delegation: Implement list delegation

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

2 files changed, 9 insertions, 4 deletions

diff --git a/compiler/rustc_passes/src/hir_stats.rs b/compiler/rustc_passes/src/hir_stats.rs
index d7664d1c1ff..a980d5dcaba 100644
--- a/compiler/rustc_passes/src/hir_stats.rs
+++ b/compiler/rustc_passes/src/hir_stats.rs
@@ -522,7 +522,8 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
                 Impl,
                 MacCall,
                 MacroDef,
-                Delegation
+                Delegation,
+                DelegationMac
             ]
         );
         ast_visit::walk_item(self, i)
@@ -650,7 +651,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
     fn visit_assoc_item(&mut self, i: &'v ast::AssocItem, ctxt: ast_visit::AssocCtxt) {
         record_variants!(
             (self, i, i.kind, Id::None, ast, AssocItem, AssocItemKind),
-            [Const, Fn, Type, MacCall, Delegation]
+            [Const, Fn, Type, MacCall, Delegation, DelegationMac]
         );
         ast_visit::walk_assoc_item(self, i, ctxt);
     }
diff --git a/compiler/rustc_passes/src/lang_items.rs b/compiler/rustc_passes/src/lang_items.rs
index c1da8928f30..a5fa94faead 100644
--- a/compiler/rustc_passes/src/lang_items.rs
+++ b/compiler/rustc_passes/src/lang_items.rs
@@ -285,7 +285,9 @@ impl<'ast, 'tcx> visit::Visitor<'ast> for LanguageItemCollector<'ast, 'tcx> {
             ast::ItemKind::TraitAlias(_, _) => Target::TraitAlias,
             ast::ItemKind::Impl(_) => Target::Impl,
             ast::ItemKind::MacroDef(_) => Target::MacroDef,
-            ast::ItemKind::MacCall(_) => unreachable!("macros should have been expanded"),
+            ast::ItemKind::MacCall(_) | ast::ItemKind::DelegationMac(_) => {
+                unreachable!("macros should have been expanded")
+            }
         };
 
         self.check_for_lang(
@@ -340,7 +342,9 @@ impl<'ast, 'tcx> visit::Visitor<'ast> for LanguageItemCollector<'ast, 'tcx> {
             }
             ast::AssocItemKind::Const(ct) => (Target::AssocConst, Some(&ct.generics)),
             ast::AssocItemKind::Type(ty) => (Target::AssocTy, Some(&ty.generics)),
-            ast::AssocItemKind::MacCall(_) => unreachable!("macros should have been expanded"),
+            ast::AssocItemKind::MacCall(_) | ast::AssocItemKind::DelegationMac(_) => {
+                unreachable!("macros should have been expanded")
+            }
         };
 
         self.check_for_lang(