rustdoc: Fix inlining reexported custom derives

Author: weiznich

src/librustdoc/clean/inline.rs

@@ -106,13 +106,23 @@ pub fn try_inline(cx: &DocContext, def: Def, name: ast::Name, visited: &mut FxHa
             clean::ConstantItem(build_const(cx, did))
         }
         // FIXME: proc-macros don't propagate attributes or spans across crates, so they look empty
+        Def::Macro(did, MacroKind::Derive) |
         Def::Macro(did, MacroKind::Bang) => {
             let mac = build_macro(cx, did, name);
-            if let clean::MacroItem(..) = mac {
-                record_extern_fqn(cx, did, clean::TypeKind::Macro);
-                mac
-            } else {
-                return None;
+            debug!("try_inline: {:?}", mac);
+
+            match build_macro(cx, did, name) {
+                clean::MacroItem(..) => {
+                    record_extern_fqn(cx, did, clean::TypeKind::Macro);
+                    mac
+                }
+                clean::ProcMacroItem(..) => {
+                    record_extern_fqn(cx, did, clean::TypeKind::Derive);
+                    mac
+                }
+                _ => {
+                    return None;
+                }
             }
         }
         _ => return None,