add #include guard hack

According to MSVC manual (*1), cl.exe can skip including a header file
when that:

- contains #pragma once, or
- starts with #ifndef, or
- starts with #if ! defined.

GCC has a similar trick (*2), but it acts more stricter (e. g. there
must be _no tokens_ outside of #ifndef...#endif).

Sun C lacked #pragma once for a looong time.  Oracle Developer Studio
12.5 finally implemented it, but we cannot assume such recent version.

This changeset modifies header files so that each of them include
strictly one #ifndef...#endif.  I believe this is the most portable way
to trigger compiler optimizations. [Bug #16770]

*1: https://docs.microsoft.com/en-us/cpp/preprocessor/once
*2: https://gcc.gnu.org/onlinedocs/cppinternals/Guard-Macros.html

18 files changed, 118 insertions, 48 deletions

diff --git a/include/ruby/backward/2/assume.h b/include/ruby/backward/2/assume.h
index 2be231093b..095a43876d 100644
--- a/include/ruby/backward/2/assume.h
+++ b/include/ruby/backward/2/assume.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_ASSUME_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_ASSUME_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -37,3 +39,5 @@
 # define RB_LIKELY(x)   (x)
 # define RB_UNLIKELY(x) (x)
 #endif
+
+#endif /* RUBY_BACKWARD2_ASSUME_H */
diff --git a/include/ruby/backward/2/attributes.h b/include/ruby/backward/2/attributes.h
index 0735385292..043646eb4b 100644
--- a/include/ruby/backward/2/attributes.h
+++ b/include/ruby/backward/2/attributes.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_ATTRIBUTES_H                  /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_ATTRIBUTES_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -26,8 +28,6 @@
  * - A: Don't know.   Don't blame me.  Backward compatibility is  the key here.
  *      I'm just preserving what they have been.
  */
-#ifndef  RUBY_BACKWARD2_ATTRIBUTES_H
-#define  RUBY_BACKWARD2_ATTRIBUTES_H
 #include "ruby/3/config.h"
 #include "ruby/3/attr/alloc_size.h"
 #include "ruby/3/attr/cold.h"
diff --git a/include/ruby/backward/2/bool.h b/include/ruby/backward/2/bool.h
index 8c619b8215..b2cca2a206 100644
--- a/include/ruby/backward/2/bool.h
+++ b/include/ruby/backward/2/bool.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_BOOL_H                        /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_BOOL_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -31,3 +33,5 @@
 #elif ! TRUE
 # error TRUE must be true
 #endif
+
+#endif /* RUBY_BACKWARD2_BOOL_H */
diff --git a/include/ruby/backward/2/extern.h b/include/ruby/backward/2/extern.h
index e7018342ea..697c593000 100644
--- a/include/ruby/backward/2/extern.h
+++ b/include/ruby/backward/2/extern.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_EXTERN_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_EXTERN_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -24,10 +26,7 @@
  * @brief      Synonym of #RUBY_EXTERN.
  * @deprecated #EXTERN is deprecated, use #RUBY_EXTERN instead.
  */
-#ifdef EXTERN
-# /* Stop bothering then. */
-
-#elif defined __GNUC__
+#if defined __GNUC__
 # define EXTERN \
     _Pragma("message \"EXTERN is deprecated, use RUBY_EXTERN instead\""); \
     RUBY_EXTERN
@@ -43,3 +42,5 @@
 # define EXTERN <-<-"EXTERN is deprecated, use RUBY_EXTERN instead"->->
 
 #endif
+
+#endif /* RUBY_BACKWARD2_EXTERN_H */
diff --git a/include/ruby/backward/2/gcc_version_since.h b/include/ruby/backward/2/gcc_version_since.h
index 4e2abc45f9..553b982147 100644
--- a/include/ruby/backward/2/gcc_version_since.h
+++ b/include/ruby/backward/2/gcc_version_since.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_GCC_VERSION_SINCE_H           /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_GCC_VERSION_SINCE_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -31,3 +33,5 @@
     ((RUBY3_COMPILER_VERSION_MINOR == (y))      && \
      (RUBY3_COMPILER_VERSION_PATCH == (z))))))
 #endif
+
+#endif /* RUBY_BACKWARD2_GCC_VERSION_SINCE_H */
diff --git a/include/ruby/backward/2/inttypes.h b/include/ruby/backward/2/inttypes.h
index 7e9b525a52..c6419bc7b3 100644
--- a/include/ruby/backward/2/inttypes.h
+++ b/include/ruby/backward/2/inttypes.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_INTTYPES_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_INTTYPES_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -126,3 +128,5 @@
 # define PRIxSIZE PRI_SIZE_PREFIX"x"
 # define PRIXSIZE PRI_SIZE_PREFIX"X"
 #endif
+
+#endif /* RUBY_BACKWARD2_INTTYPES_H */
diff --git a/include/ruby/backward/2/limits.h b/include/ruby/backward/2/limits.h
index 28eb1596a9..f003d86057 100644
--- a/include/ruby/backward/2/limits.h
+++ b/include/ruby/backward/2/limits.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_LIMITS_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_LIMITS_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -94,3 +96,5 @@
 # define SSIZE_MAX SHRT_MAX
 # define SSIZE_MIN SHRT_MIN
 #endif
+
+#endif /* RUBY_BACKWARD2_LIMITS_H */
diff --git a/include/ruby/backward/2/long_long.h b/include/ruby/backward/2/long_long.h
index 29b930625e..2a9b9e7f40 100644
--- a/include/ruby/backward/2/long_long.h
+++ b/include/ruby/backward/2/long_long.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_LONG_LONG_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_LONG_LONG_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -25,10 +27,7 @@
  */
 #include "ruby/3/config.h"
 
-#if defined(LONG_LONG)
-# /* Take that. */
-
-#elif RUBY3_HAS_WARNING("-Wc++11-long-long")
+#if RUBY3_HAS_WARNING("-Wc++11-long-long")
 # define HAVE_TRUE_LONG_LONG 1
 # define LONG_LONG                           \
     RUBY3_WARNING_PUSH()                     \
@@ -60,3 +59,5 @@
 # error Remember to attach a detailed description of your environment.
 # error Thank you!
 #endif
+
+#endif /* RUBY3_BACKWARD2_LONG_LONG_H */
diff --git a/include/ruby/backward/2/r_cast.h b/include/ruby/backward/2/r_cast.h
index ed529c8968..15f5339227 100644
--- a/include/ruby/backward/2/r_cast.h
+++ b/include/ruby/backward/2/r_cast.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_R_CAST_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_R_CAST_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -20,8 +22,6 @@
  *
  * Nobody is actively using this macro.
  */
-#ifndef RUBY_BACKWARD2_R_CAST_H
-#define RUBY_BACKWARD2_R_CAST_H
 #define R_CAST(st)   (struct st*)
 #define RMOVED(obj)  (R_CAST(RMoved)(obj))
 #endif /* RUBY_BACKWARD2_R_CAST_H */
diff --git a/include/ruby/backward/2/rmodule.h b/include/ruby/backward/2/rmodule.h
index bb0fc047a6..6b79636ac7 100644
--- a/include/ruby/backward/2/rmodule.h
+++ b/include/ruby/backward/2/rmodule.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_RMODULE_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_RMODULE_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -22,9 +24,8 @@
  * who is implementing the internals) could have used those macros for a while.
  * Kept public as-is here to keep some theoretical backwards compatibility.
  */
-#ifndef RMODULE_IV_TBL
 #define RMODULE_IV_TBL(m) RCLASS_IV_TBL(m)
 #define RMODULE_CONST_TBL(m) RCLASS_CONST_TBL(m)
 #define RMODULE_M_TBL(m) RCLASS_M_TBL(m)
 #define RMODULE_SUPER(m) RCLASS_SUPER(m)
-#endif
+#endif /* RUBY_BACKWARD2_RMODULE_H */
diff --git a/include/ruby/backward/2/stdalign.h b/include/ruby/backward/2/stdalign.h
index 2d970edc9d..bdea030a41 100644
--- a/include/ruby/backward/2/stdalign.h
+++ b/include/ruby/backward/2/stdalign.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_STDALIGN_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_STDALIGN_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -24,3 +26,5 @@
 #undef RUBY_ALIGNOF
 #define RUBY_ALIGNAS RUBY3_ALIGNAS
 #define RUBY_ALIGNOF RUBY3_ALIGNOF
+
+#endif /* RUBY_BACKWARD2_STDALIGN_H */
diff --git a/include/ruby/backward/2/stdarg.h b/include/ruby/backward/2/stdarg.h
index 7b37bd4571..2270e66b77 100644
--- a/include/ruby/backward/2/stdarg.h
+++ b/include/ruby/backward/2/stdarg.h
@@ -1,4 +1,6 @@
-/**                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD2_STDARG_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_STDARG_H
+/**
  * @file
  * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
@@ -41,3 +43,5 @@
 #else
 #define ANYARGS
 #endif
+
+#endif /* RUBY_BACKWARD2_STDARG_H */
diff --git a/include/ruby/backward/classext.h b/include/ruby/backward/classext.h
index 9d5747316a..61d05611bc 100644
--- a/include/ruby/backward/classext.h
+++ b/include/ruby/backward/classext.h
@@ -1,12 +1,19 @@
+#ifndef RUBY_BACKWARD_CLASSEXT_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD_CLASSEXT_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.
+ */
 #if   defined __GNUC__
 #warning use of RClass internals is deprecated
 #elif defined _MSC_VER
 #pragma message("warning: use of RClass internals is deprecated")
 #endif
 
-#ifndef RUBY_BACKWARD_CLASSEXT_H
-#define RUBY_BACKWARD_CLASSEXT_H 1
-
 typedef struct rb_deprecated_classext_struct {
     VALUE super;
 } rb_deprecated_classext_t;
@@ -15,4 +22,4 @@ typedef struct rb_deprecated_classext_struct {
 #define RCLASS_EXT(c) ((rb_deprecated_classext_t *)RCLASS(c)->ptr)
 #define RCLASS_SUPER(c) (RCLASS(c)->super)
 
-#endif	/* RUBY_BACKWARD_CLASSEXT_H */
+#endif /* RUBY_BACKWARD_CLASSEXT_H */
diff --git a/include/ruby/backward/cxxanyargs.hpp b/include/ruby/backward/cxxanyargs.hpp
index 8fda5fe906..c30ab46f43 100644
--- a/include/ruby/backward/cxxanyargs.hpp
+++ b/include/ruby/backward/cxxanyargs.hpp
@@ -1,4 +1,5 @@
-///                                                     \noop-*-C++-*-vi:ft=cpp
+#ifndef RUBY_BACKWARD_CXXANYARGS_HPP                       //-*-C++-*-vi:ft=cpp
+#define RUBY_BACKWARD_CXXANYARGS_HPP
 /// @file
 /// @author     \@shyouhei
 /// @copyright  This  file  is  a  part   of  the  programming  language  Ruby.
@@ -9,8 +10,6 @@
 ///             meant to  be a backwards  compatibility shim.  Please  stick to
 ///             C++ 98 and never use newer features, like `constexpr`.
 /// @brief      Provides old prototypes for C++ programs.
-#ifndef RUBY_BACKWARD_CXXANYARGS_HPP
-#define RUBY_BACKWARD_CXXANYARGS_HPP
 #include "ruby/3/config.h"
 #include "ruby/3/intern/class.h"
 #include "ruby/3/intern/cont.h"
diff --git a/include/ruby/backward/rubyio.h b/include/ruby/backward/rubyio.h
index a6e3a7c78b..433f425988 100644
--- a/include/ruby/backward/rubyio.h
+++ b/include/ruby/backward/rubyio.h
@@ -1,6 +1,18 @@
+#ifndef RUBY_BACKWARD_RUBYIO_H                       /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD_RUBYIO_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.
+ */
 #if   defined __GNUC__
 #warning use "ruby/io.h" instead of "rubyio.h"
 #elif defined _MSC_VER
 #pragma message("warning: use \"ruby/io.h\" instead of \"rubyio.h\"")
 #endif
 #include "ruby/io.h"
+
+#endif /* RUBY_BACKWARD_RUBYIO_H */
diff --git a/include/ruby/backward/rubysig.h b/include/ruby/backward/rubysig.h
index 7a1ca35f20..b1645cdeb0 100644
--- a/include/ruby/backward/rubysig.h
+++ b/include/ruby/backward/rubysig.h
@@ -1,23 +1,20 @@
-/**********************************************************************
-
-  rubysig.h -
-
-  $Author$
-  $Date$
-  created at: Wed Aug 16 01:15:38 JST 1995
-
-  Copyright (C) 1993-2008 Yukihiro Matsumoto
-
-**********************************************************************/
-
+#ifndef RUBYSIG_H                                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBYSIG_H
+/**
+ * @file
+ * @author     $Author$
+ * @date       Wed Aug 16 01:15:38 JST 1995
+ * @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.
+ */
 #if   defined __GNUC__
 #warning rubysig.h is obsolete
 #elif defined _MSC_VER
 #pragma message("warning: rubysig.h is obsolete")
 #endif
 
-#ifndef RUBYSIG_H
-#define RUBYSIG_H
 #include "ruby/ruby.h"
 
 #define RUBY_CRITICAL(statements) do {statements;} while (0)
@@ -26,4 +23,4 @@
 #define ALLOW_INTS do {CHECK_INTS;} while (0)
 #define CHECK_INTS rb_thread_check_ints()
 
-#endif
+#endif /* RUBYSIG_H */
diff --git a/include/ruby/backward/st.h b/include/ruby/backward/st.h
index 3e36d44cf8..ad627e5e99 100644
--- a/include/ruby/backward/st.h
+++ b/include/ruby/backward/st.h
@@ -1,6 +1,18 @@
+#ifndef RUBY_BACKWARD_ST_H                           /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD_ST_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.
+ */
 #if   defined __GNUC__
 #warning use "ruby/st.h" instead of bare "st.h"
 #elif defined _MSC_VER
 #pragma message("warning: use \"ruby/st.h\" instead of bare \"st.h\"")
 #endif
 #include "ruby/st.h"
+
+#endif /* RUBY_BACKWARD_ST_H */
diff --git a/include/ruby/backward/util.h b/include/ruby/backward/util.h
index 11d32a2da8..1974fedbb5 100644
--- a/include/ruby/backward/util.h
+++ b/include/ruby/backward/util.h
@@ -1,6 +1,18 @@
+#ifndef RUBY_BACKWARD_UTIL_H                         /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD_UTIL_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.
+ */
 #if   defined __GNUC__
 #warning use "ruby/util.h" instead of bare "util.h"
 #elif defined _MSC_VER
 #pragma message("warning: use \"ruby/util.h\" instead of bare \"util.h\"")
 #endif
 #include "ruby/util.h"
+
+#endif /* RUBY_BACKWARD_UTIL_H */