1 files changed, 33 insertions, 0 deletions
diff --git a/compiler/rustc_macros/src/type_visitable.rs b/compiler/rustc_macros/src/type_visitable.rs
new file mode 100644
index 000000000..14e6aa6e0
--- /dev/null
+++ b/compiler/rustc_macros/src/type_visitable.rs
@@ -0,0 +1,33 @@
+use quote::quote;
+use syn::parse_quote;
+
+pub fn type_visitable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    if let syn::Data::Union(_) = s.ast().data {
+        panic!("cannot derive on union")
+    }
+
+    if !s.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
+        s.add_impl_generic(parse_quote! { 'tcx });
+    }
+
+    s.add_bounds(synstructure::AddBounds::Generics);
+    let body_visit = s.each(|bind| {
+        quote! {
+            ::rustc_middle::ty::visit::TypeVisitable::visit_with(#bind, __visitor)?;
+        }
+    });
+    s.bind_with(|_| synstructure::BindStyle::Move);
+
+    s.bound_impl(
+        quote!(::rustc_middle::ty::visit::TypeVisitable<'tcx>),
+        quote! {
+            fn visit_with<__V: ::rustc_middle::ty::visit::TypeVisitor<'tcx>>(
+                &self,
+                __visitor: &mut __V
+            ) -> ::std::ops::ControlFlow<__V::BreakTy> {
+                match *self { #body_visit }
+                ::std::ops::ControlFlow::CONTINUE
+            }
+        },
+    )
+}