Ask compiler to use shim for rustc_nocopy_clone_marker types

Author: Manishearth

src/librustc/traits/select.rs

@@ -2126,7 +2126,20 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 }
             }
 
-            ty::TyAdt(..) | ty::TyProjection(..) | ty::TyParam(..) | ty::TyAnon(..) => {
+            ty::TyAdt(adt, substs) => {
+                let attrs = self.tcx().get_attrs(adt.did);
+                if adt.is_enum() && attrs.iter().any(|a| a.check_name("rustc_nocopy_clone_marker")) {
+                    // for Clone
+                    let mut iter = substs.types()
+                        .chain(adt.all_fields().map(|f| f.ty(self.tcx(), substs)));
+                    Where(ty::Binder(iter.collect()))
+                } else {
+                    // Fallback to whatever user-defined impls exist in this case.
+                    None                
+                }
+            }
+
+            ty::TyProjection(..) | ty::TyParam(..) | ty::TyAnon(..) => {
                 // Fallback to whatever user-defined impls exist in this case.
                 None
             }

src/libsyntax_ext/deriving/clone.rs

@@ -55,6 +55,16 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt,
                         substructure = combine_substructure(Box::new(|c, s, sub| {
                             cs_clone_shallow("Clone", c, s, sub, false)
                         }));
+                    } else if attr::contains_name(&annitem.attrs, "rustc_nocopy_clone_marker") {
+                        if let ItemKind::Enum(..) = annitem.node {
+                            // Do nothing, this will be handled in a shim
+                            return
+                        }
+                        bounds = vec![];
+                        is_shallow = false;
+                        substructure = combine_substructure(Box::new(|c, s, sub| {
+                            cs_clone("Clone", c, s, sub)
+                        }));
                     } else {
                         bounds = vec![];
                         is_shallow = false;