Address review comments

src/librustc_resolve/lib.rs

@@ -1195,11 +1195,9 @@ pub struct Resolver<'a> {
     pub whitelisted_legacy_custom_derives: Vec<Name>,
     pub found_unresolved_macro: bool,
 
-    // List of macros that we need to warn about as being unused.
-    // The bool is true if the macro is unused, and false if its used.
-    // Setting a bool to false should be much faster than removing a single
-    // element from a FxHashSet.
-    unused_macros: FxHashMap<DefId, bool>,
+    // List of crate local macros that we need to warn about as being unused.
+    // Right now this only includes macro_rules! macros.
+    unused_macros: FxHashSet<DefId>,
 
     // Maps the `Mark` of an expansion to its containing module or block.
     invocations: FxHashMap<Mark, &'a InvocationData<'a>>,
@@ -1406,7 +1404,7 @@ pub fn new(session: &'a Session,
             potentially_unused_imports: Vec::new(),
             struct_constructors: DefIdMap(),
             found_unresolved_macro: false,
-            unused_macros: FxHashMap(),
+            unused_macros: FxHashSet(),
         }
     }
 

src/librustc_resolve/macros.rs

@@ -291,24 +291,24 @@ fn resolve_invoc(&mut self, invoc: &mut Invocation, scope: Mark, force: bool)
             },
         };
         self.macro_defs.insert(invoc.expansion_data.mark, def.def_id());
-        self.unused_macros.get_mut(&def.def_id()).map(|m| *m = false);
+        self.unused_macros.remove(&def.def_id());
         Ok(Some(self.get_macro(def)))
     }
 
     fn resolve_macro(&mut self, scope: Mark, path: &ast::Path, kind: MacroKind, force: bool)
                      -> Result<Rc<SyntaxExtension>, Determinacy> {
         self.resolve_macro_to_def(scope, path, kind, force).map(|def| {
-            self.unused_macros.get_mut(&def.def_id()).map(|m| *m = false);
+            self.unused_macros.remove(&def.def_id());
             self.get_macro(def)
         })
     }
 
     fn check_unused_macros(&self) {
-        for (did, _) in self.unused_macros.iter().filter(|&(_, b)| *b) {
+        for did in self.unused_macros.iter() {
             let id_span = match *self.macro_map[did] {
-                           SyntaxExtension::NormalTT(_, isp, _) => isp,
-                           _ => None
-                       };
+                SyntaxExtension::NormalTT(_, isp, _) => isp,
+                _ => None,
+            };
             if let Some((id, span)) = id_span {
                 let lint = lint::builtin::UNUSED_MACROS;
                 let msg = "unused macro definition".to_string();
@@ -708,7 +708,7 @@ pub fn define_macro(&mut self, item: &ast::Item, legacy_scope: &mut LegacyScope<
             let def = Def::Macro(def_id, MacroKind::Bang);
             self.macro_exports.push(Export { name: ident.name, def: def, span: item.span });
         } else {
-            self.unused_macros.insert(def_id, true);
+            self.unused_macros.insert(def_id);
         }
     }
 

src/libsyntax/ext/tt/macro_rules.rs

@@ -252,11 +252,9 @@ pub fn compile(sess: &ParseSess, features: &RefCell<Features>, def: &ast::Item)
         valid: valid,
     });
 
-    NormalTT(
-             exp,
+    NormalTT(exp,
              Some((def.id, def.span)),
-             attr::contains_name(&def.attrs, "allow_internal_unstable")
-    )
+             attr::contains_name(&def.attrs, "allow_internal_unstable"))
 }
 
 fn check_lhs_nt_follows(sess: &ParseSess,