src/librustc_traits/normalize_erasing_regions.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::traits::{Normalized, ObligationCause};
  12 use rustc::traits::query::NoSolution;
  13 use rustc::ty::query::Providers;
  14 use rustc::ty::{self, ParamEnvAnd, Ty, TyCtxt};
  15 use std::sync::atomic::Ordering;
  16
  17 crate fn provide(p: &mut Providers) {
  18     *p = Providers {
  19         normalize_ty_after_erasing_regions,
  20         ..*p
  21     };
  22 }
  23
  24 fn normalize_ty_after_erasing_regions<'tcx>(
  25     tcx: TyCtxt<'_, 'tcx, 'tcx>,
  26     goal: ParamEnvAnd<'tcx, Ty<'tcx>>,
  27 ) -> Ty<'tcx> {
  28     debug!("normalize_ty_after_erasing_regions(goal={:#?})", goal);
  29
  30     let ParamEnvAnd { param_env, value } = goal;
  31     tcx.sess.perf_stats.normalize_ty_after_erasing_regions.fetch_add(1, Ordering::Relaxed);
  32     tcx.infer_ctxt().enter(|infcx| {
  33         let cause = ObligationCause::dummy();
  34         match infcx.at(&cause, param_env).normalize(&value) {
  35             Ok(Normalized {
  36                 value: normalized_value,
  37                 obligations: normalized_obligations,
  38             }) => {
  39                 // We don't care about the `obligations`; they are
  40                 // always only region relations, and we are about to
  41                 // erase those anyway:
  42                 debug_assert_eq!(
  43                     normalized_obligations
  44                         .iter()
  45                         .find(|p| not_outlives_predicate(&p.predicate)),
  46                     None,
  47                 );
  48
  49                 let normalized_value = infcx.resolve_type_vars_if_possible(&normalized_value);
  50                 let normalized_value = infcx.tcx.erase_regions(&normalized_value);
  51                 tcx.lift_to_global(&normalized_value).unwrap()
  52             }
  53             Err(NoSolution) => bug!("could not fully normalize `{:?}`", value),
  54         }
  55     })
  56 }
  57
  58 fn not_outlives_predicate(p: &ty::Predicate<'_>) -> bool {
  59     match p {
  60         ty::Predicate::RegionOutlives(..) | ty::Predicate::TypeOutlives(..) => false,
  61         ty::Predicate::Trait(..)
  62         | ty::Predicate::Projection(..)
  63         | ty::Predicate::WellFormed(..)
  64         | ty::Predicate::ObjectSafe(..)
  65         | ty::Predicate::ClosureKind(..)
  66         | ty::Predicate::Subtype(..)
  67         | ty::Predicate::ConstEvaluatable(..) => true,
  68     }
  69 }