1 files changed, 52 insertions, 0 deletions
diff --git a/compiler/rustc_macros/src/lift.rs b/compiler/rustc_macros/src/lift.rs
new file mode 100644
index 000000000..ad7ac7404
--- /dev/null
+++ b/compiler/rustc_macros/src/lift.rs
@@ -0,0 +1,52 @@
+use quote::quote;
+use syn::{self, parse_quote};
+
+pub fn lift_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    s.add_bounds(synstructure::AddBounds::Generics);
+    s.bind_with(|_| synstructure::BindStyle::Move);
+
+    let tcx: syn::Lifetime = parse_quote!('tcx);
+    let newtcx: syn::GenericParam = parse_quote!('__lifted);
+
+    let lifted = {
+        let ast = s.ast();
+        let ident = &ast.ident;
+
+        // Replace `'tcx` lifetime by the `'__lifted` lifetime
+        let (_, generics, _) = ast.generics.split_for_impl();
+        let mut generics: syn::AngleBracketedGenericArguments = syn::parse_quote! { #generics };
+        for arg in generics.args.iter_mut() {
+            match arg {
+                syn::GenericArgument::Lifetime(l) if *l == tcx => {
+                    *arg = parse_quote!('__lifted);
+                }
+                syn::GenericArgument::Type(t) => {
+                    *arg = syn::parse_quote! { #t::Lifted };
+                }
+                _ => {}
+            }
+        }
+
+        quote! { #ident #generics }
+    };
+
+    let body = s.each_variant(|vi| {
+        let bindings = &vi.bindings();
+        vi.construct(|_, index| {
+            let bi = &bindings[index];
+            quote! { __tcx.lift(#bi)?  }
+        })
+    });
+
+    s.add_impl_generic(newtcx);
+    s.bound_impl(
+        quote!(::rustc_middle::ty::Lift<'__lifted>),
+        quote! {
+            type Lifted = #lifted;
+
+            fn lift_to_tcx(self, __tcx: ::rustc_middle::ty::TyCtxt<'__lifted>) -> Option<#lifted> {
+                Some(match self { #body })
+            }
+        },
+    )
+}