Fix a wrong check in misc-unused-using-decls

[hokein]

Summary

We should check whether a UsingDecl is defined in macros or in class
definition, not TargetDecls of the UsingDecl.

[alexfh]

LG

clang-tidy/misc/UnusedUsingDeclsCheck.cpp

 #include "clang/Lex/Lexer.h"
 
 using namespace clang::ast_matchers;
 
 namespace clang {
 namespace tidy {
 namespace misc {
 
-// A function that helps to tell whether a TargetDecl will be checked.
-// We only check a TargetDecl if :
-//   * The corresponding UsingDecl is not defined in macros or in class
-//     definitions.
-//   * Only variable, function and class types are considered.
+// A function that helps to tell whether a TargetDecl in a UsingDecl will be
+// checked. Only variable, function, function template, class template and class
+// are considered.
 static bool ShouldCheckDecl(const Decl *TargetDecl) {
-  // Ignores using-declarations defined in macros.
-  if (TargetDecl->getLocation().isMacroID())
-    return false;
-
-  // Ignores using-declarations defined in class definition.
-  if (isa<CXXRecordDecl>(TargetDecl->getDeclContext()))
-    return false;
-
   return isa<RecordDecl>(TargetDecl) || isa<ClassTemplateDecl>(TargetDecl) ||
          isa<FunctionDecl>(TargetDecl) || isa<VarDecl>(TargetDecl) ||
          isa<FunctionTemplateDecl>(TargetDecl);
 }
 
 void UnusedUsingDeclsCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(usingDecl(isExpansionInMainFile()).bind("using"), this);
   auto DeclMatcher = hasDeclaration(namedDecl().bind("used"));
   Finder->addMatcher(loc(recordType(DeclMatcher)), this);
   Finder->addMatcher(loc(templateSpecializationType(DeclMatcher)), this);
   Finder->addMatcher(declRefExpr().bind("used"), this);
   Finder->addMatcher(callExpr(callee(unresolvedLookupExpr().bind("used"))),
                      this);
 }
 
 void UnusedUsingDeclsCheck::check(const MatchFinder::MatchResult &Result) {
   if (const auto *Using = Result.Nodes.getNodeAs<UsingDecl>("using")) {
+    // Ignores using-declarations defined in macros.
+    if (Using->getLocation().isMacroID())
+      return ;
+
+    // Ignores using-declarations defined in class definition.
+    if (isa<CXXRecordDecl>(Using->getDeclContext()))
+      return ;
+
     UsingDeclContext Context(Using);
     Context.UsingDeclRange = CharSourceRange::getCharRange(
         Using->getLocStart(),
         Lexer::findLocationAfterToken(
             Using->getLocEnd(), tok::semi, *Result.SourceManager,
             Result.Context->getLangOpts(),
             /*SkipTrailingWhitespaceAndNewLine=*/true));
     for (const auto *UsingShadow : Using->shadows()) {

test/clang-tidy/misc-unused-using-decls.cpp

 
 int UsedFunc() { return 1; }
 int UnusedFunc() { return 1; }
 template <typename T> int UsedTemplateFunc() { return 1; }
 template <typename T> int UnusedTemplateFunc() { return 1; }
 template <typename T> int UsedInTemplateFunc() { return 1; }
 void OverloadFunc(int);
 void OverloadFunc(double);
+int FuncUsedByUsingDeclInMacro() { return 1; }
 
 class ostream {
 public:
   ostream &operator<<(ostream &(*PF)(ostream &));
 };
 extern ostream cout;
 ostream &endl(ostream &os);
 }

 #define DEFINE_INT(name)        \
   namespace INT {               \
   static const int _##name = 1; \
   }                             \
   using INT::_##name
 DEFINE_INT(test);
 #undef DEFIND_INT
 
+#define USING_FUNC \
+  using n::FuncUsedByUsingDeclInMacro;
+USING_FUNC
+#undef USING_FUNC
+
 // ----- Usages -----
 void f(B b);
 void g() {
   vector<C> data;
   D::i = 1;
   F<int> f;
   void (*func)() = &G::func;
   int *i = &H::i;
   UsedInstance.i;
   UsedFunc();
   UsedTemplateFunc<int>();
   cout << endl;
 }