Auto merge of #118947 - Bryanskiy:delegStep1, r=petrochenkov,lcnr

Delegation implementation: step 1

See #118212 for more details.

r? `@petrochenkov`

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>,
@@ -3104,14 +3114,20 @@ 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 {
     pub fn article(&self) -> &'static str {
         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),
         })
     }

compiler/rustc_ast/src/mut_visit.rs

@@ -1117,6 +1117,14 @@ pub fn noop_visit_item_kind<T: MutVisitor>(kind: &mut ItemKind, vis: &mut T) {
         }
         ItemKind::MacCall(m) => vis.visit_mac_call(m),
         ItemKind::MacroDef(def) => vis.visit_macro_def(def),
+        ItemKind::Delegation(box Delegation { id, qself, path, body }) => {
+            vis.visit_id(id);
+            vis.visit_qself(qself);
+            vis.visit_path(path);
+            if let Some(body) = body {
+                vis.visit_block(body);
+            }
+        }
     }
 }
 
@@ -1155,6 +1163,14 @@ pub fn noop_flat_map_assoc_item<T: MutVisitor>(
             visit_opt(ty, |ty| visitor.visit_ty(ty));
         }
         AssocItemKind::MacCall(mac) => visitor.visit_mac_call(mac),
+        AssocItemKind::Delegation(box Delegation { id, qself, path, body }) => {
+            visitor.visit_id(id);
+            visitor.visit_qself(qself);
+            visitor.visit_path(path);
+            if let Some(body) = body {
+                visitor.visit_block(body);
+            }
+        }
     }
     visitor.visit_span(span);
     visit_lazy_tts(tokens, visitor);

compiler/rustc_ast/src/visit.rs

@@ -375,6 +375,15 @@ pub fn walk_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a Item) {
         }
         ItemKind::MacCall(mac) => visitor.visit_mac_call(mac),
         ItemKind::MacroDef(ts) => visitor.visit_mac_def(ts, item.id),
+        ItemKind::Delegation(box Delegation { id: _, qself, path, body }) => {
+            if let Some(qself) = qself {
+                visitor.visit_ty(&qself.ty);
+            }
+            walk_path(visitor, path);
+            if let Some(body) = body {
+                visitor.visit_block(body);
+            }
+        }
     }
     walk_list!(visitor, visit_attribute, &item.attrs);
 }
@@ -704,6 +713,15 @@ pub fn walk_assoc_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a AssocItem,
         AssocItemKind::MacCall(mac) => {
             visitor.visit_mac_call(mac);
         }
+        AssocItemKind::Delegation(box Delegation { id: _, qself, path, body }) => {
+            if let Some(qself) = qself {
+                visitor.visit_ty(&qself.ty);
+            }
+            walk_path(visitor, path);
+            if let Some(body) = body {
+                visitor.visit_block(body);
+            }
+        }
     }
 }