src/librustc_traits/evaluate_obligation.rs

   1 use rustc::traits::query::CanonicalPredicateGoal;
   2 use rustc::traits::{
   3     EvaluationResult, Obligation, ObligationCause, OverflowError, SelectionContext, TraitQueryMode,
   4 };
   5 use rustc::ty::query::Providers;
   6 use rustc::ty::{ParamEnvAnd, TyCtxt};
   7 use syntax::source_map::DUMMY_SP;
   8
   9 crate fn provide(p: &mut Providers<'_>) {
  10     *p = Providers {
  11         evaluate_obligation,
  12         ..*p
  13     };
  14 }
  15
  16 fn evaluate_obligation<'tcx>(
  17     tcx: TyCtxt<'tcx, 'tcx>,
  18     canonical_goal: CanonicalPredicateGoal<'tcx>,
  19 ) -> Result<EvaluationResult, OverflowError> {
  20     tcx.infer_ctxt().enter_with_canonical(
  21         DUMMY_SP,
  22         &canonical_goal,
  23         |ref infcx, goal, _canonical_inference_vars| {
  24             let ParamEnvAnd {
  25                 param_env,
  26                 value: predicate,
  27             } = goal;
  28
  29             let mut selcx = SelectionContext::with_query_mode(&infcx, TraitQueryMode::Canonical);
  30             let obligation = Obligation::new(ObligationCause::dummy(), param_env, predicate);
  31
  32             selcx.evaluate_obligation_recursively(&obligation)
  33         },
  34     )
  35 }