delegation: impl step 1

compiler/rustc_ast/src/ast.rs

@@ -2978,6 +2978,14 @@ pub struct Fn {
     pub body: Option<P<Block>>,
 }
 
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub struct Delegation {
+    pub id: NodeId,
+    pub path: (Option<P<QSelf>>, Path),
+    pub target_expr: Option<P<Expr>>,
+    pub span: Span,
+}
+
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct StaticItem {
     pub ty: P<Ty>,
@@ -3063,14 +3071,20 @@ 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",
         }
     }
@@ -3094,6 +3108,7 @@ impl ItemKind {
             ItemKind::MacCall(..) => "item macro invocation",
             ItemKind::MacroDef(..) => "macro definition",
             ItemKind::Impl { .. } => "implementation",
+            ItemKind::Delegation(..) => "delegation",
         }
     }
 
@@ -3135,6 +3150,8 @@ pub enum AssocItemKind {
     Type(Box<TyAlias>),
     /// A macro expanding to associated items.
     MacCall(P<MacCall>),
+    /// An associated delegation item.
+    Delegation(Box<Delegation>),
 }
 
 impl AssocItemKind {
@@ -3143,7 +3160,7 @@ 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,
         }
     }
 }
@@ -3155,6 +3172,7 @@ 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),
         }
     }
 }
@@ -3168,6 +3186,7 @@ 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/ast_traits.rs

@@ -5,7 +5,7 @@
 use crate::ptr::P;
 use crate::token::Nonterminal;
 use crate::tokenstream::LazyAttrTokenStream;
-use crate::{Arm, Crate, ExprField, FieldDef, GenericParam, Param, PatField, Variant};
+use crate::{Arm, Crate, Delegation, ExprField, FieldDef, GenericParam, Param, PatField, Variant};
 use crate::{AssocItem, Expr, ForeignItem, Item, NodeId};
 use crate::{AttrItem, AttrKind, Block, Pat, Path, Ty, Visibility};
 use crate::{AttrVec, Attribute, Stmt, StmtKind};
@@ -80,6 +80,7 @@ impl_has_node_id!(
     Stmt,
     Ty,
     Variant,
+    Delegation
 );
 
 impl<T: AstDeref<Target: HasNodeId>> HasNodeId for T {
@@ -108,7 +109,19 @@ macro_rules! impl_has_span {
     };
 }
 
-impl_has_span!(AssocItem, Block, Expr, ForeignItem, Item, Pat, Path, Stmt, Ty, Visibility);
+impl_has_span!(
+    AssocItem,
+    Block,
+    Expr,
+    ForeignItem,
+    Item,
+    Pat,
+    Path,
+    Stmt,
+    Ty,
+    Visibility,
+    Delegation
+);
 
 impl<T: AstDeref<Target: HasSpan>> HasSpan for T {
     fn span(&self) -> Span {
@@ -159,7 +172,7 @@ macro_rules! impl_has_tokens_none {
 }
 
 impl_has_tokens!(AssocItem, AttrItem, Block, Expr, ForeignItem, Item, Pat, Path, Ty, Visibility);
-impl_has_tokens_none!(Arm, ExprField, FieldDef, GenericParam, Param, PatField, Variant);
+impl_has_tokens_none!(Arm, ExprField, FieldDef, GenericParam, Param, PatField, Variant, Delegation);
 
 impl<T: AstDeref<Target: HasTokens>> HasTokens for T {
     fn tokens(&self) -> Option<&LazyAttrTokenStream> {

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) => {
+            vis.visit_id(&mut delegation.id);
+            vis.visit_qself(&mut delegation.path.0);
+            vis.visit_path(&mut delegation.path.1);
+            if let Some(target_expr) = &mut delegation.target_expr {
+                vis.visit_expr(target_expr);
+            }
+        }
     }
 }
 
@@ -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) => {
+            visitor.visit_id(&mut delegation.id);
+            visitor.visit_qself(&mut delegation.path.0);
+            visitor.visit_path(&mut delegation.path.1);
+            if let Some(target_expr) = &mut delegation.target_expr {
+                visitor.visit_expr(target_expr);
+            }
+        }
     }
     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) => {
+            if let Some(qself) = &delegation.path.0 {
+                visitor.visit_ty(&qself.ty);
+            }
+            walk_path(visitor, &delegation.path.1);
+            if let Some(target_expr) = &delegation.target_expr {
+                visitor.visit_expr(target_expr);
+            }
+        }
     }
     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) => {
+            if let Some(qself) = &delegation.path.0 {
+                visitor.visit_ty(&qself.ty);
+            }
+            walk_path(visitor, &delegation.path.1);
+            if let Some(target_expr) = &delegation.target_expr {
+                visitor.visit_expr(target_expr);
+            }
+        }
     }
 }