Index: clang-tools-extra/trunk/clang-tidy/misc/UnusedUsingDeclsCheck.h
===================================================================
--- clang-tools-extra/trunk/clang-tidy/misc/UnusedUsingDeclsCheck.h
+++ clang-tools-extra/trunk/clang-tidy/misc/UnusedUsingDeclsCheck.h
@@ -36,9 +36,15 @@
   struct UsingDeclContext {
     explicit UsingDeclContext(const UsingDecl *FoundUsingDecl)
         : FoundUsingDecl(FoundUsingDecl), IsUsed(false) {}
+    // A set saves all UsingShadowDecls introduced by a UsingDecl. A UsingDecl
+    // can introduce multiple UsingShadowDecls in some cases (such as
+    // overloaded functions).
     llvm::SmallPtrSet<const Decl *, 4> UsingTargetDecls;
+    // The original UsingDecl.
     const UsingDecl *FoundUsingDecl;
+    // The source range of the UsingDecl.
     CharSourceRange UsingDeclRange;
+    // Whether the UsingDecl is used.
     bool IsUsed;
   };
 
Index: clang-tools-extra/trunk/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
===================================================================
--- clang-tools-extra/trunk/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
+++ clang-tools-extra/trunk/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
@@ -41,11 +41,17 @@
   if (const auto *Using = Result.Nodes.getNodeAs<UsingDecl>("using")) {
     // Ignores using-declarations defined in macros.
     if (Using->getLocation().isMacroID())
-      return ;
+      return;
 
     // Ignores using-declarations defined in class definition.
     if (isa<CXXRecordDecl>(Using->getDeclContext()))
-      return ;
+      return;
+
+    // FIXME: We ignore using-decls defined in function definitions at the
+    // moment because of false positives caused by ADL and different function
+    // scopes.
+    if (isa<FunctionDecl>(Using->getDeclContext()))
+      return;
 
     UsingDeclContext Context(Using);
     Context.UsingDeclRange = CharSourceRange::getCharRange(
@@ -97,11 +103,14 @@
 }
 
 void UnusedUsingDeclsCheck::removeFromFoundDecls(const Decl *D) {
+  // FIXME: Currently, we don't handle the using-decls being used in different
+  // scopes (such as different namespaces, different functions). Instead of
+  // giving an incorrect message, we mark all of them as used.
+  //
+  // FIXME: Use a more efficient way to find a matching context.
   for (auto &Context : Contexts) {
-    if (Context.UsingTargetDecls.count(D->getCanonicalDecl()) > 0) {
+    if (Context.UsingTargetDecls.count(D->getCanonicalDecl()) > 0)
       Context.IsUsed = true;
-      break;
-    }
   }
 }
 
Index: clang-tools-extra/trunk/test/clang-tidy/misc-unused-using-decls.cpp
===================================================================
--- clang-tools-extra/trunk/test/clang-tidy/misc-unused-using-decls.cpp
+++ clang-tools-extra/trunk/test/clang-tidy/misc-unused-using-decls.cpp
@@ -17,6 +17,8 @@
   static int ii;
 };
 template <typename T> class J {};
+class G;
+class H;
 
 class Base {
  public:
@@ -99,6 +101,24 @@
 USING_FUNC
 #undef USING_FUNC
 
+namespace N1 {
+// n::G is used in namespace N2.
+// Currently, the check doesn't support multiple scopes. All the relevant
+// using-decls will be marked as used once we see an usage even the usage is in
+// other scope.
+using n::G;
+}
+
+namespace N2 {
+using n::G;
+void f(G g);
+}
+
+void IgnoreFunctionScope() {
+// Using-decls defined in function scope will be ignored.
+using n::H;
+}
+
 // ----- Usages -----
 void f(B b);
 void g() {
@@ -112,4 +132,3 @@
   UsedTemplateFunc<int>();
   cout << endl;
 }
-