Delegation implementation: step 1

compiler/rustc_ast/src/ast.rs

@@ -2873,6 +2873,7 @@ impl Item {
             | ItemKind::ForeignMod(_)
             | ItemKind::GlobalAsm(_)
             | ItemKind::MacCall(_)
+            | ItemKind::Delegation(_)
             | ItemKind::MacroDef(_) => None,
             ItemKind::Static(_) => None,
             ItemKind::Const(i) => Some(&i.generics),
@@ -3019,6 +3020,15 @@ pub struct Fn {
     pub body: Option<P<Block>>,
 }
 
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub struct Delegation {
+    /// Path resolution id.
+    pub id: NodeId,
+    pub qself: Option<P<QSelf>>,
+    pub path: Path,
+    pub body: Option<P<Block>>,
+}
+
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct StaticItem {
     pub ty: P<Ty>,
@@ -3104,6 +3114,11 @@ pub enum ItemKind {
 
     /// A macro definition.
     MacroDef(MacroDef),
+
+    /// A delegation item (`reuse`).
+    ///
+    /// E.g. `reuse <Type as Trait>::name { target_expr_template }`.
+    Delegation(Box<Delegation>),
 }
 
 impl ItemKind {
@@ -3111,7 +3126,8 @@ impl ItemKind {
         use ItemKind::*;
         match self {
             Use(..) | Static(..) | Const(..) | Fn(..) | Mod(..) | GlobalAsm(..) | TyAlias(..)
-            | Struct(..) | Union(..) | Trait(..) | TraitAlias(..) | MacroDef(..) => "a",
+            | Struct(..) | Union(..) | Trait(..) | TraitAlias(..) | MacroDef(..)
+            | Delegation(..) => "a",
             ExternCrate(..) | ForeignMod(..) | MacCall(..) | Enum(..) | Impl { .. } => "an",
         }
     }
@@ -3135,6 +3151,7 @@ impl ItemKind {
             ItemKind::MacCall(..) => "item macro invocation",
             ItemKind::MacroDef(..) => "macro definition",
             ItemKind::Impl { .. } => "implementation",
+            ItemKind::Delegation(..) => "delegated function",
         }
     }
 
@@ -3176,6 +3193,8 @@ pub enum AssocItemKind {
     Type(Box<TyAlias>),
     /// A macro expanding to associated items.
     MacCall(P<MacCall>),
+    /// An associated delegation item.
+    Delegation(Box<Delegation>),
 }
 
 impl AssocItemKind {
@@ -3184,7 +3203,7 @@ impl AssocItemKind {
             Self::Const(box ConstItem { defaultness, .. })
             | Self::Fn(box Fn { defaultness, .. })
             | Self::Type(box TyAlias { defaultness, .. }) => defaultness,
-            Self::MacCall(..) => Defaultness::Final,
+            Self::MacCall(..) | Self::Delegation(..) => Defaultness::Final,
         }
     }
 }
@@ -3196,6 +3215,7 @@ impl From<AssocItemKind> for ItemKind {
             AssocItemKind::Fn(fn_kind) => ItemKind::Fn(fn_kind),
             AssocItemKind::Type(ty_alias_kind) => ItemKind::TyAlias(ty_alias_kind),
             AssocItemKind::MacCall(a) => ItemKind::MacCall(a),
+            AssocItemKind::Delegation(delegation) => ItemKind::Delegation(delegation),
         }
     }
 }
@@ -3209,6 +3229,7 @@ impl TryFrom<ItemKind> for AssocItemKind {
             ItemKind::Fn(fn_kind) => AssocItemKind::Fn(fn_kind),
             ItemKind::TyAlias(ty_kind) => AssocItemKind::Type(ty_kind),
             ItemKind::MacCall(a) => AssocItemKind::MacCall(a),
+            ItemKind::Delegation(d) => AssocItemKind::Delegation(d),
             _ => return Err(item_kind),
         })
     }