Merge pull request #2991 from shyouhei/ruby.h

Split ruby.h

24 files changed, 1085 insertions, 0 deletions

diff --git a/include/ruby/3/attr/alloc_size.h b/include/ruby/3/attr/alloc_size.h
new file mode 100644
index 0000000000..1b13e6f4a5
--- /dev/null
+++ b/include/ruby/3/attr/alloc_size.h
@@ -0,0 +1,32 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_ALLOC_SIZE.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((alloc_size))` */
+#if defined(RUBY3_ATTR_ALLOC_SIZE)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(alloc_size)
+# define RUBY3_ATTR_ALLOC_SIZE(tuple) __attribute__((__alloc_size__ tuple))
+
+#else
+# define RUBY3_ATTR_ALLOC_SIZE(tuple) /* void */
+#endif
diff --git a/include/ruby/3/attr/artificial.h b/include/ruby/3/attr/artificial.h
new file mode 100644
index 0000000000..7b0acab2f6
--- /dev/null
+++ b/include/ruby/3/attr/artificial.h
@@ -0,0 +1,46 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_ARTIFICIAL.
+ *
+ * ### Q&A ###
+ *
+ * - Q: What is this attribute?  I don't get what GCC manual is talking about.
+ *
+ * - A: In  short  it  is  an  attribute to  manipulate  GDB  backtraces.   The
+ *      attribute    makes    the   best    sense    when    it   comes    with
+ *      __attribute__((always_inline)).   When a  function annotated  with this
+ *      attribute gets inlined, and when you  somehow look at a backtrace which
+ *      includes such  inlined call site,  then the backtrace shows  the caller
+ *      and  not the  callee.  This  is handy  for instance  when an  identical
+ *      function is inlined  more than once in a single  big function.  On such
+ *      case it gets  vital to know where the inlining  happened in the callee.
+ *      See also https://stackoverflow.com/a/21936099
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((artificial))` */
+#if defined(RUBY3_ATTR_ARTIFICIAL)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(artificial)
+# define RUBY3_ATTR_ARTIFICIAL() __attribute__((__artificial__))
+
+#else
+# define RUBY3_ATTR_ARTIFICIAL() /* void */
+#endif
diff --git a/include/ruby/3/attr/cold.h b/include/ruby/3/attr/cold.h
new file mode 100644
index 0000000000..6c1093d1ff
--- /dev/null
+++ b/include/ruby/3/attr/cold.h
@@ -0,0 +1,38 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_COLD.
+ */
+#include "ruby/3/compiler_is.h"
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((cold))` */
+#if defined(RUBY3_ATTR_COLD)
+# /* Take that. */
+
+#elif RUBY3_COMPILER_IS(SunPro)
+# /* Recent SunPro has __has_attribute, and is borken. */
+# /* It reports it has attribute cold, reality isn't (warnings issued). */
+# define RUBY3_ATTR_COLD() /* void */
+
+#elif RUBY3_HAS_ATTRIBUTE(cold)
+# define RUBY3_ATTR_COLD() __attribute__((__cold__))
+
+#else
+# define RUBY3_ATTR_COLD() /* void */
+#endif
diff --git a/include/ruby/3/attr/const.h b/include/ruby/3/attr/const.h
new file mode 100644
index 0000000000..06372db0c2
--- /dev/null
+++ b/include/ruby/3/attr/const.h
@@ -0,0 +1,52 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_CONST.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `__attribute__((const))` */
+#if defined(RUBY3_ATTR_CONST)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(const)
+# define RUBY3_ATTR_CONST() __attribute__((__const__))
+
+#elif RUBY3_HAS_DECLSPEC_ATTRIBUTE(noalias)
+# /* If a function can be a const, that is also a noalias. */
+# define RUBY3_ATTR_CONST() __declspec(noalias)
+
+#elif RUBY3_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RUBY3_ATTR_CONST() _Pragma("no_side_effect")
+
+#else
+# define RUBY3_ATTR_CONST() /* void */
+#endif
+
+/** Enables #RUBY3_ATTR_CONST iff. #RUBY_NDEBUG. */
+#if defined(RUBY3_ATTR_CONST_ON_NDEBUG)
+# /* Take that. */
+
+#elif RUBY_NDEBUG
+# define RUBY3_ATTR_CONST_ON_NDEBUG() RUBY3_ATTR_CONST()
+
+#else
+# define RUBY3_ATTR_CONST_ON_NDEBUG() /* void */
+#endif
diff --git a/include/ruby/3/attr/constexpr.h b/include/ruby/3/attr/constexpr.h
new file mode 100644
index 0000000000..5c09bced49
--- /dev/null
+++ b/include/ruby/3/attr/constexpr.h
@@ -0,0 +1,91 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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      #RUBY3_ATTR_CONSTEXPR.
+ */
+#include "ruby/3/has/feature.h"
+#include "ruby/3/compiler_is.h"
+#include "ruby/3/token_paste.h"
+
+/** @cond INTERNAL_MACRO*/
+#if defined(RUBY3_ATTR_CONSTEXPR)
+# /* Take that. */
+
+#elif ! defined(__cplusplus)
+# /* Makes no sense. */
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 0
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 0
+
+#elif defined(__cpp_constexpr)
+# /* https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations */
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 (__cpp_constexpr >= 200704L)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 (__cpp_constexpr >= 201304L)
+
+#elif RUBY3_COMPILER_SINCE(MSVC, 19, 0, 0)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 RUBY3_COMPILER_SINCE(MSVC, 19, 00, 00)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 RUBY3_COMPILER_SINCE(MSVC, 19, 11, 00)
+
+#elif RUBY3_COMPILER_SINCE(SunPro, 5, 13, 0)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 (__cplusplus >= 201103L)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 (__cplusplus >= 201402L)
+
+#elif RUBY3_COMPILER_SINCE(GCC, 4, 9, 0)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 (__cplusplus >= 201103L)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 (__cplusplus >= 201402L)
+
+#elif RUBY3_HAS_FEATURE(cxx_relaxed_constexpr)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 1
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 1
+
+#elif RUBY3_HAS_FEATURE(cxx_constexpr)
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 1
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 0
+
+#else
+# /* :FIXME: icpc must have constexpr but don't know how to detect. */
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX11 0
+# define RUBY3_HAS_ATTR_CONSTEXPR_CXX14 0
+#endif
+/** @endcond */
+
+/** Wraps (or simulates) C++11 `constexpr`.  */
+#if defined(RUBY3_ATTR_CONSTEXPR)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTR_CONSTEXPR_CXX14
+# define RUBY3_ATTR_CONSTEXPR(_) constexpr
+
+#elif RUBY3_HAS_ATTR_CONSTEXPR_CXX11
+# define RUBY3_ATTR_CONSTEXPR(_) RUBY3_TOKEN_PASTE(RUBY3_ATTR_CONSTEXPR_, _)
+# define RUBY3_ATTR_CONSTEXPR_CXX11 constexpr
+# define RUBY3_ATTR_CONSTEXPR_CXX14 /* void */
+
+#else
+# define RUBY3_ATTR_CONSTEXPR(_) /* void */
+#endif
+
+/** Enables #RUBY3_ATTR_CONSTEXPR iff. #RUBY_NDEBUG. */
+#if defined(RUBY3_ATTR_CONSTEXPR_ON_NDEBUG)
+# /* Take that. */
+
+#elif RUBY_NDEBUG
+# define RUBY3_ATTR_CONSTEXPR_ON_NDEBUG(_) RUBY3_ATTR_CONSTEXPR(_)
+
+#else
+# define RUBY3_ATTR_CONSTEXPR_ON_NDEBUG(_) /* void */
+#endif
diff --git a/include/ruby/3/attr/deprecated.h b/include/ruby/3/attr/deprecated.h
new file mode 100644
index 0000000000..cea124e1fe
--- /dev/null
+++ b/include/ruby/3/attr/deprecated.h
@@ -0,0 +1,58 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_DEPRECATED.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/has/c_attribute.h"
+#include "ruby/3/has/cpp_attribute.h"
+#include "ruby/3/has/declspec_attribute.h"
+#include "ruby/3/has/extension.h"
+
+/** Wraps (or simulates) `[[deprecated]]` */
+#if defined(RUBY3_ATTR_DEPRECATED)
+# /* Take that. */
+
+#elif RUBY3_HAS_EXTENSION(attribute_deprecated_with_message)
+# define RUBY3_ATTR_DEPRECATED(msg) __attribute__((__deprecated__ msg))
+
+#elif RUBY3_COMPILER_SINCE(GCC, 4, 5, 0)
+# define RUBY3_ATTR_DEPRECATED(msg) __attribute__((__deprecated__ msg))
+
+#elif RUBY3_COMPILER_SINCE(Intel, 13, 0, 0)
+# define RUBY3_ATTR_DEPRECATED(msg) __attribute__((__deprecated__ msg))
+
+#elif RUBY3_HAS_ATTRIBUTE(deprecated) /* but not with message. */
+# define RUBY3_ATTR_DEPRECATED(msg) __attribute__((__deprecated__))
+
+#elif RUBY3_COMPILER_SINCE(MSVC, 14, 0, 0)
+# define RUBY3_ATTR_DEPRECATED(msg) __declspec(deprecated msg)
+
+#elif RUBY3_HAS_DECLSPEC_ATTRIBUTE(deprecated)
+# define RUBY3_ATTR_DEPRECATED(msg) __declspec(deprecated)
+
+#elif RUBY3_HAS_CPP_ATTRIBUTE(deprecated)
+# define RUBY3_ATTR_DEPRECATED(msg) [[deprecated msg]]
+
+#elif RUBY3_HAS_C_ATTRIBUTE(deprecated)
+# define RUBY3_ATTR_DEPRECATED(msg) [[deprecated msg]]
+
+#else
+# define RUBY3_ATTR_DEPRECATED(msg) /* void */
+#endif
diff --git a/include/ruby/3/attr/diagnose_if.h b/include/ruby/3/attr/diagnose_if.h
new file mode 100644
index 0000000000..88ad81ab2c
--- /dev/null
+++ b/include/ruby/3/attr/diagnose_if.h
@@ -0,0 +1,41 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_DIAGNOSE_IF.
+ */
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/warning_push.h"
+
+/** Wraps (or simulates) `__attribute__((diagnose_if))` */
+#if defined(RUBY3_ATTR_DIAGNOSE_IF)
+# /* Take that. */
+
+#elif RUBY3_COMPILER_BEFORE(Clang, 5, 0, 0)
+# /* https://bugs.llvm.org/show_bug.cgi?id=34319 */
+# define RUBY3_ATTR_DIAGNOSE_IF(_, __, ___) /* void */
+
+#elif RUBY3_HAS_ATTRIBUTE(diagnose_if)
+# define RUBY3_ATTR_DIAGNOSE_IF(_, __, ___) \
+    RUBY3_WARNING_PUSH() \
+    RUBY3_WARNING_IGNORED(-Wgcc-compat) \
+    __attribute__((__diagnose_if__(_, __, ___))) \
+    RUBY3_WARNING_POP()
+
+#else
+# define RUBY3_ATTR_DIAGNOSE_IF(_, __, ___) /* void */
+#endif
diff --git a/include/ruby/3/attr/enum_extensibility.h b/include/ruby/3/attr/enum_extensibility.h
new file mode 100644
index 0000000000..2135736de7
--- /dev/null
+++ b/include/ruby/3/attr/enum_extensibility.h
@@ -0,0 +1,32 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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      #RUBY3_ATTR_ENUM_EXTENSIBILITY.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((enum_extensibility))` */
+#if defined(RUBY3_ATTR_ENUM_EXTENSIBILITY)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(enum_extensibility)
+# define RUBY3_ATTR_ENUM_EXTENSIBILITY(_) __attribute__((__enum_extensibility__(_)))
+
+#else
+# define RUBY3_ATTR_ENUM_EXTENSIBILITY(_) /* void */
+#endif
diff --git a/include/ruby/3/attr/error.h b/include/ruby/3/attr/error.h
new file mode 100644
index 0000000000..15d9181fe2
--- /dev/null
+++ b/include/ruby/3/attr/error.h
@@ -0,0 +1,32 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_ERROR.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((error))` */
+#if defined(RUBY3_ATTR_ERROR)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(error)
+# define RUBY3_ATTR_ERROR(msg) __attribute__((__error__ msg))
+
+#else
+# define RUBY3_ATTR_ERROR(msg) /* void */
+#endif
diff --git a/include/ruby/3/attr/flag_enum.h b/include/ruby/3/attr/flag_enum.h
new file mode 100644
index 0000000000..a026ab5de1
--- /dev/null
+++ b/include/ruby/3/attr/flag_enum.h
@@ -0,0 +1,33 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_FLAG_ENUM.
+ * @see        https://clang.llvm.org/docs/AttributeReference.html#flag_enum
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((flag_enum)` */
+#if defined(RUBY3_ATTR_FLAG_ENUM)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(flag_enum)
+# define RUBY3_ATTR_FLAG_ENUM() __attribute__((__flag_enum__))
+
+#else
+# define RUBY3_ATTR_FLAG_ENUM() /* void */
+#endif
diff --git a/include/ruby/3/attr/forceinline.h b/include/ruby/3/attr/forceinline.h
new file mode 100644
index 0000000000..47d7d58147
--- /dev/null
+++ b/include/ruby/3/attr/forceinline.h
@@ -0,0 +1,41 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_FORCEINLINE.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/attribute.h"
+
+/**
+ * Wraps (or  simulates) `__forceinline`.  MSVC complains  on declarations like
+ * `static inline __forceinline void foo()`.   It  seems  MSVC's  `inline`  and
+ * `__forceinline` are mutually exclusive.  We have to mimic that behaviour for
+ * non-MSVC compilers.
+ */
+#if defined(RUBY3_ATTR_FORCEINLINE)
+# /* Take that. */
+
+#elif RUBY3_COMPILER_SINCE(MSVC, 12, 0, 0)
+# define RUBY3_ATTR_FORCEINLINE() __forceinline
+
+#elif RUBY3_HAS_ATTRIBUTE(always_inline)
+# define RUBY3_ATTR_FORCEINLINE() __attribute__((__always_inline__)) inline
+
+#else
+# define RUBY3_ATTR_FORCEINLINE() inline
+#endif
diff --git a/include/ruby/3/attr/format.h b/include/ruby/3/attr/format.h
new file mode 100644
index 0000000000..b41094f221
--- /dev/null
+++ b/include/ruby/3/attr/format.h
@@ -0,0 +1,42 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_FORMAT.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((format))` */
+#if defined(RUBY3_ATTR_FORMAT)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(format)
+# define RUBY3_ATTR_FORMAT(x, y, z) __attribute__((__format__(x, y, z)))
+
+#else
+# define RUBY3_ATTR_FORMAT(x, y, z) /* void */
+#endif
+
+#if defined(RUBY3_PRINTF_FORMAT)
+# /* Take that. */
+
+#elif defined(__MINGW_PRINTF_FORMAT)
+# define RUBY3_PRINTF_FORMAT __MINGW_PRINTF_FORMAT
+
+#else
+# define RUBY3_PRINTF_FORMAT __printf__
+#endif
diff --git a/include/ruby/3/attr/maybe_unused.h b/include/ruby/3/attr/maybe_unused.h
new file mode 100644
index 0000000000..3463dfb77a
--- /dev/null
+++ b/include/ruby/3/attr/maybe_unused.h
@@ -0,0 +1,40 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_MAYBE_UNUSED.
+ */
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/has/c_attribute.h"
+#include "ruby/3/has/cpp_attribute.h"
+
+/** Wraps  (or simulates)  `[[maybe_unused]]` */
+#if defined(RUBY3_ATTR_MAYBE_UNUSED)
+# /* Take that. */
+
+#elif RUBY3_HAS_CPP_ATTRIBUTE(maybe_unused)
+# define RUBY3_ATTR_MAYBE_UNUSED() [[maybe_unused]]
+
+#elif RUBY3_HAS_C_ATTRIBUTE(maybe_unused)
+# define RUBY3_ATTR_MAYBE_UNUSED() [[maybe_unused]]
+
+#elif RUBY3_HAS_ATTRIBUTE(unused)
+# define RUBY3_ATTR_MAYBE_UNUSED() __attribute__((__unused__))
+
+#else
+# define RUBY3_ATTR_MAYBE_UNUSED() /* void */
+#endif
diff --git a/include/ruby/3/attr/noalias.h b/include/ruby/3/attr/noalias.h
new file mode 100644
index 0000000000..c15f1480cb
--- /dev/null
+++ b/include/ruby/3/attr/noalias.h
@@ -0,0 +1,58 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_NOALIAS.
+ *
+ * ### Q&A ###
+ *
+ * - Q: There  are   seemingly  similar  attributes   named  #RUBY3_ATTR_CONST,
+ *      #RUBY3_ATTR_PURE, and #RUBY3_ATTR_NOALIAS.  What are the difference?
+ *
+ * - A: Allowed operations are different.
+ *
+ *     - #RUBY3_ATTR_CONST ... Functions attributed by  this are not allowed to
+ *       read/write  _any_ pointers  at all  (there are  exceptional situations
+ *       when  reading a  pointer is  possible but  forget that;  they are  too
+ *       exceptional  to be  useful).  Just  remember that  everything pointer-
+ *       related are NG.
+ *
+ *     - #RUBY3_ATTR_PURE  ...   Functions  attributed  by this  can  read  any
+ *       nonvolatile pointers, but  no writes are allowed at  all.  The ability
+ *       to read _any_ nonvolatile pointers  makes it possible to mark ::VALUE-
+ *       taking functions as being pure, as long as they are read-only.
+ *
+ *     - #RUBY3_ATTR_NOALIAS ... Can both read/write, but only through pointers
+ *       passed to  the function  as parameters.  This  is a  typical situation
+ *       when you create  a C++ non-static member function  which only concerns
+ *       `this`.  No  global variables are  allowed to read/write.  So  this is
+ *       not a  super-set of being pure.   If you want to  read something, that
+ *       has  to be  passed  to the  function as  a  pointer.  ::VALUE  -taking
+ *       functions thus cannot be attributed as such.
+ */
+#include "ruby/3/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `__declspec((noalias))` */
+#if defined(RUBY3_ATTR_NOALIAS)
+# /* Take that. */
+
+#elif RUBY3_HAS_DECLSPEC_ATTRIBUTE(noalias)
+# define RUBY3_ATTR_NOALIAS() __declspec(noalias)
+
+#else
+# define RUBY3_ATTR_NOALIAS() /* void */
+#endif
diff --git a/include/ruby/3/attr/nodiscard.h b/include/ruby/3/attr/nodiscard.h
new file mode 100644
index 0000000000..00ef068422
--- /dev/null
+++ b/include/ruby/3/attr/nodiscard.h
@@ -0,0 +1,48 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_NODISCARD.
+ */
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/has/c_attribute.h"
+#include "ruby/3/has/cpp_attribute.h"
+
+/**
+ * Wraps  (or simulates)  `[[nodiscard]]`.  In  C++  (at least  since C++20)  a
+ * nodiscard attribute can  have a message why the result  shall not be ignoed.
+ * However GCC attribute and SAL annotation cannot take them.
+ */
+#if defined(RUBY3_ATTR_NODISCARD)
+# /* Take that. */
+
+#elif RUBY3_HAS_CPP_ATTRIBUTE(nodiscard)
+# define RUBY3_ATTR_NODISCARD() [[nodiscard]]
+
+#elif RUBY3_HAS_C_ATTRIBUTE(nodiscard)
+# define RUBY3_ATTR_NODISCARD() [[nodiscard]]
+
+#elif RUBY3_HAS_ATTRIBUTE(warn_unused_result)
+# define RUBY3_ATTR_NODISCARD() __attribute__((__warn_unused_result__))
+
+#elif defined(_Check_return_)
+# /* Take SAL definition. */
+# define RUBY3_ATTR_NODISCARD() _Check_return_
+
+#else
+# define RUBY3_ATTR_NODISCARD() /* void */
+#endif
diff --git a/include/ruby/3/attr/noexcept.h b/include/ruby/3/attr/noexcept.h
new file mode 100644
index 0000000000..c5db6b3e79
--- /dev/null
+++ b/include/ruby/3/attr/noexcept.h
@@ -0,0 +1,90 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_NOEXCEPT.
+ *
+ * This isn't actually an attribute in C++ but who cares...
+ *
+ * Mainly due  to aesthetic reasons,  this one is  rarely used in  the project.
+ * But can  be handy on  occasions, especially when a  function's noexcept-ness
+ * depends on its calling functions.
+ *
+ * ### Q&A ###
+ *
+ * - Q: Can a function that raises Ruby exceptions be attributed `noexcept`?
+ *
+ * - A: Yes.   `noexcept` is  about  C++ exceptions,  not  Ruby's.  They  don't
+ *      interface each other.  You can  safely attribute a function that raises
+ *      Ruby exceptions as `noexcept`.
+ *
+ * - Q: How, then, can I assert that  a function I wrote doesn't raise any Ruby
+ *      exceptions?
+ *
+ * - A: `__attribute__((__leaf__))` is for that purpose.  A function attributed
+ *      as leaf can still throw C++  exceptions, but not Ruby's.  Note however,
+ *      that it's extremely difficult -- if  not impossible -- to assert that a
+ *      function  doesn't  raise any  Ruby  exceptions  at  all.  Use  of  that
+ *      attribute is not  recommended; mere mortals can't properly  use that by
+ *      hand.
+ *
+ * - Q: Does it make sense to attribute an inline function `noexcept`?
+ *
+ * - A: I thought so before.  But no, I don't think they are useful any longer.
+ *
+ *     - When an  inline function attributed `noexcept`  actually doesn't throw
+ *       any  exceptions at  all:  these days  I don't  see  any difference  in
+ *       generated assembly  by adding/removing this attribute.   C++ compilers
+ *       get smarter and  smarter.  Today they can infer if  it actually throws
+ *       or not without any annotations by humans (correct me if I'm wrong).
+ *
+ *     - When an inline function attributed `noexcepr` actually _does_ throw an
+ *       exception:  they  have to  call  `std::terminate`  then (C++  standard
+ *       mandates  so).  This  means exception  handling routines  are actually
+ *       enforced, not  omitted.  This doesn't impact  runtime performance (The
+ *       Itanium C++ ABI has zero-cost  exception handling), but does impact on
+ *       generated binary size.  This is bad.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/feature.h"
+
+/** Wraps (or simulates) C++11 `noexcept` */
+#if defined(RUBY3_ATTR_NOEXCEPT)
+# /* Take that. */
+
+#elif ! defined(__cplusplus)
+# /* Doesn't make sense. */
+# define RUBY3_ATTR_NOEXCEPT(_) /* void */
+
+#elif RUBY3_HAS_FEATURE(cxx_noexcept)
+# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif defined(__GXX_EXPERIMENTAL_CXX0X__) && __GXX_EXPERIMENTAL_CXX0X__
+# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif defined(__INTEL_CXX11_MODE__)
+# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif RUBY3_COMPILER_SINCE(MSVC, 19, 0, 0)
+# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif __cplusplus >= 201103L
+# define RUBY3_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#else
+# define RUBY3_ATTR_NOEXCEPT(_) /* void */
+#endif
diff --git a/include/ruby/3/attr/noinline.h b/include/ruby/3/attr/noinline.h
new file mode 100644
index 0000000000..470043794a
--- /dev/null
+++ b/include/ruby/3/attr/noinline.h
@@ -0,0 +1,36 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_NOINLINE.
+ */
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `__declspec(noinline)` */
+#if defined(RUBY3_ATTR_NOINLINE)
+# /* Take that. */
+
+#elif RUBY3_HAS_DECLSPEC_ATTRIBUTE(noinline)
+# define RUBY3_ATTR_NOINLINE() __declspec(noinline)
+
+#elif RUBY3_HAS_ATTRIBUTE(noinline)
+# define RUBY3_ATTR_NOINLINE() __attribute__((__noinline__))
+
+#else
+# define RUBY3_ATTR_NOINLINE() /* void */
+#endif
diff --git a/include/ruby/3/attr/nonnull.h b/include/ruby/3/attr/nonnull.h
new file mode 100644
index 0000000000..fff90df55b
--- /dev/null
+++ b/include/ruby/3/attr/nonnull.h
@@ -0,0 +1,32 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_NONNULL.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((nonnull))` */
+#if defined(RUBY3_ATTR_NONNULL)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(nonnull)
+# define RUBY3_ATTR_NONNULL(list) __attribute__((__nonnull__ list))
+
+#else
+# define RUBY3_ATTR_NONNULL(list) /* void */
+#endif
diff --git a/include/ruby/3/attr/noreturn.h b/include/ruby/3/attr/noreturn.h
new file mode 100644
index 0000000000..c08c824947
--- /dev/null
+++ b/include/ruby/3/attr/noreturn.h
@@ -0,0 +1,51 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_NORETURN.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/has/cpp_attribute.h"
+#include "ruby/3/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `[[noreturn]]` */
+#if defined(RUBY3_ATTR_NORETURN)
+# /* Take that. */
+
+#elif RUBY3_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RUBY3_ATTR_NORETURN() _Pragma("does_not_return")
+
+#elif RUBY3_HAS_DECLSPEC_ATTRIBUTE(noreturn)
+# define RUBY3_ATTR_NORETURN() __declspec(noreturn)
+
+#elif RUBY3_HAS_ATTRIBUTE(noreturn)
+# define RUBY3_ATTR_NORETURN() __attribute__((__noreturn__))
+
+#elif RUBY3_HAS_CPP_ATTRIBUTE(noreturn)
+# define RUBY3_ATTR_NORETURN() [[noreturn]]
+
+#elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112)
+# define RUBY3_ATTR_NORETURN() _Noreturn
+
+#elif defined(_Noreturn)
+# /* glibc <sys/cdefs.h> has this macro. */
+# define RUBY3_ATTR_NORETURN() _Noreturn
+
+#else
+# define RUBY3_ATTR_NORETURN() /* void */
+#endif
diff --git a/include/ruby/3/attr/pure.h b/include/ruby/3/attr/pure.h
new file mode 100644
index 0000000000..8ae2e91fdf
--- /dev/null
+++ b/include/ruby/3/attr/pure.h
@@ -0,0 +1,48 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_PURE.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/attribute.h"
+#include "ruby/assert.h"
+
+/** Wraps (or simulates) `__attribute__((pure))` */
+#if defined(RUBY3_ATTR_PURE)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(pure)
+# define RUBY3_ATTR_PURE() __attribute__((__pure__))
+
+#elif RUBY3_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RUBY3_ATTR_PURE() _Pragma("does_not_write_global_data")
+
+#else
+# define RUBY3_ATTR_PURE() /* void */
+#endif
+
+/** Enables #RUBY3_ATTR_PURE iff. #RUBY_NDEBUG. */
+#if defined(RUBY3_ATTR_PURE_ON_NDEBUG)
+# /* Take that. */
+
+#elif RUBY_NDEBUG
+# define RUBY3_ATTR_PURE_ON_NDEBUG() RUBY3_ATTR_PURE()
+
+#else
+# define RUBY3_ATTR_PURE_ON_NDEBUG() /* void */
+#endif
diff --git a/include/ruby/3/attr/restrict.h b/include/ruby/3/attr/restrict.h
new file mode 100644
index 0000000000..cd753584dd
--- /dev/null
+++ b/include/ruby/3/attr/restrict.h
@@ -0,0 +1,44 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_RESTRICT.
+ */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/attribute.h"
+#include "ruby/3/token_paste.h"
+
+/* :FIXME:  config.h  includes conflicting  `#define  restrict`.   MSVC can  be
+ * detected  using  `RUBY3_COMPILER_SINCE()`, but  Clang  &  family cannot  use
+ * `__has_declspec_attribute()` which involves macro substitution. */
+
+/** Wraps (or simulates) `__declspec(restrict)` */
+#if defined(RUBY3_ATTR_RESTRICT)
+# /* Take that. */
+
+#elif RUBY3_COMPILER_SINCE(MSVC, 14, 0, 0)
+# define RUBY3_ATTR_RESTRICT() __declspec(RUBY3_TOKEN_PASTE(re, strict))
+
+#elif RUBY3_HAS_ATTRIBUTE(malloc)
+# define RUBY3_ATTR_RESTRICT() __attribute__((__malloc__))
+
+#elif RUBY3_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RUBY3_ATTR_RESTRICT() _Pragma("returns_new_memory")
+
+#else
+# define RUBY3_ATTR_RESTRICT() /* void */
+#endif
diff --git a/include/ruby/3/attr/returns_nonnull.h b/include/ruby/3/attr/returns_nonnull.h
new file mode 100644
index 0000000000..269df4de69
--- /dev/null
+++ b/include/ruby/3/attr/returns_nonnull.h
@@ -0,0 +1,36 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_RETURNS_NONNULL.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((returns_nonnull))` */
+#if defined(RUBY3_ATTR_RETURNS_NONNULL)
+# /* Take that. */
+
+#elif defined(_Ret_nonnull_)
+# /* Take SAL definition. */
+# define RUBY3_ATTR_RETURNS_NONNULL() _Ret_nonnull_
+
+#elif RUBY3_HAS_ATTRIBUTE(returns_nonnull)
+# define RUBY3_ATTR_RETURNS_NONNULL() __attribute__((__returns_nonnull__))
+
+#else
+# define RUBY3_ATTR_RETURNS_NONNULL() /* void */
+#endif
diff --git a/include/ruby/3/attr/warning.h b/include/ruby/3/attr/warning.h
new file mode 100644
index 0000000000..ebd86b3a07
--- /dev/null
+++ b/include/ruby/3/attr/warning.h
@@ -0,0 +1,32 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_WARNING.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((warning))` */
+#if defined(RUBY3_ATTR_WARNING)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(warning)
+# define RUBY3_ATTR_WARNING(msg) __attribute__((__warning__ msg))
+
+#else
+# define RUBY3_ATTR_WARNING(msg) /* void */
+#endif
diff --git a/include/ruby/3/attr/weakref.h b/include/ruby/3/attr/weakref.h
new file mode 100644
index 0000000000..084f8b99dc
--- /dev/null
+++ b/include/ruby/3/attr/weakref.h
@@ -0,0 +1,32 @@
+/**                                                     \noop-*-C++-*-vi:ft=cpp
+ * @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_ATTR_WEAKREF.
+ */
+#include "ruby/3/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((weakref))` */
+#if defined(RUBY3_ATTR_WEAKREF)
+# /* Take that. */
+
+#elif RUBY3_HAS_ATTRIBUTE(weakref)
+# define RUBY3_ATTR_WEAKREF(sym) __attribute__((__weakref__(# sym)))
+
+#else
+# define RUBY3_ATTR_WEAKREF(sym) /* void */
+#endif