Fix PR30274

[arphaman]

Summary

This fixes PR 30274 by making sure that we skip the 'Using' and 'ConstructorUsingShadowDecl' declarations when evaluating the '__has_nothrow_constructor' trait for a C++ type.

[arphaman]

(Forgot to mention) This is a a fix for the regression introduced by r274049.

[arphaman]

I just noticed that PR 30274 is actually a duplicate of PR 29087, which already has a patch with a fix in review. This patch is now abandoned. Sorry about not noticing the duplicate earlier.

lib/Sema/SemaExprCXX.cpp

       bool FoundConstructor = false;
       for (const auto *ND : Self.LookupConstructors(RD)) {
         // FIXME: In C++0x, a constructor template can be a default constructor.
-        if (isa<FunctionTemplateDecl>(ND))
+        // Skip the inherited constructors as we are only interested in default
+        // constructors which can't be inherited.
+        if (isa<FunctionTemplateDecl>(ND) || isa<UsingDecl>(ND) ||
+            isa<ConstructorUsingShadowDecl>(ND))
           continue;
         const CXXConstructorDecl *Constructor = cast<CXXConstructorDecl>(ND);
         if (Constructor->isDefaultConstructor()) {

test/SemaCXX/PR30274-inherited-constructor-has-nothrow.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
+// expected-no-diagnostics
+
+struct Base {
+    Base(int a) : i(a) {}
+    int i;
+};
+
+struct Derived : Base {
+    using Base::Base;
+};
+
+int foo() {
+   return __has_nothrow_constructor(Derived);
+}