Auto merge of rust-lang#117896 - eggyal:traversables-1-tidy-up, r=<try>

TypeFoldable/TypeVisitable tidy up

I'm breaking rust-lang#117726 into more manageable, logical chunks.  This is the first of those, and just makes some minor/tidying refactors in preparation for the chunks to follow.

r? types

Author: bors

compiler/rustc_macros/src/lib.rs

@@ -23,8 +23,7 @@ mod newtype;
 mod query;
 mod serialize;
 mod symbols;
-mod type_foldable;
-mod type_visitable;
+mod traversable;
 
 // Reads the rust version (e.g. "1.75.0") from the CFG_RELEASE env var and
 // produces a `RustcVersion` literal containing that version (e.g.
@@ -81,22 +80,53 @@ decl_derive!(
     [TypeFoldable, attributes(type_foldable)] =>
     /// Derives `TypeFoldable` for the annotated `struct` or `enum` (`union` is not supported).
     ///
-    /// The fold will produce a value of the same struct or enum variant as the input, with
-    /// each field respectively folded using the `TypeFoldable` implementation for its type.
-    /// However, if a field of a struct or an enum variant is annotated with
-    /// `#[type_foldable(identity)]` then that field will retain its incumbent value (and its
-    /// type is not required to implement `TypeFoldable`).
-    type_foldable::type_foldable_derive
+    /// Folds will produce a value of the same struct or enum variant as the input, with each field
+    /// respectively folded (in definition order) using the `TypeFoldable` implementation for its
+    /// type. However, if a field of a struct or of an enum variant is annotated with
+    /// `#[type_foldable(identity)]` then that field will retain its incumbent value (and its type
+    /// is not required to implement `TypeFoldable`). However use of this attribute is dangerous
+    /// and should be used with extreme caution: should the type of the annotated field contain
+    /// (now or in the future) a type that is of interest to a folder, it will not get folded (which
+    /// may result in unexpected, hard-to-track bugs that could result in unsoundness).
+    ///
+    /// If the annotated item has a `'tcx` lifetime parameter, then that will be used as the
+    /// lifetime for the type context/interner; otherwise the lifetime of the type context/interner
+    /// will be unrelated to the annotated type. It therefore matters how any lifetime parameters of
+    /// the annotated type are named. For example, deriving `TypeFoldable` for both `Foo<'a>` and
+    /// `Bar<'tcx>` will respectively produce:
+    ///
+    /// `impl<'a, 'tcx> TypeFoldable<TyCtxt<'tcx>> for Foo<'a>`
+    ///
+    /// and
+    ///
+    /// `impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Bar<'tcx>`
+    traversable::traversable_derive::<traversable::Foldable>
 );
 decl_derive!(
     [TypeVisitable, attributes(type_visitable)] =>
     /// 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
-    /// `TypeVisitable` implementation for its type. However, if a field of a struct or an enum
-    /// variant is annotated with `#[type_visitable(ignore)]` then that field will not be
-    /// visited (and its type is not required to implement `TypeVisitable`).
-    type_visitable::type_visitable_derive
+    /// Each field of the struct or enum variant will be visited (in definition order) using the
+    /// `TypeVisitable` implementation for its type. However, if a field of a struct or of an enum
+    /// variant is annotated with `#[type_visitable(ignore)]` then that field will not be visited
+    /// (and its type is not required to implement `TypeVisitable`). However use of this attribute
+    /// is dangerous and should be used with extreme caution: should the type of the annotated
+    /// field (now or in the future) a type that is of interest to a visitor, it will not get
+    /// visited (which may result in unexpected, hard-to-track bugs that could result in
+    /// unsoundness).
+    ///
+    /// If the annotated item has a `'tcx` lifetime parameter, then that will be used as the
+    /// lifetime for the type context/interner; otherwise the lifetime of the type context/interner
+    /// will be unrelated to the annotated type. It therefore matters how any lifetime parameters of
+    /// the annotated type are named. For example, deriving `TypeVisitable` for both `Foo<'a>` and
+    /// `Bar<'tcx>` will respectively produce:
+    ///
+    /// `impl<'a, 'tcx> TypeVisitable<TyCtxt<'tcx>> for Foo<'a>`
+    ///
+    /// and
+    ///
+    /// `impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for Bar<'tcx>`
+    traversable::traversable_derive::<traversable::Visitable>
 );
 decl_derive!([Lift, attributes(lift)] => lift::lift_derive);
 decl_derive!(

compiler/rustc_macros/src/traversable.rs

@@ -0,0 +1,126 @@
+use proc_macro2::TokenStream;
+use quote::{quote, ToTokens};
+use syn::parse_quote;
+
+pub struct Foldable;
+pub struct Visitable;
+
+/// An abstraction over traversable traits.
+pub trait Traversable {
+    /// The trait that this `Traversable` represents.
+    fn traversable() -> TokenStream;
+
+    /// The `match` arms for a traversal of this type.
+    fn arms(structure: &mut synstructure::Structure<'_>) -> TokenStream;
+
+    /// The body of an implementation given the match `arms`.
+    fn impl_body(arms: impl ToTokens) -> TokenStream;
+}
+
+impl Traversable for Foldable {
+    fn traversable() -> TokenStream {
+        quote! { ::rustc_middle::ty::fold::TypeFoldable<::rustc_middle::ty::TyCtxt<'tcx>> }
+    }
+    fn arms(structure: &mut synstructure::Structure<'_>) -> TokenStream {
+        structure.each_variant(|vi| {
+            let bindings = vi.bindings();
+            vi.construct(|_, index| {
+                let bind = &bindings[index];
+
+                let mut fixed = false;
+
+                // retain value of fields with #[type_foldable(identity)]
+                bind.ast().attrs.iter().for_each(|x| {
+                    if !x.path().is_ident("type_foldable") {
+                        return;
+                    }
+                    let _ = x.parse_nested_meta(|nested| {
+                        if nested.path.is_ident("identity") {
+                            fixed = true;
+                        }
+                        Ok(())
+                    });
+                });
+
+                if fixed {
+                    bind.to_token_stream()
+                } else {
+                    quote! {
+                        ::rustc_middle::ty::fold::TypeFoldable::try_fold_with(#bind, __folder)?
+                    }
+                }
+            })
+        })
+    }
+    fn impl_body(arms: impl ToTokens) -> TokenStream {
+        quote! {
+            fn try_fold_with<__F: ::rustc_middle::ty::fold::FallibleTypeFolder<::rustc_middle::ty::TyCtxt<'tcx>>>(
+                self,
+                __folder: &mut __F
+            ) -> ::core::result::Result<Self, __F::Error> {
+                ::core::result::Result::Ok(match self { #arms })
+            }
+        }
+    }
+}
+
+impl Traversable for Visitable {
+    fn traversable() -> TokenStream {
+        quote! { ::rustc_middle::ty::visit::TypeVisitable<::rustc_middle::ty::TyCtxt<'tcx>> }
+    }
+    fn arms(structure: &mut synstructure::Structure<'_>) -> TokenStream {
+        // ignore fields with #[type_visitable(ignore)]
+        structure.filter(|bi| {
+            let mut ignored = false;
+
+            bi.ast().attrs.iter().for_each(|attr| {
+                if !attr.path().is_ident("type_visitable") {
+                    return;
+                }
+                let _ = attr.parse_nested_meta(|nested| {
+                    if nested.path.is_ident("ignore") {
+                        ignored = true;
+                    }
+                    Ok(())
+                });
+            });
+
+            !ignored
+        });
+
+        structure.each(|bind| {
+            quote! {
+                ::rustc_middle::ty::visit::TypeVisitable::visit_with(#bind, __visitor)?;
+            }
+        })
+    }
+    fn impl_body(arms: impl ToTokens) -> TokenStream {
+        quote! {
+            fn visit_with<__V: ::rustc_middle::ty::visit::TypeVisitor<::rustc_middle::ty::TyCtxt<'tcx>>>(
+                &self,
+                __visitor: &mut __V
+            ) -> ::std::ops::ControlFlow<__V::BreakTy> {
+                match self { #arms }
+                ::std::ops::ControlFlow::Continue(())
+            }
+        }
+    }
+}
+
+pub fn traversable_derive<T: Traversable>(
+    mut structure: synstructure::Structure<'_>,
+) -> TokenStream {
+    if let syn::Data::Union(_) = structure.ast().data {
+        panic!("cannot derive on union")
+    }
+
+    structure.add_bounds(synstructure::AddBounds::Generics);
+    structure.bind_with(|_| synstructure::BindStyle::Move);
+
+    if !structure.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
+        structure.add_impl_generic(parse_quote! { 'tcx });
+    }
+
+    let arms = T::arms(&mut structure);
+    structure.bound_impl(T::traversable(), T::impl_body(arms))
+}

compiler/rustc_macros/src/type_foldable.rs

@@ -401,14 +401,16 @@ pub enum ClosureOutlivesSubject<'tcx> {
 /// This abstraction is necessary because the type may include `ReVar` regions,
 /// which is what we use internally within NLL code, and they can't be used in
 /// a query response.
-///
-/// DO NOT implement `TypeVisitable` or `TypeFoldable` traits, because this
-/// type is not recognized as a binder for late-bound region.
 #[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
 pub struct ClosureOutlivesSubjectTy<'tcx> {
     inner: Ty<'tcx>,
 }
 
+/// DO NOT implement `TypeVisitable` or `TypeFoldable` traits, because this
+/// type is not recognized as a binder for late-bound region.
+impl<'tcx, I> !ty::TypeFoldable<I> for ClosureOutlivesSubjectTy<'tcx> {}
+impl<'tcx, I> !ty::TypeVisitable<I> for ClosureOutlivesSubjectTy<'tcx> {}
+
 impl<'tcx> ClosureOutlivesSubjectTy<'tcx> {
     /// All regions of `ty` must be of kind `ReVar` and must represent
     /// universal regions *external* to the closure.