Add more test cases for PR31384

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@289778 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR31384.pass.cpp

@@ -15,24 +15,74 @@
 // template <class TupleLike> tuple(TupleLike&&); // libc++ extension
 
 // See llvm.org/PR31384
-
 #include <tuple>
 #include <cassert>
 
-
 int count = 0;
 
+struct Explicit {
+  Explicit() = default;
+  explicit Explicit(int) {}
+};
+
+struct Implicit {
+  Implicit() = default;
+  Implicit(int) {}
+};
+
 template<class T>
-struct derived : std::tuple<T> {
+struct Derived : std::tuple<T> {
   using std::tuple<T>::tuple;
   template<class U>
-  operator std::tuple<U>() && {
-    ++count;
-    return {};
-  }
+  operator std::tuple<U>() && { ++count; return {}; }
+};
+
+
+template<class T>
+struct ExplicitDerived : std::tuple<T> {
+  using std::tuple<T>::tuple;
+  template<class U>
+  explicit operator std::tuple<U>() && { ++count; return {}; }
 };
 
 int main() {
-  std::tuple<int> foo = derived<int&&>{42};
-  assert(count == 1);
+  {
+    std::tuple<Explicit> foo = Derived<int>{42};
+    assert(count == 1);
+    std::tuple<Explicit> bar(Derived<int>{42});
+    assert(count == 2);
+  }
+  count = 0;
+  {
+    std::tuple<Implicit> foo = Derived<int>{42};
+    assert(count == 1);
+    std::tuple<Implicit> bar(Derived<int>{42});
+    assert(count == 2);
+  }
+  count = 0;
+  {
+    static_assert(!std::is_convertible<
+        ExplicitDerived<int>, std::tuple<Explicit>>::value, "");
+    std::tuple<Explicit> bar(ExplicitDerived<int>{42});
+    assert(count == 1);
+  }
+  count = 0;
+  {
+    // FIXME: Libc++ incorrectly rejects this code.
+#ifndef _LIBCPP_VERSION
+    std::tuple<Implicit> foo = ExplicitDerived<int>{42};
+    static_assert(std::is_convertible<
+        ExplicitDerived<int>, std::tuple<Implicit>>::value,
+        "correct STLs accept this");
+#else
+    static_assert(!std::is_convertible<
+        ExplicitDerived<int>, std::tuple<Implicit>>::value,
+        "libc++ incorrectly rejects this");
+#endif
+    assert(count == 0);
+    std::tuple<Implicit> bar(ExplicitDerived<int>{42});
+    assert(count == 1);
+  }
+  count = 0;
+
 }