delegation: Implement list delegation

```rust
reuse prefix::{a, b, c}
```

Author: petrochenkov

compiler/rustc_ast/src/ast.rs

@@ -2961,6 +2961,7 @@ impl Item {
  | ItemKind::GlobalAsm(_)
  | ItemKind::MacCall(_)
  | ItemKind::Delegation(_)
+ | ItemKind::DelegationMac(_)
  | ItemKind::MacroDef(_) => None,
 ItemKind::Static(_) => None,
 ItemKind::Const(i) => Some(&i.generics),
@@ -3123,8 +3124,16 @@ pub struct Delegation {
 /// Path resolution id.
 pubid:NodeId,
 pubqself:Option<P<QSelf>>,
-pubrename:Option<Ident>,
 pubpath:Path,
+pubrename:Option<Ident>,
+pubbody:Option<P<Block>>,
+}
+
+#[derive(Clone,Encodable,Decodable,Debug)]
+pubstructDelegationMac{
+pubqself:Option<P<QSelf>>,
+pubprefix:Path,
+pubsuffixes:ThinVec<(Ident,Option<Ident>)>,
 pubbody:Option<P<Block>>,
 }
 
@@ -3243,10 +3252,13 @@ pub enum ItemKind {
 /// A macro definition.
 MacroDef(MacroDef),
 
-/// A delegation item (`reuse`).
+/// A single delegation item (`reuse`).
 ///
 /// E.g. `reuse <Type as Trait>::name { target_expr_template }`.
 Delegation(Box<Delegation>),
+/// A list delegation item (`reuse prefix::{a, b, c}`).
+/// Treated similarly to a macro call and expanded early.
+DelegationMac(Box<DelegationMac>),
 }
 
 implItemKind{
@@ -3255,7 +3267,7 @@ impl ItemKind {
 matchself{
 Use(..) | Static(..) | Const(..) | Fn(..) | Mod(..) | GlobalAsm(..) | TyAlias(..)
  | Struct(..) | Union(..) | Trait(..) | TraitAlias(..) | MacroDef(..)
- | Delegation(..) => "a",
+ | Delegation(..)| DelegationMac(..)=> "a",
 ExternCrate(..) | ForeignMod(..) | MacCall(..) | Enum(..) | Impl{ .. } => "an",
 }
 }
@@ -3280,6 +3292,7 @@ impl ItemKind {
 ItemKind::MacroDef(..) => "macro definition",
 ItemKind::Impl{ .. } => "implementation",
 ItemKind::Delegation(..) => "delegated function",
+ItemKind::DelegationMac(..) => "delegation",
 }
 }
 
@@ -3323,6 +3336,8 @@ pub enum AssocItemKind {
 MacCall(P<MacCall>),
 /// An associated delegation item.
 Delegation(Box<Delegation>),
+/// An associated delegation item list.
+DelegationMac(Box<DelegationMac>),
 }
 
 implAssocItemKind{
@@ -3331,7 +3346,9 @@ impl AssocItemKind {
 Self::Const(box ConstItem{ defaultness, .. })
  | Self::Fn(boxFn{ defaultness, .. })
  | Self::Type(box TyAlias{ defaultness, .. }) => defaultness,
-Self::MacCall(..) | Self::Delegation(..) => Defaultness::Final,
+Self::MacCall(..) | Self::Delegation(..) | Self::DelegationMac(..) => {
+Defaultness::Final
+}
 }
 }
 }
@@ -3344,6 +3361,7 @@ impl From<AssocItemKind> for ItemKind {
 AssocItemKind::Type(ty_alias_kind) => ItemKind::TyAlias(ty_alias_kind),
 AssocItemKind::MacCall(a) => ItemKind::MacCall(a),
 AssocItemKind::Delegation(delegation) => ItemKind::Delegation(delegation),
+AssocItemKind::DelegationMac(delegation) => ItemKind::DelegationMac(delegation),
 }
 }
 }
@@ -3358,6 +3376,7 @@ impl TryFrom<ItemKind> for AssocItemKind {
 ItemKind::TyAlias(ty_kind) => AssocItemKind::Type(ty_kind),
 ItemKind::MacCall(a) => AssocItemKind::MacCall(a),
 ItemKind::Delegation(d) => AssocItemKind::Delegation(d),
+ItemKind::DelegationMac(d) => AssocItemKind::DelegationMac(d),
  _ => returnErr(item_kind),
 })
 }

compiler/rustc_ast/src/mut_visit.rs

@@ -1170,6 +1170,19 @@ impl NoopVisitItemKind for ItemKind {
  vis.visit_block(body);
 }
 }
+ItemKind::DelegationMac(box DelegationMac{ qself, prefix, suffixes, body }) => {
+ vis.visit_qself(qself);
+ vis.visit_path(prefix);
+for(ident, rename)in suffixes {
+ vis.visit_ident(ident);
+ifletSome(rename) = rename {
+ vis.visit_ident(rename);
+}
+}
+ifletSome(body) = body {
+ vis.visit_block(body);
+}
+}
 }
 }
 }
@@ -1213,6 +1226,19 @@ impl NoopVisitItemKind for AssocItemKind {
  visitor.visit_block(body);
 }
 }
+AssocItemKind::DelegationMac(box DelegationMac{ qself, prefix, suffixes, body }) => {
+ visitor.visit_qself(qself);
+ visitor.visit_path(prefix);
+for(ident, rename)in suffixes {
+ visitor.visit_ident(ident);
+ifletSome(rename) = rename {
+ visitor.visit_ident(rename);
+}
+}
+ifletSome(body) = body {
+ visitor.visit_block(body);
+}
+}
 }
 }
 }

compiler/rustc_ast/src/visit.rs

@@ -403,6 +403,19 @@ impl WalkItemKind for ItemKind {
 visit_opt!(visitor, visit_ident,*rename);
 visit_opt!(visitor, visit_block, body);
 }
+ItemKind::DelegationMac(box DelegationMac{ qself, prefix, suffixes, body }) => {
+ifletSome(qself) = qself {
+try_visit!(visitor.visit_ty(&qself.ty));
+}
+try_visit!(visitor.visit_path(prefix, item.id));
+for(ident, rename)in suffixes {
+ visitor.visit_ident(*ident);
+ifletSome(rename) = rename {
+ visitor.visit_ident(*rename);
+}
+}
+visit_opt!(visitor, visit_block, body);
+}
 }
 V::Result::output()
 }
@@ -815,6 +828,19 @@ impl WalkItemKind for AssocItemKind {
 visit_opt!(visitor, visit_ident,*rename);
 visit_opt!(visitor, visit_block, body);
 }
+AssocItemKind::DelegationMac(box DelegationMac{ qself, prefix, suffixes, body }) => {
+ifletSome(qself) = qself {
+try_visit!(visitor.visit_ty(&qself.ty));
+}
+try_visit!(visitor.visit_path(prefix, item.id));
+for(ident, rename)in suffixes {
+ visitor.visit_ident(*ident);
+ifletSome(rename) = rename {
+ visitor.visit_ident(*rename);
+}
+}
+visit_opt!(visitor, visit_block, body);
+}
 }
 V::Result::output()
 }

compiler/rustc_ast_lowering/src/item.rs

@@ -460,8 +460,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
  delegation_results.body_id,
 )
 }
-ItemKind::MacCall(..) => {
-panic!("`TyMac` should have been expanded by now")
+ItemKind::MacCall(..)| ItemKind::DelegationMac(..)=> {
+panic!("macros should have been expanded by now")
 }
 }
 }
@@ -845,7 +845,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 (delegation_results.generics, item_kind,true)
 }
-AssocItemKind::MacCall(..) => panic!("macro item shouldn't exist at this point"),
+AssocItemKind::MacCall(..) | AssocItemKind::DelegationMac(..) => {
+panic!("macros should have been expanded by now")
+}
 };
 
 let item = hir::TraitItem{
@@ -869,7 +871,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
 AssocItemKind::Delegation(box delegation) => hir::AssocItemKind::Fn{
 has_self:self.delegation_has_self(i.id, delegation.id, i.span),
 },
-AssocItemKind::MacCall(..) => unimplemented!(),
+AssocItemKind::MacCall(..) | AssocItemKind::DelegationMac(..) => {
+panic!("macros should have been expanded by now")
+}
 };
 let id = hir::TraitItemId{owner_id: hir::OwnerId{def_id:self.local_def_id(i.id)}};
  hir::TraitItemRef{
@@ -964,7 +968,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
  hir::ImplItemKind::Fn(delegation_results.sig, delegation_results.body_id),
 )
 }
-AssocItemKind::MacCall(..) => panic!("`TyMac` should have been expanded by now"),
+AssocItemKind::MacCall(..) | AssocItemKind::DelegationMac(..) => {
+panic!("macros should have been expanded by now")
+}
 };
 
 let item = hir::ImplItem{
@@ -993,7 +999,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
 AssocItemKind::Delegation(box delegation) => hir::AssocItemKind::Fn{
 has_self:self.delegation_has_self(i.id, delegation.id, i.span),
 },
-AssocItemKind::MacCall(..) => unimplemented!(),
+AssocItemKind::MacCall(..) | AssocItemKind::DelegationMac(..) => {
+panic!("macros should have been expanded by now")
+}
 },
 trait_item_def_id:self
 .resolver

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -5,6 +5,7 @@ use crate::pprust::state::{AnnNode, PrintState, State, INDENT_UNIT};
 use ast::StaticItem;
 use itertools::{Itertools,Position};
 use rustc_ast as ast;
+use rustc_ast::ptr::P;
 use rustc_ast::ModKind;
 use rustc_span::symbol::Ident;
 
@@ -374,9 +375,22 @@ impl<'a> State<'a> {
  state.print_visibility(&item.vis)
 });
 }
- ast::ItemKind::Delegation(box delegation) => {
-self.print_delegation(delegation,&item.vis,&item.attrs)
-}
+ ast::ItemKind::Delegation(deleg) => self.print_delegation(
+&item.attrs,
+&item.vis,
+&deleg.qself,
+&deleg.path,
+None,
+&deleg.body,
+),
+ ast::ItemKind::DelegationMac(deleg) => self.print_delegation(
+&item.attrs,
+&item.vis,
+&deleg.qself,
+&deleg.prefix,
+Some(&deleg.suffixes),
+&deleg.body,
+),
 }
 self.ann.post(self,AnnNode::Item(item))
 }
@@ -553,31 +567,63 @@ impl<'a> State<'a> {
 self.word(";");
 }
 }
- ast::AssocItemKind::Delegation(box delegation) => {
-self.print_delegation(delegation, vis,&item.attrs)
-}
+ ast::AssocItemKind::Delegation(deleg) => self.print_delegation(
+&item.attrs,
+ vis,
+&deleg.qself,
+&deleg.path,
+None,
+&deleg.body,
+),
+ ast::AssocItemKind::DelegationMac(deleg) => self.print_delegation(
+&item.attrs,
+ vis,
+&deleg.qself,
+&deleg.prefix,
+Some(&deleg.suffixes),
+&deleg.body,
+),
 }
 self.ann.post(self,AnnNode::SubItem(id))
 }
 
 pub(crate)fnprint_delegation(
 &mutself,
-delegation:&ast::Delegation,
-vis:&ast::Visibility,
 attrs:&[ast::Attribute],
+vis:&ast::Visibility,
+qself:&Option<P<ast::QSelf>>,
+path:&ast::Path,
+suffixes:Option<&[(Ident,Option<Ident>)]>,
+body:&Option<P<ast::Block>>,
 ){
-ifdelegation.body.is_some(){
+if body.is_some(){
 self.head("");
 }
 self.print_visibility(vis);
-self.word_space("reuse");
+self.word_nbsp("reuse");
 
-ifletSome(qself) = &delegation.qself{
-self.print_qpath(&delegation.path, qself,false);
+ifletSome(qself) = qself {
+self.print_qpath(path, qself,false);
 }else{
-self.print_path(&delegation.path,false,0);
+self.print_path(path,false,0);
+}
+ifletSome(suffixes) = suffixes {
+self.word("::");
+self.word("{");
+for(i,(ident, rename))in suffixes.iter().enumerate(){
+self.print_ident(*ident);
+ifletSome(rename) = rename {
+self.nbsp();
+self.word_nbsp("as");
+self.print_ident(*rename);
+}
+if i != suffixes.len() - 1{
+self.word_space(",");
+}
+}
+self.word("}");
 }
-ifletSome(body) = &delegation.body{
+ifletSome(body) = body {
 self.nbsp();
 self.print_block_with_attrs(body, attrs);
 }else{

compiler/rustc_expand/messages.ftl

@@ -30,6 +30,9 @@ expand_duplicate_matcher_binding = duplicate matcher binding
 .label = duplicate binding
 .label2 = previous binding
 
+expand_empty_delegation_list =
+ empty list delegation is not supported
+
 expand_expected_paren_or_brace =
  expected `(` or `{"{"}`, found `{$token}`
 

compiler/rustc_expand/src/errors.rs

@@ -433,3 +433,10 @@ pub struct ExpectedParenOrBrace<'a> {
 pubspan:Span,
 pubtoken:Cow<'a,str>,
 }
+
+#[derive(Diagnostic)]
+#[diag(expand_empty_delegation_list)]
+pub(crate)structEmptyDelegationList{
+#[primary_span]
+pubspan:Span,
+}