Box ast::ItemKind

This reduces the size of ast::Item from 296 to 96 bytes.

Author: jyn514

compiler/rustc_ast/src/ast.rs

@@ -2581,7 +2581,7 @@ pub struct Item<K = ItemKind> {
     /// It might be a dummy name in case of anonymous items.
     pub ident: Ident,
 
-    pub kind: K,
+    pub kind: Box<K>,
 
     /// Original tokens this item was parsed from. This isn't necessarily
     /// available for all items, although over time more and more items should
@@ -2593,6 +2593,10 @@ pub struct Item<K = ItemKind> {
     pub tokens: Option<LazyTokenStream>,
 }
 
+rustc_data_structures::static_assert_size!(Item<ItemKind>, 96);
+rustc_data_structures::static_assert_size!(Item<AssocItemKind>, 96);
+rustc_data_structures::static_assert_size!(Item<ForeignItemKind>, 96);
+
 impl Item {
     /// Return the span that encompasses the attributes.
     pub fn span_with_attributes(&self) -> Span {
@@ -2603,7 +2607,7 @@ impl Item {
 impl<K: Into<ItemKind>> Item<K> {
     pub fn into_item(self) -> Item {
         let Item { attrs, id, span, vis, ident, kind, tokens } = self;
-        Item { attrs, id, span, vis, ident, kind: kind.into(), tokens }
+        Item { attrs, id, span, vis, ident, kind: box (*kind).into(), tokens }
     }
 }
 

compiler/rustc_ast/src/mut_visit.rs

@@ -971,7 +971,7 @@ pub fn noop_flat_map_assoc_item<T: MutVisitor>(
     visitor.visit_ident(ident);
     visitor.visit_vis(vis);
     visit_attrs(attrs, visitor);
-    match kind {
+    match &mut **kind {
         AssocItemKind::Const(_, ty, expr) => {
             visitor.visit_ty(ty);
             visit_opt(expr, |expr| visitor.visit_expr(expr));
@@ -1014,7 +1014,7 @@ pub fn noop_visit_crate<T: MutVisitor>(krate: &mut Crate, vis: &mut T) {
             id: DUMMY_NODE_ID,
             vis: item_vis,
             span,
-            kind: ItemKind::Mod(module),
+            kind: box ItemKind::Mod(module),
             tokens: None,
         });
         let items = vis.flat_map_item(item);
@@ -1025,7 +1025,7 @@ pub fn noop_visit_crate<T: MutVisitor>(krate: &mut Crate, vis: &mut T) {
             Crate { module, attrs: vec![], span, proc_macros }
         } else if len == 1 {
             let Item { attrs, span, kind, .. } = items.into_iter().next().unwrap().into_inner();
-            match kind {
+            match *kind {
                 ItemKind::Mod(module) => Crate { module, attrs, span, proc_macros },
                 _ => panic!("visitor converted a module to not a module"),
             }
@@ -1061,7 +1061,7 @@ pub fn noop_flat_map_foreign_item<T: MutVisitor>(
     visitor.visit_ident(ident);
     visitor.visit_vis(vis);
     visit_attrs(attrs, visitor);
-    match kind {
+    match &mut **kind {
         ForeignItemKind::Static(ty, _, expr) => {
             visitor.visit_ty(ty);
             visit_opt(expr, |expr| visitor.visit_expr(expr));