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 rustc_span::source_map::DUMMY_SP;
   8
   9 crate fn provide(p: &mut Providers<'_>) {
  10     *p = Providers { evaluate_obligation, ..*p };
  11 }
  12
  13 fn evaluate_obligation<'tcx>(
  14     tcx: TyCtxt<'tcx>,
  15     canonical_goal: CanonicalPredicateGoal<'tcx>,
  16 ) -> Result<EvaluationResult, OverflowError> {
  17     debug!("evaluate_obligation(canonical_goal={:#?})", canonical_goal);
  18     tcx.infer_ctxt().enter_with_canonical(
  19         DUMMY_SP,
  20         &canonical_goal,
  21         |ref infcx, goal, _canonical_inference_vars| {
  22             debug!("evaluate_obligation: goal={:#?}", goal);
  23             let ParamEnvAnd { param_env, value: predicate } = goal;
  24
  25             let mut selcx = SelectionContext::with_query_mode(&infcx, TraitQueryMode::Canonical);
  26             let obligation = Obligation::new(ObligationCause::dummy(), param_env, predicate);
  27
  28             selcx.evaluate_root_obligation(&obligation)
  29         },
  30     )
  31 }