87                 // fresh `InferCtxt`. If this assert does trigger, it will give
  88                 // us a test case.
  89                 debug_assert_eq!(normalized_value, resolved_value);
  90                 let erased = infcx.tcx.erase_regions(resolved_value);
  91                 debug_assert!(!erased.needs_infer(), "{:?}", erased);
  92                 Ok(erased)
  93             }
  94             Err(NoSolution) => Err(NoSolution),
  95         }
  96     })
  97 }
  98
  99 fn not_outlives_predicate(p: &ty::Predicate<'tcx>) -> bool {
 100     match p.kind().skip_binder() {
 101         ty::PredicateKind::RegionOutlives(..) | ty::PredicateKind::TypeOutlives(..) => false,
 102         ty::PredicateKind::Trait(..)
 103         | ty::PredicateKind::Projection(..)
 104         | ty::PredicateKind::WellFormed(..)
 105         | ty::PredicateKind::ObjectSafe(..)
 106         | ty::PredicateKind::ClosureKind(..)
 107         | ty::PredicateKind::Subtype(..)
 108         | ty::PredicateKind::Coerce(..)
 109         | ty::PredicateKind::ConstEvaluatable(..)
 110         | ty::PredicateKind::ConstEquate(..)
 111         | ty::PredicateKind::TypeWellFormedFromEnv(..) => true,
 112     }
 113 }