1 files changed, 40 insertions, 0 deletions
diff --git a/compiler/rustc_infer/src/infer/projection.rs b/compiler/rustc_infer/src/infer/projection.rs
new file mode 100644
index 000000000..b45a6514d
--- /dev/null
+++ b/compiler/rustc_infer/src/infer/projection.rs
@@ -0,0 +1,40 @@
+use rustc_middle::traits::ObligationCause;
+use rustc_middle::ty::{self, ToPredicate, Ty};
+
+use crate::traits::{Obligation, PredicateObligation};
+
+use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use super::InferCtxt;
+
+impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
+    /// Instead of normalizing an associated type projection,
+    /// this function generates an inference variable and registers
+    /// an obligation that this inference variable must be the result
+    /// of the given projection. This allows us to proceed with projections
+    /// while they cannot be resolved yet due to missing information or
+    /// simply due to the lack of access to the trait resolution machinery.
+    pub fn infer_projection(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        projection_ty: ty::ProjectionTy<'tcx>,
+        cause: ObligationCause<'tcx>,
+        recursion_depth: usize,
+        obligations: &mut Vec<PredicateObligation<'tcx>>,
+    ) -> Ty<'tcx> {
+        let def_id = projection_ty.item_def_id;
+        let ty_var = self.next_ty_var(TypeVariableOrigin {
+            kind: TypeVariableOriginKind::NormalizeProjectionType,
+            span: self.tcx.def_span(def_id),
+        });
+        let projection =
+            ty::Binder::dummy(ty::ProjectionPredicate { projection_ty, term: ty_var.into() });
+        let obligation = Obligation::with_depth(
+            cause,
+            recursion_depth,
+            param_env,
+            projection.to_predicate(self.tcx),
+        );
+        obligations.push(obligation);
+        ty_var
+    }
+}