Stop generating Clone impls when there isn't a derive(Copy)

Author: Manishearth

src/libsyntax/ext/derive.rs

@@ -77,6 +77,9 @@ pub fn add_derived_markers<T>(cx: &mut ExtCtxt, span: Span, traits: &[ast::Path]
         if names.contains(&Symbol::intern("Copy")) {
             let meta = cx.meta_word(span, Symbol::intern("rustc_copy_clone_marker"));
             attrs.push(cx.attribute(span, meta));
+        } else if names.contains(&Symbol::intern("Clone")) {
+            let meta = cx.meta_word(span, Symbol::intern("rustc_nocopy_clone_marker"));
+            attrs.push(cx.attribute(span, meta));
         }
         attrs
     })

src/libsyntax/feature_gate.rs

@@ -869,7 +869,10 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                                    "rustc_attrs",
                                                    "internal implementation detail",
                                                    cfg_fn!(rustc_attrs))),
-
+    ("rustc_nocopy_clone_marker", Whitelisted, Gated(Stability::Unstable,
+                                                   "rustc_attrs",
+                                                   "internal implementation detail",
+                                                   cfg_fn!(rustc_attrs))),
     // FIXME: #14408 whitelist docs since rustdoc looks at them
     ("doc", Whitelisted, Ungated),