gcc/testsuite/g++.dg/cpp1z/nontype-auto2.C - gcc - Git at Google

 // Testcase from P0127R2
 // { dg-do compile { target c++17 } }

 template <typename T> struct S;
 template <typename T, T n> struct S<int[n]> {
   using Q = T;
 };

 typedef S<int[42]>::Q V;
 typedef decltype(sizeof 0) V;  // OK; T was deduced to std::size_t from the type int[42]
	// Testcase from P0127R2
	// { dg-do compile { target c++17 } }

	template <typename T> struct S;
	template <typename T, T n> struct S<int[n]> {
	using Q = T;
	};

	typedef S<int[42]>::Q V;
	typedef decltype(sizeof 0) V; // OK; T was deduced to std::size_t from the type int[42]