Auto merge of #100645 - notriddle:notriddle/rustdoc-diet-plan, r=GuillaumeGomez

rustdoc: strategic boxing to reduce the size of ItemKind and Type

The `Type` change redesigns `QPath` to box the entire data structure instead of boxing `self_type` and the `trait_`.

This reduces the size of several `ItemKind` variants, leaving `Impl` as the biggest variant. The `ItemKind` change boxes that variant's payload.

src/librustdoc/clean/auto_trait.rs

@@ -551,13 +551,15 @@ where
                 }
                 WherePredicate::EqPredicate { lhs, rhs } => {
                     match lhs {
-                        Type::QPath { ref assoc, ref self_type, ref trait_, .. } => {
+                        Type::QPath(box QPathData {
+                            ref assoc, ref self_type, ref trait_, ..
+                        }) => {
                             let ty = &*self_type;
                             let mut new_trait = trait_.clone();
 
                             if self.is_fn_trait(trait_) && assoc.name == sym::Output {
                                 ty_to_fn
-                                    .entry(*ty.clone())
+                                    .entry(ty.clone())
                                     .and_modify(|e| {
                                         *e = (e.0.clone(), Some(rhs.ty().unwrap().clone()))
                                     })
@@ -582,7 +584,7 @@ where
                                 // to 'T: Iterator<Item=u8>'
                                 GenericArgs::AngleBracketed { ref mut bindings, .. } => {
                                     bindings.push(TypeBinding {
-                                        assoc: *assoc.clone(),
+                                        assoc: assoc.clone(),
                                         kind: TypeBindingKind::Equality { term: rhs },
                                     });
                                 }
@@ -596,7 +598,7 @@ where
                                 }
                             }
 
-                            let bounds = ty_to_bounds.entry(*ty.clone()).or_default();
+                            let bounds = ty_to_bounds.entry(ty.clone()).or_default();
 
                             bounds.insert(GenericBound::TraitBound(
                                 PolyTrait { trait_: new_trait, generic_params: Vec::new() },
@@ -613,7 +615,7 @@ where
                             ));
                             // Avoid creating any new duplicate bounds later in the outer
                             // loop
-                            ty_to_traits.entry(*ty.clone()).or_default().insert(trait_.clone());
+                            ty_to_traits.entry(ty.clone()).or_default().insert(trait_.clone());
                         }
                         _ => panic!("Unexpected LHS {:?} for {:?}", lhs, item_def_id),
                     }

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);
@@ -672,7 +672,7 @@ fn filter_non_trait_generics(trait_did: DefId, mut g: clean::Generics) -> clean:
 
     g.where_predicates.retain(|pred| match pred {
         clean::WherePredicate::BoundPredicate {
-            ty: clean::QPath { self_type: box clean::Generic(ref s), trait_, .. },
+            ty: clean::QPath(box clean::QPathData { self_type: clean::Generic(ref s), trait_, .. }),
             bounds,
             ..
         } => !(bounds.is_empty() || *s == kw::SelfUpper && trait_.def_id() == trait_did),

src/librustdoc/clean/mod.rs

@@ -410,12 +410,12 @@ fn clean_projection<'tcx>(
         self_type.def_id(&cx.cache)
     };
     let should_show_cast = compute_should_show_cast(self_def_id, &trait_, &self_type);
-    Type::QPath {
+    Type::QPath(Box::new(QPathData {
-        assoc: Box::new(projection_to_path_segment(ty, cx)),
+        assoc: projection_to_path_segment(ty, cx),
         should_show_cast,
-        self_type: Box::new(self_type),
+        self_type,
         trait_,
-    }
+    }))
 }
 
 fn compute_should_show_cast(self_def_id: Option<DefId>, trait_: &Path, self_type: &Type) -> bool {
@@ -1182,7 +1182,7 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
                     .where_predicates
                     .drain_filter(|pred| match *pred {
                         WherePredicate::BoundPredicate {
-                            ty: QPath { ref assoc, ref self_type, ref trait_, .. },
+                            ty: QPath(box QPathData { ref assoc, ref self_type, ref trait_, .. }),
                             ..
                         } => {
                             if assoc.name != my_name {
@@ -1191,7 +1191,7 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
                             if trait_.def_id() != assoc_item.container_id(tcx) {
                                 return false;
                             }
-                            match **self_type {
+                            match *self_type {
                                 Generic(ref s) if *s == kw::SelfUpper => {}
                                 _ => return false,
                             }
@@ -1324,15 +1324,12 @@ fn clean_qpath<'tcx>(hir_ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> Type
             let self_def_id = DefId::local(qself.hir_id.owner.local_def_index);
             let self_type = clean_ty(qself, cx);
             let should_show_cast = compute_should_show_cast(Some(self_def_id), &trait_, &self_type);
-            Type::QPath {
+            Type::QPath(Box::new(QPathData {
-                assoc: Box::new(clean_path_segment(
+                assoc: clean_path_segment(p.segments.last().expect("segments were empty"), cx),
-                    p.segments.last().expect("segments were empty"),
-                    cx,
-                )),
                 should_show_cast,
-                self_type: Box::new(self_type),
+                self_type,
                 trait_,
-            }
+            }))
         }
         hir::QPath::TypeRelative(qself, segment) => {
             let ty = hir_ty_to_ty(cx.tcx, hir_ty);
@@ -1347,12 +1344,12 @@ fn clean_qpath<'tcx>(hir_ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> Type
             let self_def_id = res.opt_def_id();
             let self_type = clean_ty(qself, cx);
             let should_show_cast = compute_should_show_cast(self_def_id, &trait_, &self_type);
-            Type::QPath {
+            Type::QPath(Box::new(QPathData {
-                assoc: Box::new(clean_path_segment(segment, cx)),
+                assoc: clean_path_segment(segment, cx),
                 should_show_cast,
-                self_type: Box::new(self_type),
+                self_type,
                 trait_,
-            }
+            }))
         }
         hir::QPath::LangItem(..) => bug!("clean: requiring documentation of lang item"),
     }
@@ -1954,12 +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.
@@ -1550,13 +1550,7 @@ pub(crate) enum Type {
     BorrowedRef { lifetime: Option<Lifetime>, mutability: Mutability, type_: Box<Type> },
 
     /// A qualified path to an associated item: `<Type as Trait>::Name`
-    QPath {
+    QPath(Box<QPathData>),
-        assoc: Box<PathSegment>,
-        self_type: Box<Type>,
-        /// FIXME: compute this field on demand.
-        should_show_cast: bool,
-        trait_: Path,
-    },
 
     /// A type that is inferred: `_`
     Infer,
@@ -1654,8 +1648,8 @@ impl Type {
     }
 
     pub(crate) fn projection(&self) -> Option<(&Type, DefId, PathSegment)> {
-        if let QPath { self_type, trait_, assoc, .. } = self {
+        if let QPath(box QPathData { self_type, trait_, assoc, .. }) = self {
-            Some((self_type, trait_.def_id(), *assoc.clone()))
+            Some((self_type, trait_.def_id(), assoc.clone()))
         } else {
             None
         }
@@ -1679,7 +1673,7 @@ impl Type {
             Slice(..) => PrimitiveType::Slice,
             Array(..) => PrimitiveType::Array,
             RawPointer(..) => PrimitiveType::RawPointer,
-            QPath { ref self_type, .. } => return self_type.inner_def_id(cache),
+            QPath(box QPathData { ref self_type, .. }) => return self_type.inner_def_id(cache),
             Generic(_) | Infer | ImplTrait(_) => return None,
         };
         cache.and_then(|c| Primitive(t).def_id(c))
@@ -1693,6 +1687,15 @@ impl Type {
     }
 }
 
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
+pub(crate) struct QPathData {
+    pub assoc: PathSegment,
+    pub self_type: Type,
+    /// FIXME: compute this field on demand.
+    pub should_show_cast: bool,
+    pub trait_: Path,
+}
+
 /// A primitive (aka, builtin) type.
 ///
 /// This represents things like `i32`, `str`, etc.
@@ -2484,11 +2487,11 @@ mod size_asserts {
     // These are in alphabetical order, which is easy to maintain.
     static_assert_size!(Crate, 72); // frequently moved by-value
     static_assert_size!(DocFragment, 32);
-    static_assert_size!(GenericArg, 80);
+    static_assert_size!(GenericArg, 64);
     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, 72);
+    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/html/format.rs

@@ -1079,7 +1079,12 @@ fn fmt_type<'cx>(
                 write!(f, "impl {}", print_generic_bounds(bounds, cx))
             }
         }
-        clean::QPath { ref assoc, ref self_type, ref trait_, should_show_cast } => {
+        clean::QPath(box clean::QPathData {
+            ref assoc,
+            ref self_type,
+            ref trait_,
+            should_show_cast,
+        }) => {
             if f.alternate() {
                 if should_show_cast {
                     write!(f, "<{:#} as {:#}>::", self_type.print(cx), trait_.print(cx))?

src/librustdoc/html/render/mod.rs

@@ -2632,8 +2632,8 @@ fn collect_paths_for_type(first_ty: clean::Type, cache: &Cache) -> Vec<String> {
             clean::Type::BorrowedRef { type_, .. } => {
                 work.push_back(*type_);
             }
-            clean::Type::QPath { self_type, trait_, .. } => {
+            clean::Type::QPath(box clean::QPathData { self_type, trait_, .. }) => {
-                work.push_back(*self_type);
+                work.push_back(self_type);
                 process_path(trait_.def_id());
             }
             _ => {}

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)),
@@ -480,10 +480,10 @@ impl FromWithTcx<clean::Type> for Type {
                 mutable: mutability == ast::Mutability::Mut,
                 type_: Box::new((*type_).into_tcx(tcx)),
             },
-            QPath { assoc, self_type, trait_, .. } => Type::QualifiedPath {
+            QPath(box clean::QPathData { assoc, self_type, trait_, .. }) => Type::QualifiedPath {
                 name: assoc.name.to_string(),
                 args: Box::new(assoc.args.clone().into_tcx(tcx)),
-                self_type: Box::new((*self_type).into_tcx(tcx)),
+                self_type: Box::new(self_type.into_tcx(tcx)),
                 trait_: trait_.into_tcx(tcx),
             },
         }