Rollup merge of #134321 - dtolnay:docassocconst, r=fmease

Hide `= _` as associated constant value inside impl blocks

Closes #134320.

### Before:

<img src="https://github.com/user-attachments/assets/19d28811-45d2-4563-9726-f40c6af411c6" width="300">&nbsp;<img src="https://github.com/user-attachments/assets/1ecf8764-97ce-47f0-87fa-3b174d2fc578" width="300">

### After:

<img src="https://github.com/user-attachments/assets/6408c4ca-b1c4-42e4-884b-248833a4865f" width="300">&nbsp;<img src="https://github.com/user-attachments/assets/df2f6981-16f6-409f-8abb-73c0a4a71d6b" width="300">

r? `@fmease`

src/librustdoc/clean/mod.rs

@@ -1222,14 +1222,16 @@ fn clean_trait_item<'tcx>(trait_item: &hir::TraitItem<'tcx>, cx: &mut DocContext
     let local_did = trait_item.owner_id.to_def_id();
     cx.with_param_env(local_did, |cx| {
         let inner = match trait_item.kind {
-            hir::TraitItemKind::Const(ty, Some(default)) => AssocConstItem(Box::new(Constant {
+            hir::TraitItemKind::Const(ty, Some(default)) => {
-                generics: enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx)),
+                ProvidedAssocConstItem(Box::new(Constant {
-                kind: ConstantKind::Local { def_id: local_did, body: default },
+                    generics: enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx)),
-                type_: clean_ty(ty, 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));
-                TyAssocConstItem(generics, Box::new(clean_ty(ty, cx)))
+                RequiredAssocConstItem(generics, Box::new(clean_ty(ty, cx)))
             }
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Provided(body)) => {
                 let m = clean_function(cx, sig, trait_item.generics, FunctionArgs::Body(body));
@@ -1237,7 +1239,7 @@ fn clean_trait_item<'tcx>(trait_item: &hir::TraitItem<'tcx>, cx: &mut DocContext
             }
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(names)) => {
                 let m = clean_function(cx, sig, trait_item.generics, FunctionArgs::Names(names));
-                TyMethodItem(m)
+                RequiredMethodItem(m)
             }
             hir::TraitItemKind::Type(bounds, Some(default)) => {
                 let generics = enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx));
@@ -1257,7 +1259,7 @@ fn clean_trait_item<'tcx>(trait_item: &hir::TraitItem<'tcx>, cx: &mut DocContext
             hir::TraitItemKind::Type(bounds, None) => {
                 let generics = enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx));
                 let bounds = bounds.iter().filter_map(|x| clean_generic_bound(x, cx)).collect();
-                TyAssocTypeItem(generics, bounds)
+                RequiredAssocTypeItem(generics, bounds)
             }
         };
         Item::from_def_id_and_parts(local_did, Some(trait_item.ident.name), inner, cx)
@@ -1271,7 +1273,7 @@ pub(crate) fn clean_impl_item<'tcx>(
     let local_did = impl_.owner_id.to_def_id();
     cx.with_param_env(local_did, |cx| {
         let inner = match impl_.kind {
-            hir::ImplItemKind::Const(ty, expr) => AssocConstItem(Box::new(Constant {
+            hir::ImplItemKind::Const(ty, expr) => ImplAssocConstItem(Box::new(Constant {
                 generics: clean_generics(impl_.generics, cx),
                 kind: ConstantKind::Local { def_id: local_did, body: expr },
                 type_: clean_ty(ty, cx),
@@ -1320,18 +1322,23 @@ pub(crate) fn clean_middle_assoc_item(assoc_item: &ty::AssocItem, cx: &mut DocCo
             );
             simplify::move_bounds_to_generic_parameters(&mut generics);
 
-            let provided = match assoc_item.container {
+            match assoc_item.container {
-                ty::AssocItemContainer::Impl => true,
+                ty::AssocItemContainer::Impl => ImplAssocConstItem(Box::new(Constant {
-                ty::AssocItemContainer::Trait => tcx.defaultness(assoc_item.def_id).has_value(),
-            };
-            if provided {
-                AssocConstItem(Box::new(Constant {
                     generics,
                     kind: ConstantKind::Extern { def_id: assoc_item.def_id },
                     type_: ty,
-                }))
+                })),
-            } else {
+                ty::AssocItemContainer::Trait => {
-                TyAssocConstItem(generics, Box::new(ty))
+                    if tcx.defaultness(assoc_item.def_id).has_value() {
+                        ProvidedAssocConstItem(Box::new(Constant {
+                            generics,
+                            kind: ConstantKind::Extern { def_id: assoc_item.def_id },
+                            type_: ty,
+                        }))
+                    } else {
+                        RequiredAssocConstItem(generics, Box::new(ty))
+                    }
+                }
             }
         }
         ty::AssocKind::Fn => {
@@ -1369,7 +1376,7 @@ pub(crate) fn clean_middle_assoc_item(assoc_item: &ty::AssocItem, cx: &mut DocCo
                 };
                 MethodItem(item, defaultness)
             } else {
-                TyMethodItem(item)
+                RequiredMethodItem(item)
             }
         }
         ty::AssocKind::Type => {
@@ -1486,7 +1493,7 @@ pub(crate) fn clean_middle_assoc_item(assoc_item: &ty::AssocItem, cx: &mut DocCo
                         bounds,
                     )
                 } else {
-                    TyAssocTypeItem(generics, bounds)
+                    RequiredAssocTypeItem(generics, bounds)
                 }
             } else {
                 AssocTypeItem(

src/librustdoc/clean/types.rs

@@ -545,14 +545,14 @@ impl Item {
     pub(crate) fn is_associated_type(&self) -> bool {
         matches!(self.kind, AssocTypeItem(..) | StrippedItem(box AssocTypeItem(..)))
     }
-    pub(crate) fn is_ty_associated_type(&self) -> bool {
+    pub(crate) fn is_required_associated_type(&self) -> bool {
-        matches!(self.kind, TyAssocTypeItem(..) | StrippedItem(box TyAssocTypeItem(..)))
+        matches!(self.kind, RequiredAssocTypeItem(..) | StrippedItem(box RequiredAssocTypeItem(..)))
     }
     pub(crate) fn is_associated_const(&self) -> bool {
-        matches!(self.kind, AssocConstItem(..) | StrippedItem(box AssocConstItem(..)))
+        matches!(self.kind, ProvidedAssocConstItem(..) | ImplAssocConstItem(..) | StrippedItem(box (ProvidedAssocConstItem(..) | ImplAssocConstItem(..))))
     }
-    pub(crate) fn is_ty_associated_const(&self) -> bool {
+    pub(crate) fn is_required_associated_const(&self) -> bool {
-        matches!(self.kind, TyAssocConstItem(..) | StrippedItem(box TyAssocConstItem(..)))
+        matches!(self.kind, RequiredAssocConstItem(..) | StrippedItem(box RequiredAssocConstItem(..)))
     }
     pub(crate) fn is_method(&self) -> bool {
         self.type_() == ItemType::Method
@@ -669,7 +669,9 @@ impl Item {
                     asyncness: hir::IsAsync::NotAsync,
                 }
             }
-            ItemKind::FunctionItem(_) | ItemKind::MethodItem(_, _) | ItemKind::TyMethodItem(_) => {
+            ItemKind::FunctionItem(_)
+            | ItemKind::MethodItem(_, _)
+            | ItemKind::RequiredMethodItem(_) => {
                 let def_id = self.def_id().unwrap();
                 build_fn_header(def_id, tcx, tcx.asyncness(def_id))
             }
@@ -699,8 +701,13 @@ impl Item {
             // Variants always inherit visibility
             VariantItem(..) | ImplItem(..) => return None,
             // Trait items inherit the trait's visibility
-            AssocConstItem(..) | TyAssocConstItem(..) | AssocTypeItem(..) | TyAssocTypeItem(..)
+            RequiredAssocConstItem(..)
-            | TyMethodItem(..) | MethodItem(..) => {
+            | ProvidedAssocConstItem(..)
+            | ImplAssocConstItem(..)
+            | AssocTypeItem(..)
+            | RequiredAssocTypeItem(..)
+            | RequiredMethodItem(..)
+            | MethodItem(..) => {
                 let assoc_item = tcx.associated_item(def_id);
                 let is_trait_item = match assoc_item.container {
                     ty::AssocItemContainer::Trait => true,
@@ -845,10 +852,10 @@ pub(crate) enum ItemKind {
     TraitAliasItem(TraitAlias),
     ImplItem(Box<Impl>),
     /// A required method in a trait declaration meaning it's only a function signature.
-    TyMethodItem(Box<Function>),
+    RequiredMethodItem(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.
+    /// Compared to [RequiredMethodItem], it also contains a method body.
     MethodItem(Box<Function>, Option<hir::Defaultness>),
     StructFieldItem(Type),
     VariantItem(Variant),
@@ -862,14 +869,16 @@ pub(crate) enum ItemKind {
     ProcMacroItem(ProcMacro),
     PrimitiveItem(PrimitiveType),
     /// A required associated constant in a trait declaration.
-    TyAssocConstItem(Generics, Box<Type>),
+    RequiredAssocConstItem(Generics, Box<Type>),
     ConstantItem(Box<Constant>),
-    /// An associated constant in a trait impl or a provided one in a trait declaration.
+    /// An associated constant in a trait declaration with provided default value.
-    AssocConstItem(Box<Constant>),
+    ProvidedAssocConstItem(Box<Constant>),
+    /// An associated constant in an inherent impl or trait impl.
+    ImplAssocConstItem(Box<Constant>),
     /// A required associated type in a trait declaration.
     ///
     /// The bounds may be non-empty if there is a `where` clause.
-    TyAssocTypeItem(Generics, Vec<GenericBound>),
+    RequiredAssocTypeItem(Generics, Vec<GenericBound>),
     /// An associated type in a trait impl or a provided one in a trait declaration.
     AssocTypeItem(Box<TypeAlias>, Vec<GenericBound>),
     /// An item that has been stripped by a rustdoc pass
@@ -900,7 +909,7 @@ impl ItemKind {
             | StaticItem(_)
             | ConstantItem(_)
             | TraitAliasItem(_)
-            | TyMethodItem(_)
+            | RequiredMethodItem(_)
             | MethodItem(_, _)
             | StructFieldItem(_)
             | ForeignFunctionItem(_, _)
@@ -909,9 +918,10 @@ impl ItemKind {
             | MacroItem(_)
             | ProcMacroItem(_)
             | PrimitiveItem(_)
-            | TyAssocConstItem(..)
+            | RequiredAssocConstItem(..)
-            | AssocConstItem(..)
+            | ProvidedAssocConstItem(..)
-            | TyAssocTypeItem(..)
+            | ImplAssocConstItem(..)
+            | RequiredAssocTypeItem(..)
             | AssocTypeItem(..)
             | StrippedItem(_)
             | KeywordItem => [].iter(),

src/librustdoc/fold.rs

@@ -82,7 +82,7 @@ pub(crate) trait DocFolder: Sized {
             | StaticItem(_)
             | ConstantItem(..)
             | TraitAliasItem(_)
-            | TyMethodItem(_)
+            | RequiredMethodItem(_)
             | MethodItem(_, _)
             | StructFieldItem(_)
             | ForeignFunctionItem(..)
@@ -91,9 +91,10 @@ pub(crate) trait DocFolder: Sized {
             | MacroItem(_)
             | ProcMacroItem(_)
             | PrimitiveItem(_)
-            | TyAssocConstItem(..)
+            | RequiredAssocConstItem(..)
-            | AssocConstItem(..)
+            | ProvidedAssocConstItem(..)
-            | TyAssocTypeItem(..)
+            | ImplAssocConstItem(..)
+            | RequiredAssocTypeItem(..)
             | AssocTypeItem(..)
             | KeywordItem => kind,
         }

src/librustdoc/formats/cache.rs

@@ -334,12 +334,13 @@ impl DocFolder for CacheBuilder<'_, '_> {
             clean::ExternCrateItem { .. }
             | clean::ImportItem(..)
             | clean::ImplItem(..)
-            | clean::TyMethodItem(..)
+            | clean::RequiredMethodItem(..)
             | clean::MethodItem(..)
             | clean::StructFieldItem(..)
-            | clean::TyAssocConstItem(..)
+            | clean::RequiredAssocConstItem(..)
-            | clean::AssocConstItem(..)
+            | clean::ProvidedAssocConstItem(..)
-            | clean::TyAssocTypeItem(..)
+            | clean::ImplAssocConstItem(..)
+            | clean::RequiredAssocTypeItem(..)
             | clean::AssocTypeItem(..)
             | clean::StrippedItem(..)
             | clean::KeywordItem => {
@@ -443,15 +444,17 @@ fn add_item_to_search_index(tcx: TyCtxt<'_>, cache: &mut Cache, item: &clean::It
     let item_def_id = item.item_id.as_def_id().unwrap();
     let (parent_did, parent_path) = match item.kind {
         clean::StrippedItem(..) => return,
-        clean::AssocConstItem(..) | clean::AssocTypeItem(..)
+        clean::ProvidedAssocConstItem(..)
+        | clean::ImplAssocConstItem(..)
+        | clean::AssocTypeItem(..)
             if cache.parent_stack.last().is_some_and(|parent| parent.is_trait_impl()) =>
         {
             // skip associated items in trait impls
             return;
         }
-        clean::TyMethodItem(..)
+        clean::RequiredMethodItem(..)
-        | clean::TyAssocConstItem(..)
+        | clean::RequiredAssocConstItem(..)
-        | clean::TyAssocTypeItem(..)
+        | clean::RequiredAssocTypeItem(..)
         | clean::StructFieldItem(..)
         | clean::VariantItem(..) => {
             // Don't index if containing module is stripped (i.e., private),
@@ -467,7 +470,10 @@ fn add_item_to_search_index(tcx: TyCtxt<'_>, cache: &mut Cache, item: &clean::It
             let parent_path = &cache.stack[..cache.stack.len() - 1];
             (Some(parent_did), parent_path)
         }
-        clean::MethodItem(..) | clean::AssocConstItem(..) | clean::AssocTypeItem(..) => {
+        clean::MethodItem(..)
+        | clean::ProvidedAssocConstItem(..)
+        | clean::ImplAssocConstItem(..)
+        | clean::AssocTypeItem(..) => {
             let last = cache.parent_stack.last().expect("parent_stack is empty 2");
             let parent_did = match last {
                 // impl Trait for &T { fn method(self); }

src/librustdoc/formats/item_type.rs

@@ -88,7 +88,7 @@ impl<'a> From<&'a clean::Item> for ItemType {
             clean::ConstantItem(..) => ItemType::Constant,
             clean::TraitItem(..) => ItemType::Trait,
             clean::ImplItem(..) => ItemType::Impl,
-            clean::TyMethodItem(..) => ItemType::TyMethod,
+            clean::RequiredMethodItem(..) => ItemType::TyMethod,
             clean::MethodItem(..) => ItemType::Method,
             clean::StructFieldItem(..) => ItemType::StructField,
             clean::VariantItem(..) => ItemType::Variant,
@@ -96,8 +96,10 @@ impl<'a> From<&'a clean::Item> for ItemType {
             clean::ForeignStaticItem(..) => ItemType::Static,     // no ForeignStatic
             clean::MacroItem(..) => ItemType::Macro,
             clean::PrimitiveItem(..) => ItemType::Primitive,
-            clean::TyAssocConstItem(..) | clean::AssocConstItem(..) => ItemType::AssocConst,
+            clean::RequiredAssocConstItem(..)
-            clean::TyAssocTypeItem(..) | clean::AssocTypeItem(..) => ItemType::AssocType,
+            | clean::ProvidedAssocConstItem(..)
+            | clean::ImplAssocConstItem(..) => ItemType::AssocConst,
+            clean::RequiredAssocTypeItem(..) | clean::AssocTypeItem(..) => ItemType::AssocType,
             clean::ForeignTypeItem => ItemType::ForeignType,
             clean::KeywordItem => ItemType::Keyword,
             clean::TraitAliasItem(..) => ItemType::TraitAlias,

src/librustdoc/html/render/mod.rs

@@ -836,12 +836,23 @@ fn assoc_href_attr(it: &clean::Item, link: AssocItemLink<'_>, cx: &Context<'_>)
     href.map(|href| format!(" href=\"{href}\"")).unwrap_or_default()
 }
 
+#[derive(Debug)]
+enum AssocConstValue<'a> {
+    // In trait definitions, it is relevant for the public API whether an
+    // associated constant comes with a default value, so even if we cannot
+    // render its value, the presence of a value must be shown using `= _`.
+    TraitDefault(&'a clean::ConstantKind),
+    // In impls, there is no need to show `= _`.
+    Impl(&'a clean::ConstantKind),
+    None,
+}
+
 fn assoc_const(
     w: &mut Buffer,
     it: &clean::Item,
     generics: &clean::Generics,
     ty: &clean::Type,
-    default: Option<&clean::ConstantKind>,
+    value: AssocConstValue<'_>,
     link: AssocItemLink<'_>,
     indent: usize,
     cx: &Context<'_>,
@@ -857,15 +868,20 @@ fn assoc_const(
         generics = generics.print(cx),
         ty = ty.print(cx),
     );
-    if let Some(default) = default {
+    if let AssocConstValue::TraitDefault(konst) | AssocConstValue::Impl(konst) = value {
-        w.write_str(" = ");
-
         // FIXME: `.value()` uses `clean::utils::format_integer_with_underscore_sep` under the
         //        hood which adds noisy underscores and a type suffix to number literals.
         //        This hurts readability in this context especially when more complex expressions
         //        are involved and it doesn't add much of value.
         //        Find a way to print constants here without all that jazz.
-        write!(w, "{}", Escape(&default.value(tcx).unwrap_or_else(|| default.expr(tcx))));
+        let repr = konst.value(tcx).unwrap_or_else(|| konst.expr(tcx));
+        if match value {
+            AssocConstValue::TraitDefault(_) => true, // always show
+            AssocConstValue::Impl(_) => repr != "_",  // show if there is a meaningful value to show
+            AssocConstValue::None => unreachable!(),
+        } {
+            write!(w, " = {}", Escape(&repr));
+        }
     }
     write!(w, "{}", print_where_clause(generics, cx, indent, Ending::NoNewline));
 }
@@ -1076,33 +1092,43 @@ fn render_assoc_item(
 ) {
     match &item.kind {
         clean::StrippedItem(..) => {}
-        clean::TyMethodItem(m) => {
+        clean::RequiredMethodItem(m) => {
             assoc_method(w, item, &m.generics, &m.decl, link, parent, cx, render_mode)
         }
         clean::MethodItem(m, _) => {
             assoc_method(w, item, &m.generics, &m.decl, link, parent, cx, render_mode)
         }
-        clean::TyAssocConstItem(generics, ty) => assoc_const(
+        clean::RequiredAssocConstItem(generics, ty) => assoc_const(
             w,
             item,
             generics,
             ty,
-            None,
+            AssocConstValue::None,
             link,
             if parent == ItemType::Trait { 4 } else { 0 },
             cx,
         ),
-        clean::AssocConstItem(ci) => assoc_const(
+        clean::ProvidedAssocConstItem(ci) => assoc_const(
             w,
             item,
             &ci.generics,
             &ci.type_,
-            Some(&ci.kind),
+            AssocConstValue::TraitDefault(&ci.kind),
             link,
             if parent == ItemType::Trait { 4 } else { 0 },
             cx,
         ),
-        clean::TyAssocTypeItem(ref generics, ref bounds) => assoc_type(
+        clean::ImplAssocConstItem(ci) => assoc_const(
+            w,
+            item,
+            &ci.generics,
+            &ci.type_,
+            AssocConstValue::Impl(&ci.kind),
+            link,
+            if parent == ItemType::Trait { 4 } else { 0 },
+            cx,
+        ),
+        clean::RequiredAssocTypeItem(ref generics, ref bounds) => assoc_type(
             w,
             item,
             generics,
@@ -1384,7 +1410,7 @@ fn render_deref_methods(
 fn should_render_item(item: &clean::Item, deref_mut_: bool, tcx: TyCtxt<'_>) -> bool {
     let self_type_opt = match item.kind {
         clean::MethodItem(ref method, _) => method.decl.receiver_type(),
-        clean::TyMethodItem(ref method) => method.decl.receiver_type(),
+        clean::RequiredMethodItem(ref method) => method.decl.receiver_type(),
         _ => None,
     };
 
@@ -1660,7 +1686,7 @@ fn render_impl(
             write!(w, "<details class=\"toggle{method_toggle_class}\" open><summary>");
         }
         match &item.kind {
-            clean::MethodItem(..) | clean::TyMethodItem(_) => {
+            clean::MethodItem(..) | clean::RequiredMethodItem(_) => {
                 // Only render when the method is not static or we allow static methods
                 if render_method_item {
                     let id = cx.derive_id(format!("{item_type}.{name}"));
@@ -1690,7 +1716,7 @@ fn render_impl(
                     w.write_str("</h4></section>");
                 }
             }
-            clean::TyAssocConstItem(ref generics, ref ty) => {
+            clean::RequiredAssocConstItem(ref generics, ref 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}\">");
@@ -1705,14 +1731,14 @@ fn render_impl(
                     item,
                     generics,
                     ty,
-                    None,
+                    AssocConstValue::None,
                     link.anchor(if trait_.is_some() { &source_id } else { &id }),
                     0,
                     cx,
                 );
                 w.write_str("</h4></section>");
             }
-            clean::AssocConstItem(ci) => {
+            clean::ProvidedAssocConstItem(ci) | clean::ImplAssocConstItem(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}\">");
@@ -1727,14 +1753,18 @@ fn render_impl(
                     item,
                     &ci.generics,
                     &ci.type_,
-                    Some(&ci.kind),
+                    match item.kind {
+                        clean::ProvidedAssocConstItem(_) => AssocConstValue::TraitDefault(&ci.kind),
+                        clean::ImplAssocConstItem(_) => AssocConstValue::Impl(&ci.kind),
+                        _ => unreachable!(),
+                    },
                     link.anchor(if trait_.is_some() { &source_id } else { &id }),
                     0,
                     cx,
                 );
                 w.write_str("</h4></section>");
             }
-            clean::TyAssocTypeItem(ref generics, ref bounds) => {
+            clean::RequiredAssocTypeItem(ref generics, ref bounds) => {
                 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}\">");
@@ -1809,11 +1839,13 @@ fn render_impl(
     if !impl_.is_negative_trait_impl() {
         for trait_item in &impl_.items {
             match trait_item.kind {
-                clean::MethodItem(..) | clean::TyMethodItem(_) => methods.push(trait_item),
+                clean::MethodItem(..) | clean::RequiredMethodItem(_) => methods.push(trait_item),
-                clean::TyAssocTypeItem(..) | clean::AssocTypeItem(..) => {
+                clean::RequiredAssocTypeItem(..) | clean::AssocTypeItem(..) => {
                     assoc_types.push(trait_item)
                 }
-                clean::TyAssocConstItem(..) | clean::AssocConstItem(_) => {
+                clean::RequiredAssocConstItem(..)
+                | clean::ProvidedAssocConstItem(_)
+                | clean::ImplAssocConstItem(_) => {
                     // We render it directly since they're supposed to come first.
                     doc_impl_item(
                         &mut default_impl_items,

src/librustdoc/html/render/print_item.rs

@@ -651,9 +651,11 @@ fn item_function(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, f: &clean::
 fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Trait) {
     let tcx = cx.tcx();
     let bounds = bounds(&t.bounds, false, cx);
-    let required_types = t.items.iter().filter(|m| m.is_ty_associated_type()).collect::<Vec<_>>();
+    let required_types =
+        t.items.iter().filter(|m| m.is_required_associated_type()).collect::<Vec<_>>();
     let provided_types = t.items.iter().filter(|m| m.is_associated_type()).collect::<Vec<_>>();
-    let required_consts = t.items.iter().filter(|m| m.is_ty_associated_const()).collect::<Vec<_>>();
+    let required_consts =
+        t.items.iter().filter(|m| m.is_required_associated_const()).collect::<Vec<_>>();
     let provided_consts = t.items.iter().filter(|m| m.is_associated_const()).collect::<Vec<_>>();
     let required_methods = t.items.iter().filter(|m| m.is_ty_method()).collect::<Vec<_>>();
     let provided_methods = t.items.iter().filter(|m| m.is_method()).collect::<Vec<_>>();

src/librustdoc/html/render/search_index.rs

@@ -837,7 +837,7 @@ pub(crate) fn get_function_type_for_search(
         clean::ForeignFunctionItem(ref f, _)
         | clean::FunctionItem(ref f)
         | clean::MethodItem(ref f, _)
-        | clean::TyMethodItem(ref f) => {
+        | clean::RequiredMethodItem(ref f) => {
             get_fn_inputs_and_outputs(f, tcx, impl_or_trait_generics, cache)
         }
         _ => return None,
@@ -1207,10 +1207,11 @@ fn simplify_fn_type<'a, 'tcx>(
                 && let Type::Path { path } = arg
                 && let def_id = path.def_id()
                 && let Some(trait_) = cache.traits.get(&def_id)
-                && trait_.items.iter().any(|at| at.is_ty_associated_type())
+                && trait_.items.iter().any(|at| at.is_required_associated_type())
             {
                 for assoc_ty in &trait_.items {
-                    if let clean::ItemKind::TyAssocTypeItem(_generics, bounds) = &assoc_ty.kind
+                    if let clean::ItemKind::RequiredAssocTypeItem(_generics, bounds) =
+                        &assoc_ty.kind
                         && let Some(name) = assoc_ty.name
                     {
                         let idx = -isize::try_from(rgen.len() + 1).unwrap();

src/librustdoc/html/render/sidebar.rs

@@ -282,10 +282,10 @@ fn sidebar_trait<'a>(
         res
     }
 
-    let req_assoc = filter_items(&t.items, |m| m.is_ty_associated_type(), "associatedtype");
+    let req_assoc = filter_items(&t.items, |m| m.is_required_associated_type(), "associatedtype");
     let prov_assoc = filter_items(&t.items, |m| m.is_associated_type(), "associatedtype");
     let req_assoc_const =
-        filter_items(&t.items, |m| m.is_ty_associated_const(), "associatedconstant");
+        filter_items(&t.items, |m| m.is_required_associated_const(), "associatedconstant");
     let prov_assoc_const =
         filter_items(&t.items, |m| m.is_associated_const(), "associatedconstant");
     let req_method = filter_items(&t.items, |m| m.is_ty_method(), "tymethod");

src/librustdoc/json/conversions.rs

@@ -319,7 +319,9 @@ fn from_clean_item(item: clean::Item, renderer: &JsonRenderer<'_>) -> ItemEnum {
         TraitItem(t) => ItemEnum::Trait((*t).into_json(renderer)),
         TraitAliasItem(t) => ItemEnum::TraitAlias(t.into_json(renderer)),
         MethodItem(m, _) => ItemEnum::Function(from_function(m, true, header.unwrap(), renderer)),
-        TyMethodItem(m) => ItemEnum::Function(from_function(m, false, header.unwrap(), renderer)),
+        RequiredMethodItem(m) => {
+            ItemEnum::Function(from_function(m, false, header.unwrap(), renderer))
+        }
         ImplItem(i) => ItemEnum::Impl((*i).into_json(renderer)),
         StaticItem(s) => ItemEnum::Static(convert_static(s, rustc_hir::Safety::Safe, renderer)),
         ForeignStaticItem(s, safety) => ItemEnum::Static(convert_static(s, safety, renderer)),
@@ -339,15 +341,15 @@ fn from_clean_item(item: clean::Item, renderer: &JsonRenderer<'_>) -> ItemEnum {
             })
         }
         // FIXME(generic_const_items): Add support for generic associated consts.
-        TyAssocConstItem(_generics, ty) => {
+        RequiredAssocConstItem(_generics, ty) => {
             ItemEnum::AssocConst { type_: (*ty).into_json(renderer), value: None }
         }
         // FIXME(generic_const_items): Add support for generic associated consts.
-        AssocConstItem(ci) => ItemEnum::AssocConst {
+        ProvidedAssocConstItem(ci) | ImplAssocConstItem(ci) => ItemEnum::AssocConst {
             type_: ci.type_.into_json(renderer),
             value: Some(ci.kind.expr(renderer.tcx)),
         },
-        TyAssocTypeItem(g, b) => ItemEnum::AssocType {
+        RequiredAssocTypeItem(g, b) => ItemEnum::AssocType {
             generics: g.into_json(renderer),
             bounds: b.into_json(renderer),
             type_: None,

src/librustdoc/passes/check_doc_test_visibility.rs

@@ -72,10 +72,11 @@ pub(crate) fn should_have_doc_example(cx: &DocContext<'_>, item: &clean::Item) -
                 | clean::ForeignFunctionItem(..)
                 | clean::ForeignStaticItem(..)
                 | clean::ForeignTypeItem
-                | clean::AssocConstItem(..)
                 | clean::AssocTypeItem(..)
-                | clean::TyAssocConstItem(..)
+                | clean::RequiredAssocConstItem(..)
-                | clean::TyAssocTypeItem(..)
+                | clean::ProvidedAssocConstItem(..)
+                | clean::ImplAssocConstItem(..)
+                | clean::RequiredAssocTypeItem(..)
                 // check for trait impl
                 | clean::ImplItem(box clean::Impl { trait_: Some(_), .. })
         )

src/librustdoc/passes/propagate_stability.rs

@@ -67,11 +67,12 @@ impl DocFolder for StabilityPropagator<'_, '_> {
                     // Don't inherit the parent's stability for these items, because they
                     // are potentially accessible even if the parent is more unstable.
                     ItemKind::ImplItem(..)
-                    | ItemKind::TyMethodItem(..)
+                    | ItemKind::RequiredMethodItem(..)
                     | ItemKind::MethodItem(..)
-                    | ItemKind::TyAssocConstItem(..)
+                    | ItemKind::RequiredAssocConstItem(..)
-                    | ItemKind::AssocConstItem(..)
+                    | ItemKind::ProvidedAssocConstItem(..)
-                    | ItemKind::TyAssocTypeItem(..)
+                    | ItemKind::ImplAssocConstItem(..)
+                    | ItemKind::RequiredAssocTypeItem(..)
                     | ItemKind::AssocTypeItem(..)
                     | ItemKind::PrimitiveItem(..)
                     | ItemKind::KeywordItem => own_stability,

src/librustdoc/passes/stripper.rs

@@ -79,7 +79,10 @@ impl DocFolder for Stripper<'_, '_> {
                 }
             }
 
-            clean::MethodItem(..) | clean::AssocConstItem(..) | clean::AssocTypeItem(..) => {
+            clean::MethodItem(..)
+            | clean::ProvidedAssocConstItem(..)
+            | clean::ImplAssocConstItem(..)
+            | clean::AssocTypeItem(..) => {
                 let item_id = i.item_id;
                 if item_id.is_local()
                     && !self.effective_visibilities.is_reachable(self.tcx, item_id.expect_def_id())
@@ -118,7 +121,9 @@ impl DocFolder for Stripper<'_, '_> {
             clean::ImplItem(..) => {}
 
             // tymethods etc. have no control over privacy
-            clean::TyMethodItem(..) | clean::TyAssocConstItem(..) | clean::TyAssocTypeItem(..) => {}
+            clean::RequiredMethodItem(..)
+            | clean::RequiredAssocConstItem(..)
+            | clean::RequiredAssocTypeItem(..) => {}
 
             // Proc-macros are always public
             clean::ProcMacroItem(..) => {}

src/librustdoc/visit.rs

@@ -35,7 +35,7 @@ pub(crate) trait DocVisitor<'a>: Sized {
             | StaticItem(_)
             | ConstantItem(..)
             | TraitAliasItem(_)
-            | TyMethodItem(_)
+            | RequiredMethodItem(_)
             | MethodItem(_, _)
             | StructFieldItem(_)
             | ForeignFunctionItem(..)
@@ -44,9 +44,10 @@ pub(crate) trait DocVisitor<'a>: Sized {
             | MacroItem(_)
             | ProcMacroItem(_)
             | PrimitiveItem(_)
-            | TyAssocConstItem(..)
+            | RequiredAssocConstItem(..)
-            | AssocConstItem(..)
+            | ProvidedAssocConstItem(..)
-            | TyAssocTypeItem(..)
+            | ImplAssocConstItem(..)
+            | RequiredAssocTypeItem(..)
             | AssocTypeItem(..)
             | KeywordItem => {}
         }

tests/rustdoc/assoc-consts-underscore.rs

@@ -0,0 +1,30 @@
+pub struct Struct {
+    _private: (),
+}
+
+pub trait Trait {
+    //@ has assoc_consts_underscore/trait.Trait.html '//pre[@class="rust item-decl"]' \
+    //      'const REQUIRED: Struct;'
+    //@ !has - '//*[@id="associatedconstant.REQUIRED"]' 'const REQUIRED: Struct = _'
+    //@ has - '//*[@id="associatedconstant.REQUIRED"]' 'const REQUIRED: Struct'
+    const REQUIRED: Struct;
+    //@ has - '//pre[@class="rust item-decl"]' 'const OPTIONAL: Struct = _;'
+    //@ has - '//*[@id="associatedconstant.OPTIONAL"]' 'const OPTIONAL: Struct = _'
+    const OPTIONAL: Struct = Struct { _private: () };
+}
+
+impl Trait for Struct {
+    //@ !has assoc_consts_underscore/struct.Struct.html '//*[@id="associatedconstant.REQUIRED"]' \
+    //      'const REQUIRED: Struct = _'
+    //@ has - '//*[@id="associatedconstant.REQUIRED"]' 'const REQUIRED: Struct'
+    const REQUIRED: Struct = Struct { _private: () };
+    //@ !has - '//*[@id="associatedconstant.OPTIONAL"]' 'const OPTIONAL: Struct = _'
+    //@ has - '//*[@id="associatedconstant.OPTIONAL"]' 'const OPTIONAL: Struct'
+    const OPTIONAL: Struct = Struct { _private: () };
+}
+
+impl Struct {
+    //@ !has - '//*[@id="associatedconstant.INHERENT"]' 'const INHERENT: Struct = _'
+    //@ has - '//*[@id="associatedconstant.INHERENT"]' 'const INHERENT: Struct'
+    pub const INHERENT: Struct = Struct { _private: () };
+}

tests/rustdoc/bold-tag-101743.rs

@@ -14,6 +14,6 @@ impl<const B: Word> Repr<B> {
     // If we change back to rendering the value of consts, check this doesn't add
     // a <b> tag, but escapes correctly
 
-    //@ has foo/struct.Repr.html '//section[@id="associatedconstant.BASE"]/h4' '= _'
+    //@ !has foo/struct.Repr.html '//section[@id="associatedconstant.BASE"]/h4' '='
     pub const BASE: IBig = base_as_ibig::<B>();
 }