src/librustc_traits/evaluate_obligation.rs

   1 // Copyright 2018 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::{EvaluationResult, Obligation, ObligationCause,
  12                     OverflowError, SelectionContext, TraitQueryMode};
  13 use rustc::traits::query::CanonicalPredicateGoal;
  14 use rustc::ty::query::Providers;
  15 use rustc::ty::{ParamEnvAnd, TyCtxt};
  16 use syntax::codemap::DUMMY_SP;
  17
  18 crate fn provide(p: &mut Providers) {
  19     *p = Providers {
  20         evaluate_obligation,
  21         ..*p
  22     };
  23 }
  24
  25 fn evaluate_obligation<'tcx>(
  26     tcx: TyCtxt<'_, 'tcx, 'tcx>,
  27     goal: CanonicalPredicateGoal<'tcx>,
  28 ) -> Result<EvaluationResult, OverflowError> {
  29     tcx.infer_ctxt().enter(|ref infcx| {
  30         let (
  31             ParamEnvAnd {
  32                 param_env,
  33                 value: predicate,
  34             },
  35             _canonical_inference_vars,
  36         ) = infcx.instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &goal);
  37
  38         let mut selcx = SelectionContext::with_query_mode(&infcx, TraitQueryMode::Canonical);
  39         let obligation = Obligation::new(ObligationCause::dummy(), param_env, predicate);
  40
  41         selcx.evaluate_obligation_recursively(&obligation)
  42     })
  43 }