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>,
  18     canonical_goal: CanonicalPredicateGoal<'tcx>,
  19 ) -> Result<EvaluationResult, OverflowError> {
  20     debug!("evaluate_obligation(canonical_goal={:#?})", canonical_goal);
  21     tcx.infer_ctxt().enter_with_canonical(
  22         DUMMY_SP,
  23         &canonical_goal,
  24         |ref infcx, goal, _canonical_inference_vars| {
  25             debug!("evaluate_obligation: goal={:#?}", goal);
  26             let ParamEnvAnd {
  27                 param_env,
  28                 value: predicate,
  29             } = goal;
  30
  31             let mut selcx = SelectionContext::with_query_mode(&infcx, TraitQueryMode::Canonical);
  32             let obligation = Obligation::new(ObligationCause::dummy(), param_env, predicate);
  33
  34             selcx.evaluate_root_obligation(&obligation)
  35         },
  36     )
  37 }