Inline visiting of GenericArgs

Author: eggyal

compiler/rustc_macros/src/lib.rs

@@ -74,7 +74,7 @@ decl_derive!([TyEncodable] => serialize::type_encodable_derive);
 decl_derive!([MetadataDecodable] => serialize::meta_decodable_derive);
 decl_derive!([MetadataEncodable] => serialize::meta_encodable_derive);
 decl_derive!(
-    [TypeFoldable, attributes(type_foldable)] =>
+    [TypeFoldable, attributes(type_foldable, inline_traversals)] =>
     /// Derives `TypeFoldable` for the annotated `struct` or `enum` (`union` is not supported).
     ///
     /// Folds will produce a value of the same struct or enum variant as the input, with each field
@@ -97,10 +97,13 @@ decl_derive!(
     /// and
     ///
     /// `impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Bar<'tcx>`
+    ///
+    /// The annotated item may be decorated with an `#[inline_traversals]` attribute to cause the
+    /// generated folding method to be marked `#[inline]`.
     traversable::traversable_derive::<traversable::Foldable>
 );
 decl_derive!(
-    [TypeVisitable, attributes(type_visitable)] =>
+    [TypeVisitable, attributes(type_visitable, inline_traversals)] =>
     /// Derives `TypeVisitable` for the annotated `struct` or `enum` (`union` is not supported).
     ///
     /// Each field of the struct or enum variant will be visited (in definition order) using the
@@ -123,6 +126,9 @@ decl_derive!(
     /// and
     ///
     /// `impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for Bar<'tcx>`
+    ///
+    /// The annotated item may be decorated with an `#[inline_traversals]` attribute to cause the
+    /// generated folding method to be marked `#[inline]`.
     traversable::traversable_derive::<traversable::Visitable>
 );
 decl_derive!([Lift, attributes(lift)] => lift::lift_derive);

compiler/rustc_macros/src/traversable.rs

@@ -14,7 +14,7 @@ pub trait Traversable {
     fn arms(structure: &mut synstructure::Structure<'_>) -> TokenStream;
 
     /// The body of an implementation given the match `arms`.
-    fn impl_body(arms: impl ToTokens) -> TokenStream;
+    fn impl_body(arms: impl ToTokens, attrs: impl ToTokens) -> TokenStream;
 }
 
 impl Traversable for Foldable {
@@ -52,8 +52,9 @@ impl Traversable for Foldable {
             })
         })
     }
-    fn impl_body(arms: impl ToTokens) -> TokenStream {
+    fn impl_body(arms: impl ToTokens, attrs: impl ToTokens) -> TokenStream {
         quote! {
+            #attrs
             fn try_fold_with<__F: ::rustc_middle::ty::fold::FallibleTypeFolder<::rustc_middle::ty::TyCtxt<'tcx>>>(
                 self,
                 __folder: &mut __F
@@ -94,8 +95,9 @@ impl Traversable for Visitable {
             }
         })
     }
-    fn impl_body(arms: impl ToTokens) -> TokenStream {
+    fn impl_body(arms: impl ToTokens, attrs: impl ToTokens) -> TokenStream {
         quote! {
+            #attrs
             fn visit_with<__V: ::rustc_middle::ty::visit::TypeVisitor<::rustc_middle::ty::TyCtxt<'tcx>>>(
                 &self,
                 __visitor: &mut __V
@@ -122,5 +124,12 @@ pub fn traversable_derive<T: Traversable>(
     }
 
     let arms = T::arms(&mut structure);
-    structure.bound_impl(T::traversable(), T::impl_body(arms))
+    let attrs = structure
+        .ast()
+        .attrs
+        .iter()
+        .any(|attr| attr.path().is_ident("inline_traversals"))
+        .then_some(quote! { #[inline] });
+
+    structure.bound_impl(T::traversable(), T::impl_body(arms, attrs))
 }

compiler/rustc_middle/src/ty/generic_args.rs

@@ -48,6 +48,7 @@ const CONST_TAG: usize = 0b10;
 
 #[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord, HashStable)]
 #[derive(Clone, TypeFoldable, TypeVisitable)]
+#[inline_traversals]
 pub enum GenericArgKind<'tcx> {
     Lifetime(ty::Region<'tcx>),
     Type(Ty<'tcx>),
@@ -216,6 +217,7 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for GenericArg<'tcx> {
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for GenericArg<'tcx> {
+    #[inline]
     fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.unpack().visit_with(visitor)
     }