re PR c++/80471 ((gcc extension) Forwarding-reference `auto` function parameters…

re PR c++/80471 ((gcc extension) Forwarding-reference `auto` function parameters do not follow the same rules as template functions or generic lambdas)

2017-10-04  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/80471
	* g++.dg/cpp1y/pr80471.C: New.

From-SVN: r253432

gcc/testsuite/ChangeLog

 2017-10-04  Paolo Carlini  <paolo.carlini@oracle.com>
 
+	PR c++/80471
+	* g++.dg/cpp1y/pr80471.C: New.
+
+2017-10-04  Paolo Carlini  <paolo.carlini@oracle.com>
+
 	PR c++/78131
 	* g++.dg/cpp1z/constexpr-lambda17.C: New.
 

gcc/testsuite/g++.dg/cpp1y/pr80471.C

+// PR c++/80471
+// { dg-do compile { target c++14 } }
+// { dg-options "" }
+
+template <class, class>
+constexpr bool is_same = false;
+template <class T>
+constexpr bool is_same<T, T> = true;
+
+template<class T>
+decltype(auto) f(T&& a){return a;}
+
+decltype(auto) g(auto&& a){return a;}
+
+auto z = [](auto&& a) -> decltype(auto) { return a; };
+
+int main()
+{
+  int i;
+  static_assert(is_same< decltype(f(i)), int& >, "");
+  static_assert(is_same< decltype(g(i)), int  >, "");
+  static_assert(is_same< decltype(z(i)), int& >, "");
+}