compiler/rustc_infer/src/infer/projection.rs

   1 use rustc_middle::traits::ObligationCause;
   2 use rustc_middle::ty::{self, ToPredicate, Ty};
   3
   4 use crate::traits::{Obligation, PredicateObligation};
   5
   6 use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
   7 use super::InferCtxt;
   8
   9 impl<'tcx> InferCtxt<'tcx> {
  10     /// Instead of normalizing an associated type projection,
  11     /// this function generates an inference variable and registers
  12     /// an obligation that this inference variable must be the result
  13     /// of the given projection. This allows us to proceed with projections
  14     /// while they cannot be resolved yet due to missing information or
  15     /// simply due to the lack of access to the trait resolution machinery.
  16     pub fn infer_projection(
  17         &self,
  18         param_env: ty::ParamEnv<'tcx>,
  19         projection_ty: ty::ProjectionTy<'tcx>,
  20         cause: ObligationCause<'tcx>,
  21         recursion_depth: usize,
  22         obligations: &mut Vec<PredicateObligation<'tcx>>,
  23     ) -> Ty<'tcx> {
  24         let def_id = projection_ty.item_def_id;
  25         let ty_var = self.next_ty_var(TypeVariableOrigin {
  26             kind: TypeVariableOriginKind::NormalizeProjectionType,
  27             span: self.tcx.def_span(def_id),
  28         });
  29         let projection =
  30             ty::Binder::dummy(ty::ProjectionPredicate { projection_ty, term: ty_var.into() });
  31         let obligation = Obligation::with_depth(
  32             cause,
  33             recursion_depth,
  34             param_env,
  35             projection.to_predicate(self.tcx),
  36         );
  37         obligations.push(obligation);
  38         ty_var
  39     }
  40 }