From 39fbcdf926b214f407332bde8b91e9b0d66d211b Mon Sep 17 00:00:00 2001
From: Michael Howell <michael@notriddle.com>
Date: Fri, 26 Jul 2024 23:47:09 -0700
Subject: [PATCH] rustdoc: use strategic ThinVec/Box to shrink
 `clean::ItemKind`

---
 src/librustdoc/clean/inline.rs                | 12 ++--
 src/librustdoc/clean/mod.rs                   | 57 ++++++++++---------
 src/librustdoc/clean/types.rs                 | 24 ++++----
 src/librustdoc/fold.rs                        |  2 +-
 src/librustdoc/html/format.rs                 |  2 +-
 src/librustdoc/html/render/mod.rs             | 51 ++++++++++++-----
 src/librustdoc/html/render/print_item.rs      |  6 +-
 src/librustdoc/json/conversions.rs            | 21 +++++--
 .../passes/check_doc_test_visibility.rs       |  2 +-
 src/librustdoc/visit.rs                       |  2 +-
 10 files changed, 111 insertions(+), 68 deletions(-)

diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 0024e246ef007..2b272d2019ac2 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -131,8 +131,8 @@ pub(crate) fn try_inline(
         Res::Def(DefKind::Const, did) => {
             record_extern_fqn(cx, did, ItemType::Constant);
             cx.with_param_env(did, |cx| {
-                let (generics, ty, ct) = build_const_item(cx, did);
-                clean::ConstantItem(generics, Box::new(ty), ct)
+                let ct = build_const_item(cx, did);
+                clean::ConstantItem(Box::new(ct))
             })
         }
         Res::Def(DefKind::Macro(kind), did) => {
@@ -723,7 +723,7 @@ pub(crate) fn print_inlined_const(tcx: TyCtxt<'_>, did: DefId) -> String {
 fn build_const_item(
     cx: &mut DocContext<'_>,
     def_id: DefId,
-) -> (clean::Generics, clean::Type, clean::Constant) {
+) -> clean::Constant {
     let mut generics =
         clean_ty_generics(cx, cx.tcx.generics_of(def_id), cx.tcx.explicit_predicates_of(def_id));
     clean::simplify::move_bounds_to_generic_parameters(&mut generics);
@@ -733,17 +733,17 @@ fn build_const_item(
         None,
         None,
     );
-    (generics, ty, clean::Constant { kind: clean::ConstantKind::Extern { def_id } })
+    clean::Constant { generics, type_: ty, kind: clean::ConstantKind::Extern { def_id } }
 }
 
 fn build_static(cx: &mut DocContext<'_>, did: DefId, mutable: bool) -> clean::Static {
     clean::Static {
-        type_: clean_middle_ty(
+        type_: Box::new(clean_middle_ty(
             ty::Binder::dummy(cx.tcx.type_of(did).instantiate_identity()),
             cx,
             Some(did),
             None,
-        ),
+        )),
         mutability: if mutable { Mutability::Mut } else { Mutability::Not },
         expr: None,
     }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 26011926cddda..3d8e92014c9ad 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -287,13 +287,13 @@ fn clean_lifetime<'tcx>(lifetime: &hir::Lifetime, cx: &mut DocContext<'tcx>) ->
 pub(crate) fn clean_const<'tcx>(
     constant: &hir::ConstArg<'tcx>,
     _cx: &mut DocContext<'tcx>,
-) -> Constant {
+) -> ConstantKind {
     match &constant.kind {
         hir::ConstArgKind::Path(qpath) => {
-            Constant { kind: ConstantKind::Path { path: qpath_to_string(&qpath).into() } }
+            ConstantKind::Path { path: qpath_to_string(&qpath).into() }
         }
         hir::ConstArgKind::Anon(anon) => {
-            Constant { kind: ConstantKind::Anonymous { body: anon.body } }
+            ConstantKind::Anonymous { body: anon.body }
         }
     }
 }
@@ -301,9 +301,9 @@ pub(crate) fn clean_const<'tcx>(
 pub(crate) fn clean_middle_const<'tcx>(
     constant: ty::Binder<'tcx, ty::Const<'tcx>>,
     _cx: &mut DocContext<'tcx>,
-) -> Constant {
+) -> ConstantKind {
     // FIXME: instead of storing the stringified expression, store `self` directly instead.
-    Constant { kind: ConstantKind::TyConst { expr: constant.skip_binder().to_string().into() } }
+    ConstantKind::TyConst { expr: constant.skip_binder().to_string().into() }
 }
 
 pub(crate) fn clean_middle_region<'tcx>(region: ty::Region<'tcx>) -> Option<Lifetime> {
@@ -1231,12 +1231,11 @@ fn clean_trait_item<'tcx>(trait_item: &hir::TraitItem<'tcx>, cx: &mut DocContext
     cx.with_param_env(local_did, |cx| {
         let inner = match trait_item.kind {
             hir::TraitItemKind::Const(ty, Some(default)) => {
-                let generics = enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx));
-                AssocConstItem(
-                    generics,
-                    Box::new(clean_ty(ty, cx)),
-                    ConstantKind::Local { def_id: local_did, body: default },
-                )
+                AssocConstItem(Box::new(Constant {
+                    generics: enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx)),
+                    kind: ConstantKind::Local { def_id: local_did, body: default },
+                    type_: clean_ty(ty, cx),
+                }))
             }
             hir::TraitItemKind::Const(ty, None) => {
                 let generics = enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx));
@@ -1283,9 +1282,11 @@ pub(crate) fn clean_impl_item<'tcx>(
     cx.with_param_env(local_did, |cx| {
         let inner = match impl_.kind {
             hir::ImplItemKind::Const(ty, expr) => {
-                let generics = clean_generics(impl_.generics, cx);
-                let default = ConstantKind::Local { def_id: local_did, body: expr };
-                AssocConstItem(generics, Box::new(clean_ty(ty, cx)), default)
+                AssocConstItem(Box::new(Constant {
+                    generics: clean_generics(impl_.generics, cx),
+                    kind: ConstantKind::Local { def_id: local_did, body: expr },
+                    type_: clean_ty(ty, cx),
+                }))
             }
             hir::ImplItemKind::Fn(ref sig, body) => {
                 let m = clean_function(cx, sig, impl_.generics, FunctionArgs::Body(body));
@@ -1320,12 +1321,12 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
     let tcx = cx.tcx;
     let kind = match assoc_item.kind {
         ty::AssocKind::Const => {
-            let ty = Box::new(clean_middle_ty(
+            let ty = clean_middle_ty(
                 ty::Binder::dummy(tcx.type_of(assoc_item.def_id).instantiate_identity()),
                 cx,
                 Some(assoc_item.def_id),
                 None,
-            ));
+            );
 
             let mut generics = clean_ty_generics(
                 cx,
@@ -1339,9 +1340,13 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
                 ty::TraitContainer => tcx.defaultness(assoc_item.def_id).has_value(),
             };
             if provided {
-                AssocConstItem(generics, ty, ConstantKind::Extern { def_id: assoc_item.def_id })
+                AssocConstItem(Box::new(Constant {
+                    generics,
+                    kind: ConstantKind::Extern { def_id: assoc_item.def_id },
+                    type_: ty,
+                }))
             } else {
-                TyAssocConstItem(generics, ty)
+                TyAssocConstItem(generics, Box::new(ty))
             }
         }
         ty::AssocKind::Fn => {
@@ -1397,7 +1402,7 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
                     {
                         true
                     }
-                    (GenericParamDefKind::Const { .. }, GenericArg::Const(c)) => match &c.kind {
+                    (GenericParamDefKind::Const { .. }, GenericArg::Const(c)) => match &**c {
                         ConstantKind::TyConst { expr } => **expr == *param.name.as_str(),
                         _ => false,
                     },
@@ -2745,13 +2750,13 @@ fn clean_maybe_renamed_item<'tcx>(
     cx.with_param_env(def_id, |cx| {
         let kind = match item.kind {
             ItemKind::Static(ty, mutability, body_id) => {
-                StaticItem(Static { type_: clean_ty(ty, cx), mutability, expr: Some(body_id) })
+                StaticItem(Static { type_: Box::new(clean_ty(ty, cx)), mutability, expr: Some(body_id) })
             }
-            ItemKind::Const(ty, generics, body_id) => ConstantItem(
-                clean_generics(generics, cx),
-                Box::new(clean_ty(ty, cx)),
-                Constant { kind: ConstantKind::Local { body: body_id, def_id } },
-            ),
+            ItemKind::Const(ty, generics, body_id) => ConstantItem(Box::new(Constant {
+                generics: clean_generics(generics, cx),
+                type_: clean_ty(ty, cx),
+                kind: ConstantKind::Local { body: body_id, def_id }
+            })),
             ItemKind::OpaqueTy(ref ty) => OpaqueTyItem(OpaqueTy {
                 bounds: ty.bounds.iter().filter_map(|x| clean_generic_bound(x, cx)).collect(),
                 generics: clean_generics(ty.generics, cx),
@@ -3109,7 +3114,7 @@ fn clean_maybe_renamed_foreign_item<'tcx>(
                 ForeignFunctionItem(Box::new(Function { decl, generics }), safety)
             }
             hir::ForeignItemKind::Static(ty, mutability, safety) => ForeignStaticItem(
-                Static { type_: clean_ty(ty, cx), mutability, expr: None },
+                Static { type_: Box::new(clean_ty(ty, cx)), mutability, expr: None },
                 safety,
             ),
             hir::ForeignItemKind::Type => ForeignTypeItem,
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index 3709953159686..92fe98130e859 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -852,9 +852,9 @@ pub(crate) enum ItemKind {
     PrimitiveItem(PrimitiveType),
     /// A required associated constant in a trait declaration.
     TyAssocConstItem(Generics, Box<Type>),
-    ConstantItem(Generics, Box<Type>, Constant),
+    ConstantItem(Box<Constant>),
     /// An associated constant in a trait impl or a provided one in a trait declaration.
-    AssocConstItem(Generics, Box<Type>, ConstantKind),
+    AssocConstItem(Box<Constant>),
     /// A required associated type in a trait declaration.
     ///
     /// The bounds may be non-empty if there is a `where` clause.
@@ -888,7 +888,7 @@ impl ItemKind {
             | TypeAliasItem(_)
             | OpaqueTyItem(_)
             | StaticItem(_)
-            | ConstantItem(_, _, _)
+            | ConstantItem(_)
             | TraitAliasItem(_)
             | TyMethodItem(_)
             | MethodItem(_, _)
@@ -922,7 +922,7 @@ impl ItemKind {
                 | TypeAliasItem(_)
                 | OpaqueTyItem(_)
                 | StaticItem(_)
-                | ConstantItem(_, _, _)
+                | ConstantItem(_)
                 | TraitAliasItem(_)
                 | ForeignFunctionItem(_, _)
                 | ForeignStaticItem(_, _)
@@ -2050,7 +2050,7 @@ impl From<hir::PrimTy> for PrimitiveType {
 pub(crate) struct Struct {
     pub(crate) ctor_kind: Option<CtorKind>,
     pub(crate) generics: Generics,
-    pub(crate) fields: Vec<Item>,
+    pub(crate) fields: ThinVec<Item>,
 }
 
 impl Struct {
@@ -2076,7 +2076,7 @@ impl Union {
 /// only as a variant in an enum.
 #[derive(Clone, Debug)]
 pub(crate) struct VariantStruct {
-    pub(crate) fields: Vec<Item>,
+    pub(crate) fields: ThinVec<Item>,
 }
 
 impl VariantStruct {
@@ -2110,7 +2110,7 @@ pub(crate) struct Variant {
 #[derive(Clone, Debug)]
 pub(crate) enum VariantKind {
     CLike,
-    Tuple(Vec<Item>),
+    Tuple(ThinVec<Item>),
     Struct(VariantStruct),
 }
 
@@ -2246,7 +2246,7 @@ impl Path {
 pub(crate) enum GenericArg {
     Lifetime(Lifetime),
     Type(Type),
-    Const(Box<Constant>),
+    Const(Box<ConstantKind>),
     Infer,
 }
 
@@ -2359,20 +2359,22 @@ pub(crate) struct BareFunctionDecl {
 
 #[derive(Clone, Debug)]
 pub(crate) struct Static {
-    pub(crate) type_: Type,
+    pub(crate) type_: Box<Type>,
     pub(crate) mutability: Mutability,
     pub(crate) expr: Option<BodyId>,
 }
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub(crate) struct Constant {
+    pub(crate) generics: Generics,
     pub(crate) kind: ConstantKind,
+    pub(crate) type_: Type,
 }
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub(crate) enum Term {
     Type(Type),
-    Constant(Constant),
+    Constant(ConstantKind),
 }
 
 impl Term {
@@ -2594,7 +2596,7 @@ mod size_asserts {
     static_assert_size!(GenericParamDef, 40);
     static_assert_size!(Generics, 16);
     static_assert_size!(Item, 56);
-    static_assert_size!(ItemKind, 56);
+    static_assert_size!(ItemKind, 48);
     static_assert_size!(PathSegment, 40);
     static_assert_size!(Type, 32);
     // tidy-alphabetical-end
diff --git a/src/librustdoc/fold.rs b/src/librustdoc/fold.rs
index 346e9a4e113a5..beb7686e29c56 100644
--- a/src/librustdoc/fold.rs
+++ b/src/librustdoc/fold.rs
@@ -79,7 +79,7 @@ pub(crate) trait DocFolder: Sized {
             | FunctionItem(_)
             | OpaqueTyItem(_)
             | StaticItem(_)
-            | ConstantItem(_, _, _)
+            | ConstantItem(..)
             | TraitAliasItem(_)
             | TyMethodItem(_)
             | MethodItem(_, _)
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 055781f7fed72..18ee04a2f4d5f 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -375,7 +375,7 @@ impl clean::Lifetime {
     }
 }
 
-impl clean::Constant {
+impl clean::ConstantKind {
     pub(crate) fn print(&self, tcx: TyCtxt<'_>) -> impl Display + '_ {
         let expr = self.expr(tcx);
         display_fn(
diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 5b9ef67109cf2..4bf264fcd30ac 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -1090,17 +1090,25 @@ fn render_assoc_item(
         clean::MethodItem(m, _) => {
             assoc_method(w, item, &m.generics, &m.decl, link, parent, cx, render_mode)
         }
-        kind @ (clean::TyAssocConstItem(generics, ty) | clean::AssocConstItem(generics, ty, _)) => {
+        clean::TyAssocConstItem(generics, ty) => {
             assoc_const(
                 w,
                 item,
                 generics,
                 ty,
-                match kind {
-                    clean::TyAssocConstItem(..) => None,
-                    clean::AssocConstItem(.., default) => Some(default),
-                    _ => unreachable!(),
-                },
+                None,
+                link,
+                if parent == ItemType::Trait { 4 } else { 0 },
+                cx,
+            )
+        }
+        clean::AssocConstItem(ci) => {
+            assoc_const(
+                w,
+                item,
+                &ci.generics,
+                &ci.type_,
+                Some(&ci.kind),
                 link,
                 if parent == ItemType::Trait { 4 } else { 0 },
                 cx,
@@ -1690,8 +1698,7 @@ fn render_impl(
                     w.write_str("</h4></section>");
                 }
             }
-            kind @ (clean::TyAssocConstItem(generics, ty)
-            | clean::AssocConstItem(generics, ty, _)) => {
+            clean::TyAssocConstItem(generics, ty) => {
                 let source_id = format!("{item_type}.{name}");
                 let id = cx.derive_id(&source_id);
                 write!(w, "<section id=\"{id}\" class=\"{item_type}{in_trait_class}\">");
@@ -1706,11 +1713,29 @@ fn render_impl(
                     item,
                     generics,
                     ty,
-                    match kind {
-                        clean::TyAssocConstItem(..) => None,
-                        clean::AssocConstItem(.., default) => Some(default),
-                        _ => unreachable!(),
-                    },
+                    None,
+                    link.anchor(if trait_.is_some() { &source_id } else { &id }),
+                    0,
+                    cx,
+                );
+                w.write_str("</h4></section>");
+            }
+            clean::AssocConstItem(ci) => {
+                let source_id = format!("{item_type}.{name}");
+                let id = cx.derive_id(&source_id);
+                write!(w, "<section id=\"{id}\" class=\"{item_type}{in_trait_class}\">");
+                render_rightside(w, cx, item, render_mode);
+                if trait_.is_some() {
+                    // Anchors are only used on trait impls.
+                    write!(w, "<a href=\"#{id}\" class=\"anchor\">§</a>");
+                }
+                w.write_str("<h4 class=\"code-header\">");
+                assoc_const(
+                    w,
+                    item,
+                    &ci.generics,
+                    &ci.type_,
+                    Some(&ci.kind),
                     link.anchor(if trait_.is_some() { &source_id } else { &id }),
                     0,
                     cx,
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index cf78a1d223c89..0cf62ccf6e7ff 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -267,7 +267,7 @@ pub(super) fn print_item(cx: &mut Context<'_>, item: &clean::Item, buf: &mut Buf
         clean::PrimitiveItem(_) => item_primitive(buf, cx, item),
         clean::StaticItem(ref i) => item_static(buf, cx, item, i, None),
         clean::ForeignStaticItem(ref i, safety) => item_static(buf, cx, item, i, Some(*safety)),
-        clean::ConstantItem(generics, ty, c) => item_constant(buf, cx, item, generics, ty, c),
+        clean::ConstantItem(ci) => item_constant(buf, cx, item, &ci.generics, &ci.type_, &ci.kind),
         clean::ForeignTypeItem => item_foreign_type(buf, cx, item),
         clean::KeywordItem => item_keyword(buf, cx, item),
         clean::OpaqueTyItem(ref e) => item_opaque_ty(buf, cx, item, e),
@@ -1841,7 +1841,7 @@ fn item_constant(
     it: &clean::Item,
     generics: &clean::Generics,
     ty: &clean::Type,
-    c: &clean::Constant,
+    c: &clean::ConstantKind,
 ) {
     wrap_item(w, |w| {
         let tcx = cx.tcx();
@@ -1911,7 +1911,7 @@ fn item_fields(
     w: &mut Buffer,
     cx: &mut Context<'_>,
     it: &clean::Item,
-    fields: &Vec<clean::Item>,
+    fields: &[clean::Item],
     ctor_kind: Option<CtorKind>,
 ) {
     let mut fields = fields
diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
index 4ab0df3670859..1dcd92e7124cd 100644
--- a/src/librustdoc/json/conversions.rs
+++ b/src/librustdoc/json/conversions.rs
@@ -188,6 +188,16 @@ impl FromWithTcx<clean::Constant> for Constant {
     }
 }
 
+impl FromWithTcx<clean::ConstantKind> for Constant {
+    // FIXME(generic_const_items): Add support for generic const items.
+    fn from_tcx(constant: clean::ConstantKind, tcx: TyCtxt<'_>) -> Self {
+        let expr = constant.expr(tcx);
+        let value = constant.value(tcx);
+        let is_literal = constant.is_literal(tcx);
+        Constant { expr, value, is_literal }
+    }
+}
+
 impl FromWithTcx<clean::AssocItemConstraint> for TypeBinding {
     fn from_tcx(constraint: clean::AssocItemConstraint, tcx: TyCtxt<'_>) -> Self {
         TypeBinding {
@@ -325,8 +335,8 @@ fn from_clean_item(item: clean::Item, tcx: TyCtxt<'_>) -> ItemEnum {
         TypeAliasItem(t) => ItemEnum::TypeAlias(t.into_tcx(tcx)),
         OpaqueTyItem(t) => ItemEnum::OpaqueTy(t.into_tcx(tcx)),
         // FIXME(generic_const_items): Add support for generic free consts
-        ConstantItem(_generics, t, c) => {
-            ItemEnum::Constant { type_: (*t).into_tcx(tcx), const_: c.into_tcx(tcx) }
+        ConstantItem(ci) => {
+            ItemEnum::Constant { type_: ci.type_.into_tcx(tcx), const_: ci.kind.into_tcx(tcx) }
         }
         MacroItem(m) => ItemEnum::Macro(m.source),
         ProcMacroItem(m) => ItemEnum::ProcMacro(m.into_tcx(tcx)),
@@ -341,8 +351,8 @@ fn from_clean_item(item: clean::Item, tcx: TyCtxt<'_>) -> ItemEnum {
             ItemEnum::AssocConst { type_: (*ty).into_tcx(tcx), default: None }
         }
         // FIXME(generic_const_items): Add support for generic associated consts.
-        AssocConstItem(_generics, ty, default) => {
-            ItemEnum::AssocConst { type_: (*ty).into_tcx(tcx), default: Some(default.expr(tcx)) }
+        AssocConstItem(ci) => {
+            ItemEnum::AssocConst { type_: ci.type_.into_tcx(tcx), default: Some(ci.kind.expr(tcx)) }
         }
         TyAssocTypeItem(g, b) => ItemEnum::AssocType {
             generics: g.into_tcx(tcx),
@@ -829,7 +839,8 @@ impl FromWithTcx<clean::OpaqueTy> for OpaqueTy {
 impl FromWithTcx<clean::Static> for Static {
     fn from_tcx(stat: clean::Static, tcx: TyCtxt<'_>) -> Self {
         Static {
-            type_: stat.type_.into_tcx(tcx),
+
+            type_: (*stat.type_).into_tcx(tcx),
             mutable: stat.mutability == ast::Mutability::Mut,
             expr: stat
                 .expr
diff --git a/src/librustdoc/passes/check_doc_test_visibility.rs b/src/librustdoc/passes/check_doc_test_visibility.rs
index 0437f5e5fd818..f97c417847359 100644
--- a/src/librustdoc/passes/check_doc_test_visibility.rs
+++ b/src/librustdoc/passes/check_doc_test_visibility.rs
@@ -62,7 +62,7 @@ pub(crate) fn should_have_doc_example(cx: &DocContext<'_>, item: &clean::Item) -
                 | clean::AssocTypeItem(..)
                 | clean::TypeAliasItem(_)
                 | clean::StaticItem(_)
-                | clean::ConstantItem(_, _, _)
+                | clean::ConstantItem(..)
                 | clean::ExternCrateItem { .. }
                 | clean::ImportItem(_)
                 | clean::PrimitiveItem(_)
diff --git a/src/librustdoc/visit.rs b/src/librustdoc/visit.rs
index b335dc5bd16b8..de836439be957 100644
--- a/src/librustdoc/visit.rs
+++ b/src/librustdoc/visit.rs
@@ -28,7 +28,7 @@ pub(crate) trait DocVisitor: Sized {
             | TypeAliasItem(_)
             | OpaqueTyItem(_)
             | StaticItem(_)
-            | ConstantItem(_, _, _)
+            | ConstantItem(..)
             | TraitAliasItem(_)
             | TyMethodItem(_)
             | MethodItem(_, _)