From e94cccc81fb16ef3fd479dc6b83d91fa8020176f Mon Sep 17 00:00:00 2001
From: Benedek Thaler <erenon2@gmail.com>
Date: Thu, 23 Jun 2022 16:23:10 +0200
Subject: [PATCH] Fix has_tag for variant custom tag

---
 include/binlog/adapt_stdvariant.hpp  | 7 +++++++
 test/integration/LoggingVariants.cpp | 8 ++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/binlog/adapt_stdvariant.hpp b/include/binlog/adapt_stdvariant.hpp
index 0987c99..8b11855 100644
--- a/include/binlog/adapt_stdvariant.hpp
+++ b/include/binlog/adapt_stdvariant.hpp
@@ -55,6 +55,13 @@ struct CustomSerializer<std::variant<T...>>
 template <typename... T>
 struct CustomTag<std::variant<T...>>
 {
+  // Make this type not-constructible, if some Tag<T> is not constructible
+  std::conditional_t<
+    detail::conjunction<detail::has_tag<T>...>::value,
+    std::true_type,
+    mserialize::detail::BuiltinTag<void>
+  > tag_guard;
+
   static constexpr auto tag_string()
   {
     return cx_strcat(
diff --git a/test/integration/LoggingVariants.cpp b/test/integration/LoggingVariants.cpp
index e25d99b..0cb8cde 100644
--- a/test/integration/LoggingVariants.cpp
+++ b/test/integration/LoggingVariants.cpp
@@ -91,3 +91,11 @@ int main()
 
   binlog::consume(std::cout);
 }
+
+struct Adapted {};
+BINLOG_ADAPT_STRUCT(Adapted)
+
+struct NotAdapted {};
+
+static_assert(mserialize::detail::has_tag<std::variant<Adapted>>::value, "");
+static_assert(!mserialize::detail::has_tag<std::variant<NotAdapted>>::value, "");