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diff --git a/include/ruby/internal/attr/maybe_unused.h b/include/ruby/internal/attr/maybe_unused.h
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+#ifndef RBIMPL_ATTR_MAYBE_UNUSED_H /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_MAYBE_UNUSED_H
+/**
+ * @file
+ * @author Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright This file is a part of the programming language Ruby.
+ * Permission is hereby granted, to either redistribute and/or
+ * modify this file, provided that the conditions mentioned in the
+ * file COPYING are met. Consult the file for details.
+ * @warning Symbols prefixed with either `RBIMPL` or `rbimpl` are
+ * implementation details. Don't take them as canon. They could
+ * rapidly appear then vanish. The name (path) of this header file
+ * is also an implementation detail. Do not expect it to persist
+ * at the place it is now. Developers are free to move it anywhere
+ * anytime at will.
+ * @note To ruby-core: remember that this header can be possibly
+ * recursively included from extension libraries written in C++.
+ * Do not expect for instance `__VA_ARGS__` is always available.
+ * We assume C99 for ruby itself but we don't assume languages of
+ * extension libraries. They could be written in C++98.
+ * @brief Defines #RBIMPL_ATTR_MAYBE_UNUSED.
+ */
+#include "ruby/impl/has/attribute.h"
+#include "ruby/impl/has/c_attribute.h"
+#include "ruby/impl/has/cpp_attribute.h"
+
+/** Wraps (or simulates) `[[maybe_unused]]` */
+#if RBIMPL_HAS_CPP_ATTRIBUTE(maybe_unused)
+# define RBIMPL_ATTR_MAYBE_UNUSED() [[maybe_unused]]
+#elif RBIMPL_HAS_C_ATTRIBUTE(maybe_unused)
+# define RBIMPL_ATTR_MAYBE_UNUSED() [[maybe_unused]]
+#elif RBIMPL_HAS_ATTRIBUTE(unused)
+# define RBIMPL_ATTR_MAYBE_UNUSED() __attribute__((__unused__))
+#else
+# define RBIMPL_ATTR_MAYBE_UNUSED() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_MAYBE_UNUSED */