add derive macros' helper attributes to doc output

src/librustdoc/clean/inline.rs

@@ -13,7 +13,7 @@
 use std::iter::once;
 
 use syntax::ast;
-use syntax::ext::base::MacroKind;
+use syntax::ext::base::{MacroKind, SyntaxExtension};
 use syntax_pos::Span;
 
 use rustc::hir;
@@ -465,8 +465,14 @@ fn build_macro(cx: &DocContext, did: DefId, name: ast::Name) -> clean::ItemEnum
             })
         }
         LoadedMacro::ProcMacro(ext) => {
+            let helpers = match &*ext {
+                &SyntaxExtension::ProcMacroDerive(_, ref syms, ..) => { syms.clean(cx) }
+                _ => Vec::new(),
+            };
+
             clean::ProcMacroItem(clean::ProcMacro {
                 kind: ext.kind(),
+                helpers,
             })
         }
     }

src/librustdoc/clean/mod.rs

@@ -3793,6 +3793,7 @@ impl Clean<Item> for doctree::Macro {
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct ProcMacro {
     pub kind: MacroKind,
+    pub helpers: Vec<String>,
 }
 
 impl Clean<Item> for doctree::ProcMacro {
@@ -3807,6 +3808,7 @@ impl Clean<Item> for doctree::ProcMacro {
             def_id: cx.tcx.hir.local_def_id(self.id),
             inner: ProcMacroItem(ProcMacro {
                 kind: self.kind,
+                helpers: self.helpers.clean(cx),
             }),
         }
     }