Introduce const Trait (always-const trait bounds)

src/librustdoc/html/format.rs

@@ -449,8 +449,8 @@ impl clean::GenericBound {
                     hir::TraitBoundModifier::None => "",
                     hir::TraitBoundModifier::Maybe => "?",
                     hir::TraitBoundModifier::Negative => "!",
-                    // ~const is experimental; do not display those bounds in rustdoc
-                    hir::TraitBoundModifier::MaybeConst => "",
+                    // `const` and `~const` trait bounds are experimental; don't render them.
+                    hir::TraitBoundModifier::Const | hir::TraitBoundModifier::MaybeConst => "",
                 };
                 if f.alternate() {
                     write!(f, "{modifier_str}{ty:#}", ty = ty.print(cx))

src/librustdoc/json/conversions.rs

@@ -547,6 +547,9 @@ pub(crate) fn from_trait_bound_modifier(
         None => TraitBoundModifier::None,
         Maybe => TraitBoundModifier::Maybe,
         MaybeConst => TraitBoundModifier::MaybeConst,
+        // FIXME(const_trait_impl): Create rjt::TBM::Const and map to it once always-const bounds
+        // are less experimental.
+        Const => TraitBoundModifier::None,
         // FIXME(negative-bounds): This bound should be rendered negative, but
         // since that's experimental, maybe let's not add it to the rustdoc json
         // API just now...