Auto merge of #99577 - est31:remove_box_librustdoc, r=jsha

Remove remaining uses of box syntax from librustdoc

Remove the remaining uses of box syntax from librustdoc. Followup of #99066 where these changes were split out because they were responsible for a small but noticeable regression. This PR avoids the regression by boxing some large variants of `ItemKind` to reduce the enum's size by half from 224 bytes to 112 bytes (on x86-64). This should also help with reducing memory usage.

Author: bors

src/librustdoc/clean/auto_trait.rs

@@ -117,15 +117,15 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
             attrs: Default::default(),
             visibility: Inherited,
             item_id: ItemId::Auto { trait_: trait_def_id, for_: item_def_id },
-            kind: Box::new(ImplItem(Impl {
+            kind: Box::new(ImplItem(Box::new(Impl {
                 unsafety: hir::Unsafety::Normal,
                 generics: new_generics,
                 trait_: Some(trait_ref.clean(self.cx)),
                 for_: clean_middle_ty(ty, self.cx, None),
                 items: Vec::new(),
                 polarity,
                 kind: ImplKind::Auto,
-            })),
+            }))),
             cfg: None,
         })
     }

src/librustdoc/clean/blanket_impl.rs

@@ -106,7 +106,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                         attrs: Default::default(),
                         visibility: Inherited,
                         item_id: ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
-                        kind: Box::new(ImplItem(Impl {
+                        kind: Box::new(ImplItem(Box::new(Impl {
                             unsafety: hir::Unsafety::Normal,
                             generics: clean_ty_generics(
                                 cx,
@@ -124,7 +124,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                                 .collect::<Vec<_>>(),
                             polarity: ty::ImplPolarity::Positive,
                             kind: ImplKind::Blanket(Box::new(clean_middle_ty(trait_ref.0.self_ty(), cx, None))),
-                        })),
+                        }))),
                         cfg: None,
                     });
                 }

src/librustdoc/clean/inline.rs

@@ -218,7 +218,7 @@ pub(crate) fn build_external_trait(cx: &mut DocContext<'_>, did: DefId) -> clean
     clean::Trait { def_id: did, generics, items: trait_items, bounds: supertrait_bounds }
 }
 
-fn build_external_function<'tcx>(cx: &mut DocContext<'tcx>, did: DefId) -> clean::Function {
+fn build_external_function<'tcx>(cx: &mut DocContext<'tcx>, did: DefId) -> Box<clean::Function> {
     let sig = cx.tcx.fn_sig(did);
 
     let predicates = cx.tcx.predicates_of(did);
@@ -228,7 +228,7 @@ fn build_external_function<'tcx>(cx: &mut DocContext<'tcx>, did: DefId) -> clean
         let decl = clean_fn_decl_from_did_and_sig(cx, Some(did), sig);
         (generics, decl)
     });
-    clean::Function { decl, generics }
+    Box::new(clean::Function { decl, generics })
 }
 
 fn build_enum(cx: &mut DocContext<'_>, did: DefId) -> clean::Enum {
@@ -260,15 +260,15 @@ fn build_union(cx: &mut DocContext<'_>, did: DefId) -> clean::Union {
     clean::Union { generics, fields }
 }
 
-fn build_type_alias(cx: &mut DocContext<'_>, did: DefId) -> clean::Typedef {
+fn build_type_alias(cx: &mut DocContext<'_>, did: DefId) -> Box<clean::Typedef> {
     let predicates = cx.tcx.explicit_predicates_of(did);
     let type_ = clean_middle_ty(cx.tcx.type_of(did), cx, Some(did));
 
-    clean::Typedef {
+    Box::new(clean::Typedef {
         type_,
         generics: clean_ty_generics(cx, cx.tcx.generics_of(did), predicates),
         item_type: None,
-    }
+    })
 }
 
 /// Builds all inherent implementations of an ADT (struct/union/enum) or Trait item/path/reexport.
@@ -493,7 +493,7 @@ pub(crate) fn build_impl(
     ret.push(clean::Item::from_def_id_and_attrs_and_parts(
         did,
         None,
-        clean::ImplItem(clean::Impl {
+        clean::ImplItem(Box::new(clean::Impl {
             unsafety: hir::Unsafety::Normal,
             generics,
             trait_,
@@ -505,7 +505,7 @@ pub(crate) fn build_impl(
             } else {
                 ImplKind::Normal
             },
-        }),
+        })),
         Box::new(merged_attrs),
         cx,
         cfg,
@@ -538,7 +538,7 @@ fn build_module(
                     attrs: Box::new(clean::Attributes::default()),
                     item_id: ItemId::Primitive(prim_ty, did.krate),
                     visibility: clean::Public,
-                    kind: box clean::ImportItem(clean::Import::new_simple(
+                    kind: Box::new(clean::ImportItem(clean::Import::new_simple(
                         item.ident.name,
                         clean::ImportSource {
                             path: clean::Path {
@@ -554,7 +554,7 @@ fn build_module(
                             did: None,
                         },
                         true,
-                    )),
+                    ))),
                     cfg: None,
                 });
             } else if let Some(i) = try_inline(cx, did, None, res, item.ident.name, None, visited) {

src/librustdoc/clean/mod.rs

@@ -908,15 +908,15 @@ fn clean_function<'tcx>(
     sig: &hir::FnSig<'tcx>,
     generics: &hir::Generics<'tcx>,
     body_id: hir::BodyId,
-) -> Function {
+) -> Box<Function> {
     let (generics, decl) = enter_impl_trait(cx, |cx| {
         // NOTE: generics must be cleaned before args
         let generics = generics.clean(cx);
         let args = clean_args_from_types_and_body_id(cx, sig.decl.inputs, body_id);
         let decl = clean_fn_decl_with_args(cx, sig.decl, args);
         (generics, decl)
     });
-    Function { decl, generics }
+    Box::new(Function { decl, generics })
 }
 
 fn clean_args_from_types_and_names<'tcx>(
@@ -1061,18 +1061,18 @@ impl<'tcx> Clean<'tcx, Item> for hir::TraitItem<'tcx> {
                         let decl = clean_fn_decl_with_args(cx, sig.decl, args);
                         (generics, decl)
                     });
-                    TyMethodItem(Function { decl, generics })
+                    TyMethodItem(Box::new(Function { decl, generics }))
                 }
                 hir::TraitItemKind::Type(bounds, Some(default)) => {
                     let generics = enter_impl_trait(cx, |cx| self.generics.clean(cx));
                     let bounds = bounds.iter().filter_map(|x| x.clean(cx)).collect();
                     let item_type = clean_middle_ty(hir_ty_to_ty(cx.tcx, default), cx, None);
                     AssocTypeItem(
-                        Typedef {
+                        Box::new(Typedef {
                             type_: clean_ty(default, cx),
                             generics,
                             item_type: Some(item_type),
-                        },
+                        }),
                         bounds,
                     )
                 }
@@ -1109,7 +1109,7 @@ impl<'tcx> Clean<'tcx, Item> for hir::ImplItem<'tcx> {
                     let generics = self.generics.clean(cx);
                     let item_type = clean_middle_ty(hir_ty_to_ty(cx.tcx, hir_ty), cx, None);
                     AssocTypeItem(
-                        Typedef { type_, generics, item_type: Some(item_type) },
+                        Box::new(Typedef { type_, generics, item_type: Some(item_type) }),
                         Vec::new(),
                     )
                 }
@@ -1186,9 +1186,9 @@ impl<'tcx> Clean<'tcx, Item> for ty::AssocItem {
                         ty::ImplContainer(_) => Some(self.defaultness),
                         ty::TraitContainer(_) => None,
                     };
-                    MethodItem(Function { generics, decl }, defaultness)
+                    MethodItem(Box::new(Function { generics, decl }), defaultness)
                 } else {
-                    TyMethodItem(Function { generics, decl })
+                    TyMethodItem(Box::new(Function { generics, decl }))
                 }
             }
             ty::AssocKind::Type => {
@@ -1282,7 +1282,7 @@ impl<'tcx> Clean<'tcx, Item> for ty::AssocItem {
 
                     if self.defaultness.has_value() {
                         AssocTypeItem(
-                            Typedef {
+                            Box::new(Typedef {
                                 type_: clean_middle_ty(
                                     tcx.type_of(self.def_id),
                                     cx,
@@ -1291,7 +1291,7 @@ impl<'tcx> Clean<'tcx, Item> for ty::AssocItem {
                                 generics,
                                 // FIXME: should we obtain the Type from HIR and pass it on here?
                                 item_type: None,
-                            },
+                            }),
                             bounds,
                         )
                     } else {
@@ -1300,11 +1300,11 @@ impl<'tcx> Clean<'tcx, Item> for ty::AssocItem {
                 } else {
                     // FIXME: when could this happen? Associated items in inherent impls?
                     AssocTypeItem(
-                        Typedef {
+                        Box::new(Typedef {
                             type_: clean_middle_ty(tcx.type_of(self.def_id), cx, Some(self.def_id)),
                             generics: Generics { params: Vec::new(), where_predicates: Vec::new() },
                             item_type: None,
-                        },
+                        }),
                         Vec::new(),
                     )
                 }
@@ -1949,11 +1949,11 @@ fn clean_maybe_renamed_item<'tcx>(
             ItemKind::TyAlias(hir_ty, generics) => {
                 let rustdoc_ty = clean_ty(hir_ty, cx);
                 let ty = clean_middle_ty(hir_ty_to_ty(cx.tcx, hir_ty), cx, None);
-                TypedefItem(Typedef {
+                TypedefItem(Box::new(Typedef {
                     type_: rustdoc_ty,
                     generics: generics.clean(cx),
                     item_type: Some(ty),
-                })
+                }))
             }
             ItemKind::Enum(ref def, generics) => EnumItem(Enum {
                 variants: def.variants.iter().map(|v| v.clean(cx)).collect(),
@@ -2041,7 +2041,7 @@ fn clean_impl<'tcx>(
         _ => None,
     });
     let mut make_item = |trait_: Option<Path>, for_: Type, items: Vec<Item>| {
-        let kind = ImplItem(Impl {
+        let kind = ImplItem(Box::new(Impl {
             unsafety: impl_.unsafety,
             generics: impl_.generics.clean(cx),
             trait_,
@@ -2053,7 +2053,7 @@ fn clean_impl<'tcx>(
             } else {
                 ImplKind::Normal
             },
-        });
+        }));
         Item::from_hir_id_and_parts(hir_id, None, kind, cx)
     };
     if let Some(type_alias) = type_alias {
@@ -2108,7 +2108,7 @@ fn clean_extern_crate<'tcx>(
         attrs: Box::new(attrs.clean(cx)),
         item_id: crate_def_id.into(),
         visibility: clean_visibility(ty_vis),
-        kind: box ExternCrateItem { src: orig_name },
+        kind: Box::new(ExternCrateItem { src: orig_name }),
         cfg: attrs.cfg(cx.tcx, &cx.cache.hidden_cfg),
     }]
 }
@@ -2243,7 +2243,7 @@ fn clean_maybe_renamed_foreign_item<'tcx>(
                     let decl = clean_fn_decl_with_args(cx, decl, args);
                     (generics, decl)
                 });
-                ForeignFunctionItem(Function { decl, generics })
+                ForeignFunctionItem(Box::new(Function { decl, generics }))
             }
             hir::ForeignItemKind::Static(ty, mutability) => {
                 ForeignStaticItem(Static { type_: clean_ty(ty, cx), mutability, expr: None })

src/librustdoc/clean/types.rs

@@ -430,8 +430,8 @@ impl Item {
         };
         match kind {
             ItemKind::ModuleItem(Module { span, .. }) => *span,
-            ItemKind::ImplItem(Impl { kind: ImplKind::Auto, .. }) => Span::dummy(),
-            ItemKind::ImplItem(Impl { kind: ImplKind::Blanket(_), .. }) => {
+            ItemKind::ImplItem(box Impl { kind: ImplKind::Auto, .. }) => Span::dummy(),
+            ItemKind::ImplItem(box Impl { kind: ImplKind::Blanket(_), .. }) => {
                 if let ItemId::Blanket { impl_id, .. } = self.item_id {
                     rustc_span(impl_id, tcx)
                 } else {
@@ -502,7 +502,7 @@ impl Item {
             clean_visibility(cx.tcx.visibility(def_id))
         };
 
-        Item { item_id: def_id.into(), kind: box kind, name, attrs, visibility, cfg }
+        Item { item_id: def_id.into(), kind: Box::new(kind), name, attrs, visibility, cfg }
     }
 
     /// Finds all `doc` attributes as NameValues and returns their corresponding values, joined
@@ -730,25 +730,25 @@ pub(crate) enum ItemKind {
     StructItem(Struct),
     UnionItem(Union),
     EnumItem(Enum),
-    FunctionItem(Function),
+    FunctionItem(Box<Function>),
     ModuleItem(Module),
-    TypedefItem(Typedef),
+    TypedefItem(Box<Typedef>),
     OpaqueTyItem(OpaqueTy),
     StaticItem(Static),
     ConstantItem(Constant),
     TraitItem(Trait),
     TraitAliasItem(TraitAlias),
-    ImplItem(Impl),
+    ImplItem(Box<Impl>),
     /// A required method in a trait declaration meaning it's only a function signature.
-    TyMethodItem(Function),
+    TyMethodItem(Box<Function>),
     /// A method in a trait impl or a provided method in a trait declaration.
     ///
     /// Compared to [TyMethodItem], it also contains a method body.
-    MethodItem(Function, Option<hir::Defaultness>),
+    MethodItem(Box<Function>, Option<hir::Defaultness>),
     StructFieldItem(Type),
     VariantItem(Variant),
     /// `fn`s from an extern block
-    ForeignFunctionItem(Function),
+    ForeignFunctionItem(Box<Function>),
     /// `static`s from an extern block
     ForeignStaticItem(Static),
     /// `type`s from an extern block
@@ -765,12 +765,16 @@ pub(crate) enum ItemKind {
     /// The bounds may be non-empty if there is a `where` clause.
     TyAssocTypeItem(Box<Generics>, Vec<GenericBound>),
     /// An associated type in a trait impl or a provided one in a trait declaration.
-    AssocTypeItem(Typedef, Vec<GenericBound>),
+    AssocTypeItem(Box<Typedef>, Vec<GenericBound>),
     /// An item that has been stripped by a rustdoc pass
     StrippedItem(Box<ItemKind>),
     KeywordItem,
 }
 
+// `ItemKind` is an enum and large variants can bloat up memory usage even for smaller ones
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+rustc_data_structures::static_assert_size!(ItemKind, 112);
+
 impl ItemKind {
     /// Some items contain others such as structs (for their fields) and Enums
     /// (for their variants). This method returns those contained items.

src/librustdoc/doctest.rs

@@ -740,7 +740,7 @@ fn check_if_attr_is_complete(source: &str, edition: Edition) -> bool {
                 rustc_errors::fallback_fluent_bundle(rustc_errors::DEFAULT_LOCALE_RESOURCES, false);
 
             let emitter = EmitterWriter::new(
-                box io::sink(),
+                Box::new(io::sink()),
                 None,
                 None,
                 fallback_bundle,
@@ -751,7 +751,7 @@ fn check_if_attr_is_complete(source: &str, edition: Edition) -> bool {
                 false,
             );
 
-            let handler = Handler::with_emitter(false, None, box emitter);
+            let handler = Handler::with_emitter(false, None, Box::new(emitter));
             let sess = ParseSess::with_span_handler(handler, sm);
             let mut parser =
                 match maybe_new_parser_from_source_str(&sess, filename, source.to_owned()) {

src/librustdoc/fold.rs

@@ -2,7 +2,7 @@ use crate::clean::*;
 
 pub(crate) fn strip_item(mut item: Item) -> Item {
     if !matches!(*item.kind, StrippedItem(..)) {
-        item.kind = box StrippedItem(item.kind);
+        item.kind = Box::new(StrippedItem(item.kind));
     }
     item
 }
@@ -75,10 +75,10 @@ pub(crate) trait DocFolder: Sized {
 
     /// don't override!
     fn fold_item_recur(&mut self, mut item: Item) -> Item {
-        item.kind = box match *item.kind {
-            StrippedItem(box i) => StrippedItem(box self.fold_inner_recur(i)),
+        item.kind = Box::new(match *item.kind {
+            StrippedItem(box i) => StrippedItem(Box::new(self.fold_inner_recur(i))),
             _ => self.fold_inner_recur(*item.kind),
-        };
+        });
         item
     }
 

src/librustdoc/formats/cache.rs

@@ -536,7 +536,7 @@ enum ParentStackItem {
 impl ParentStackItem {
     fn new(item: &clean::Item) -> Self {
         match &*item.kind {
-            clean::ItemKind::ImplItem(clean::Impl { for_, trait_, generics, kind, .. }) => {
+            clean::ItemKind::ImplItem(box clean::Impl { for_, trait_, generics, kind, .. }) => {
                 ParentStackItem::Impl {
                     for_: for_.clone(),
                     trait_: trait_.clone(),

src/librustdoc/html/render/mod.rs

@@ -1160,7 +1160,7 @@ fn render_deref_methods(
         .items
         .iter()
         .find_map(|item| match *item.kind {
-            clean::AssocTypeItem(ref t, _) => Some(match *t {
+            clean::AssocTypeItem(box ref t, _) => Some(match *t {
                 clean::Typedef { item_type: Some(ref type_), .. } => (type_, &t.type_),
                 _ => (&t.type_, &t.type_),
             }),
@@ -2054,7 +2054,7 @@ fn sidebar_deref_methods(
     debug!("found Deref: {:?}", impl_);
     if let Some((target, real_target)) =
         impl_.inner_impl().items.iter().find_map(|item| match *item.kind {
-            clean::AssocTypeItem(ref t, _) => Some(match *t {
+            clean::AssocTypeItem(box ref t, _) => Some(match *t {
                 clean::Typedef { item_type: Some(ref type_), .. } => (type_, &t.type_),
                 _ => (&t.type_, &t.type_),
             }),