gcc/testsuite/g++.dg/warn/Wctad-maybe-unsupported2.C

// { dg-do compile { target c++17 } }
// { dg-options "-Wctad-maybe-unsupported" }

#include "Wctad-maybe-unsupported.h"

A a{42}; // { dg-bogus "may not intend to support class template argument deduction" }