x3/attribute_type_check.cpp:34:42: error: 'decay_t' is not a member of 'boost'; did you mean 'std::decay_t'?
   34 | static inline checked_attr_parser<boost::decay_t<Value>, Expected>
      |                                          ^~~~~~~

--- a/libs/spirit/test/x3/attribute_type_check.cpp
+++ b/libs/spirit/test/x3/attribute_type_check.cpp
@@ -31,7 +31,7 @@ struct checked_attr_parser : x3::attr_pa
 };
 
 template <typename Expected, typename Value>
-static inline checked_attr_parser<boost::decay_t<Value>, Expected>
+static inline checked_attr_parser<std::decay_t<Value>, Expected>
 checked_attr(Value&& value) { return { std::forward<Value>(value) }; }
 
 // instantiate our type checker