src/librustc_traits/evaluate_obligation.rs

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