Delegation implementation: step 1

compiler/rustc_hir/src/hir.rs

@@ -2571,9 +2571,17 @@ pub enum OpaqueTyOrigin {
     },
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable_Generic)]
+pub enum InferDelegationKind {
+    Input(usize),
+    Output,
+}
+
 /// The various kinds of types recognized by the compiler.
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub enum TyKind<'hir> {
+    /// Actual type should be inherited from `DefId` signature
+    InferDelegation(DefId, InferDelegationKind),
     /// A variable length slice (i.e., `[T]`).
     Slice(&'hir Ty<'hir>),
     /// A fixed length array (i.e., `[T; n]`).

compiler/rustc_hir/src/intravisit.rs

@@ -856,7 +856,7 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) {
             visitor.visit_lifetime(lifetime);
         }
         TyKind::Typeof(ref expression) => visitor.visit_anon_const(expression),
-        TyKind::Infer | TyKind::Err(_) => {}
+        TyKind::Infer | TyKind::InferDelegation(..) | TyKind::Err(_) => {}
     }
 }