rustdoc: box ItemKind::Trait

This reduces the memory consumption of ItemKind.

Author: notriddle

src/librustdoc/clean/inline.rs

@@ -62,7 +62,7 @@ pub(crate) fn try_inline(
         Res::Def(DefKind::Trait, did) => {
             record_extern_fqn(cx, did, ItemType::Trait);
             build_impls(cx, Some(parent_module), did, attrs, &mut ret);
-            clean::TraitItem(build_external_trait(cx, did))
+            clean::TraitItem(Box::new(build_external_trait(cx, did)))
         }
         Res::Def(DefKind::Fn, did) => {
             record_extern_fqn(cx, did, ItemType::Function);

src/librustdoc/clean/mod.rs

@@ -1951,12 +1951,12 @@ fn clean_maybe_renamed_item<'tcx>(
                     .map(|ti| clean_trait_item(cx.tcx.hir().trait_item(ti.id), cx))
                     .collect();
 
-                TraitItem(Trait {
+                TraitItem(Box::new(Trait {
                     def_id,
                     items,
                     generics: clean_generics(generics, cx),
                     bounds: bounds.iter().filter_map(|x| clean_generic_bound(x, cx)).collect(),
-                })
+                }))
             }
             ItemKind::ExternCrate(orig_name) => {
                 return clean_extern_crate(item, name, orig_name, cx);

src/librustdoc/clean/types.rs

@@ -727,7 +727,7 @@ pub(crate) enum ItemKind {
     OpaqueTyItem(OpaqueTy),
     StaticItem(Static),
     ConstantItem(Constant),
-    TraitItem(Trait),
+    TraitItem(Box<Trait>),
     TraitAliasItem(TraitAlias),
     ImplItem(Box<Impl>),
     /// A required method in a trait declaration meaning it's only a function signature.
@@ -2497,7 +2497,7 @@ mod size_asserts {
     static_assert_size!(GenericArgs, 32);
     static_assert_size!(GenericParamDef, 56);
     static_assert_size!(Item, 56);
-    static_assert_size!(ItemKind, 112);
+    static_assert_size!(ItemKind, 96);
     static_assert_size!(PathSegment, 40);
     static_assert_size!(Type, 56);
 }

src/librustdoc/formats/cache.rs

@@ -227,7 +227,7 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
         if let clean::TraitItem(ref t) = *item.kind {
             self.cache.traits.entry(item.item_id.expect_def_id()).or_insert_with(|| {
                 clean::TraitWithExtraInfo {
-                    trait_: t.clone(),
+                    trait_: *t.clone(),
                     is_notable: item.attrs.has_doc_flag(sym::notable_trait),
                 }
             });

src/librustdoc/json/conversions.rs

@@ -248,7 +248,7 @@ fn from_clean_item(item: clean::Item, tcx: TyCtxt<'_>) -> ItemEnum {
         VariantItem(v) => ItemEnum::Variant(v.into_tcx(tcx)),
         FunctionItem(f) => ItemEnum::Function(from_function(f, header.unwrap(), tcx)),
         ForeignFunctionItem(f) => ItemEnum::Function(from_function(f, header.unwrap(), tcx)),
-        TraitItem(t) => ItemEnum::Trait(t.into_tcx(tcx)),
+        TraitItem(t) => ItemEnum::Trait((*t).into_tcx(tcx)),
         TraitAliasItem(t) => ItemEnum::TraitAlias(t.into_tcx(tcx)),
         MethodItem(m, _) => ItemEnum::Method(from_function_method(m, true, header.unwrap(), tcx)),
         TyMethodItem(m) => ItemEnum::Method(from_function_method(m, false, header.unwrap(), tcx)),