Add a missing SFINAE condition to the variant's converting constructor.

Remarks: This function shall not participate in overload resolution unless
         `is_same_v<decay_t<T>, variant>` is false, unless `decay_t<T>` is
         neither a specialization of `in_place_type_t` nor a specialization of
         `in_place_index_t`, unless `is_constructible_v<Tj, T>` is true, and
         unless the expression `FUN(std::forward<T>(t))` (with `FUN` being the
         above-mentioned set of imaginary functions) is well formed.

Depends on D34111.

Reviewers: EricWF, K-ballo

Reviewed By: EricWF

Subscribers: fhahn

Differential Revision: https://reviews.llvm.org/D34112

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@305668 91177308-0d34-0410-b5e6-96231b3b80d8

include/variant

@@ -1116,6 +1116,8 @@ public:
   template <
       class _Arg,
       enable_if_t<!is_same_v<decay_t<_Arg>, variant>, int> = 0,
+      enable_if_t<!__is_inplace_type<decay_t<_Arg>>::value, int> = 0,
+      enable_if_t<!__is_inplace_index<decay_t<_Arg>>::value, int> = 0,
       class _Tp = __variant_detail::__best_match_t<_Arg, _Types...>,
       size_t _Ip =
           __find_detail::__find_unambiguous_index_sfinae<_Tp, _Types...>::value,

test/std/utilities/variant/variant.variant/variant.ctor/T.pass.cpp

@@ -37,6 +37,9 @@ struct NoThrowT {
   NoThrowT(int) noexcept(true) {}
 };
 
+struct AnyConstructible { template <typename T> AnyConstructible(T&&) {} };
+struct NoConstructible { NoConstructible() = delete; };
+
 void test_T_ctor_noexcept() {
   {
     using V = std::variant<Dummy, NoThrowT>;
@@ -62,6 +65,17 @@ void test_T_ctor_sfinae() {
     static_assert(!std::is_constructible<V, int>::value,
                   "no matching constructor");
   }
+  {
+    using V = std::variant<AnyConstructible, NoConstructible>;
+    static_assert(
+        !std::is_constructible<V, std::in_place_type_t<NoConstructible>>::value,
+        "no matching constructor");
+    static_assert(!std::is_constructible<V, std::in_place_index_t<1>>::value,
+                  "no matching constructor");
+  }
+
+
+
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
     using V = std::variant<int, int &&>;