compiler/rustc_traits/src/evaluate_obligation.rs

   1 use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
   2 use rustc_middle::ty::query::Providers;
   3 use rustc_middle::ty::{ParamEnvAnd, TyCtxt};
   4 use rustc_span::source_map::DUMMY_SP;
   5 use rustc_trait_selection::traits::query::CanonicalPredicateGoal;
   6 use rustc_trait_selection::traits::{
   7     EvaluationResult, Obligation, ObligationCause, OverflowError, SelectionContext, TraitQueryMode,
   8 };
   9
  10 pub(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     // HACK This bubble is required for this tests to pass:
  20     // impl-trait/issue99642.rs
  21     let (ref infcx, goal, _canonical_inference_vars) = tcx
  22         .infer_ctxt()
  23         .with_opaque_type_inference(DefiningAnchor::Bubble)
  24         .build_with_canonical(DUMMY_SP, &canonical_goal);
  25     debug!("evaluate_obligation: goal={:#?}", goal);
  26     let ParamEnvAnd { param_env, value: predicate } = goal;
  27
  28     let mut selcx = SelectionContext::with_query_mode(&infcx, TraitQueryMode::Canonical);
  29     let obligation = Obligation::new(ObligationCause::dummy(), param_env, predicate);
  30
  31     selcx.evaluate_root_obligation(&obligation)
  32 }