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+#ifndef RUBY3_CONSTANT_P_H /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY3_CONSTANT_P_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 `RUBY3` or `ruby3` 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 #RUBY3_CONSTANT_P.
+ *
+ * Note that __builtin_constant_p can be applicable inside of inline functions,
+ * according to GCC manual. Clang lacks that feature, though.
+ *
+ * @see https://bugs.llvm.org/show_bug.cgi?id=4898
+ * @see https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
+ */
+#include "ruby/3/has/builtin.h"
+
+#if RUBY3_HAS_BUILTIN(__builtin_constant_p)
+# define RUBY3_CONSTANT_P(expr) __builtin_constant_p(expr)
+#else
+# define RUBY3_CONSTANT_P(expr) 0
+#endif
+
+#endif /* RUBY3_CONSTANT_P_H */