Sync from upstream.

test/Jamfile

@@ -137,3 +137,5 @@ run variant_json_value_from.cpp : : : $(JSON) ;
 run variant_json_value_to.cpp : : : $(JSON) ;
 
 compile variant_uses_double_storage.cpp ;
+
+run variant_derived_construct2.cpp ;

test/variant_derived_construct2.cpp

@@ -0,0 +1,60 @@
+// Copyright 2024 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+struct expr: boost::variant2::variant<bool, int, double>
+{
+    using variant::variant;
+};
+
+int main()
+{
+    using boost::variant2::get;
+
+    {
+        expr v{ true };
+
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v), true );
+    }
+
+    {
+        expr v{ 2 };
+
+        BOOST_TEST_EQ( v.index(), 1 );
+        BOOST_TEST_EQ( get<1>(v), 2 );
+    }
+
+    {
+        expr v{ 3.0 };
+
+        BOOST_TEST_EQ( v.index(), 2 );
+        BOOST_TEST_EQ( get<2>(v), 3.0 );
+    }
+
+    {
+        expr v( true );
+
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v), true );
+    }
+
+    {
+        expr v( 2 );
+
+        BOOST_TEST_EQ( v.index(), 1 );
+        BOOST_TEST_EQ( get<1>(v), 2 );
+    }
+
+    {
+        expr v( 3.0 );
+
+        BOOST_TEST_EQ( v.index(), 2 );
+        BOOST_TEST_EQ( get<2>(v), 3.0 );
+    }
+
+    return boost::report_errors();
+}