include what you use.

This reverts commit 443389effc.
This reverts commit d94960f22e.

Inclusion of header files must be explicit.  Every file shall directly
include what is necessary.

https://github.com/include-what-you-use/include-what-you-use says:

> When every file includes what it uses, then it is possible to edit any
> file and remove unused headers, without fear of accidentally breaking
> the upwards dependencies of that file. It also becomes easy to
> automatically track and update dependencies in the source code.

Though we don't use iwyu itself, the principle quoted above is a good
thing that we can agree.

Now that include guards were added to every and all of the headers
inside of our project this changeset does not increase compile time, at
least on my machine.

common.mk

@@ -3878,6 +3878,7 @@ dir.$(OBJEXT): {$(VPATH)}3/variable.h
 dir.$(OBJEXT): {$(VPATH)}3/warning_push.h
 dir.$(OBJEXT): {$(VPATH)}3/xmalloc.h
 dir.$(OBJEXT): {$(VPATH)}assert.h
+dir.$(OBJEXT): {$(VPATH)}builtin.h
 dir.$(OBJEXT): {$(VPATH)}backward/2/assume.h
 dir.$(OBJEXT): {$(VPATH)}backward/2/attributes.h
 dir.$(OBJEXT): {$(VPATH)}backward/2/bool.h
@@ -3890,7 +3891,6 @@ dir.$(OBJEXT): {$(VPATH)}backward/2/r_cast.h
 dir.$(OBJEXT): {$(VPATH)}backward/2/rmodule.h
 dir.$(OBJEXT): {$(VPATH)}backward/2/stdalign.h
 dir.$(OBJEXT): {$(VPATH)}backward/2/stdarg.h
-dir.$(OBJEXT): {$(VPATH)}builtin.h
 dir.$(OBJEXT): {$(VPATH)}config.h
 dir.$(OBJEXT): {$(VPATH)}defines.h
 dir.$(OBJEXT): {$(VPATH)}dir.c
@@ -5416,10 +5416,6 @@ explicit_bzero.$(OBJEXT): {$(VPATH)}3/compiler_is/sunpro.h
 explicit_bzero.$(OBJEXT): {$(VPATH)}3/compiler_since.h
 explicit_bzero.$(OBJEXT): {$(VPATH)}3/config.h
 explicit_bzero.$(OBJEXT): {$(VPATH)}3/dllexport.h
-explicit_bzero.$(OBJEXT): {$(VPATH)}3/has/attribute.h
-explicit_bzero.$(OBJEXT): {$(VPATH)}3/has/warning.h
-explicit_bzero.$(OBJEXT): {$(VPATH)}3/token_paste.h
-explicit_bzero.$(OBJEXT): {$(VPATH)}3/warning_push.h
 explicit_bzero.$(OBJEXT): {$(VPATH)}config.h
 explicit_bzero.$(OBJEXT): {$(VPATH)}explicit_bzero.c
 explicit_bzero.$(OBJEXT): {$(VPATH)}missing.h
@@ -11782,10 +11778,6 @@ ruby-runner.$(OBJEXT): {$(VPATH)}3/compiler_is/msvc.h
 ruby-runner.$(OBJEXT): {$(VPATH)}3/compiler_is/sunpro.h
 ruby-runner.$(OBJEXT): {$(VPATH)}3/compiler_since.h
 ruby-runner.$(OBJEXT): {$(VPATH)}3/config.h
-ruby-runner.$(OBJEXT): {$(VPATH)}3/has/attribute.h
-ruby-runner.$(OBJEXT): {$(VPATH)}3/has/warning.h
-ruby-runner.$(OBJEXT): {$(VPATH)}3/token_paste.h
-ruby-runner.$(OBJEXT): {$(VPATH)}3/warning_push.h
 ruby-runner.$(OBJEXT): {$(VPATH)}config.h
 ruby-runner.$(OBJEXT): {$(VPATH)}ruby-runner.c
 ruby-runner.$(OBJEXT): {$(VPATH)}ruby-runner.h
@@ -13089,10 +13081,6 @@ strlcat.$(OBJEXT): {$(VPATH)}3/compiler_is/sunpro.h
 strlcat.$(OBJEXT): {$(VPATH)}3/compiler_since.h
 strlcat.$(OBJEXT): {$(VPATH)}3/config.h
 strlcat.$(OBJEXT): {$(VPATH)}3/dllexport.h
-strlcat.$(OBJEXT): {$(VPATH)}3/has/attribute.h
-strlcat.$(OBJEXT): {$(VPATH)}3/has/warning.h
-strlcat.$(OBJEXT): {$(VPATH)}3/token_paste.h
-strlcat.$(OBJEXT): {$(VPATH)}3/warning_push.h
 strlcat.$(OBJEXT): {$(VPATH)}config.h
 strlcat.$(OBJEXT): {$(VPATH)}missing.h
 strlcat.$(OBJEXT): {$(VPATH)}strlcat.c
@@ -13106,10 +13094,6 @@ strlcpy.$(OBJEXT): {$(VPATH)}3/compiler_is/sunpro.h
 strlcpy.$(OBJEXT): {$(VPATH)}3/compiler_since.h
 strlcpy.$(OBJEXT): {$(VPATH)}3/config.h
 strlcpy.$(OBJEXT): {$(VPATH)}3/dllexport.h
-strlcpy.$(OBJEXT): {$(VPATH)}3/has/attribute.h
-strlcpy.$(OBJEXT): {$(VPATH)}3/has/warning.h
-strlcpy.$(OBJEXT): {$(VPATH)}3/token_paste.h
-strlcpy.$(OBJEXT): {$(VPATH)}3/warning_push.h
 strlcpy.$(OBJEXT): {$(VPATH)}config.h
 strlcpy.$(OBJEXT): {$(VPATH)}missing.h
 strlcpy.$(OBJEXT): {$(VPATH)}strlcpy.c

include/ruby/3/anyargs.h

@@ -72,6 +72,7 @@
 #include "ruby/3/attr/weakref.h"
 #include "ruby/3/cast.h"
 #include "ruby/3/config.h"
+#include "ruby/3/has/attribute.h"
 #include "ruby/3/intern/class.h"
 #include "ruby/3/intern/vm.h"
 #include "ruby/3/method.h"

include/ruby/3/arithmetic/int.h

@@ -31,6 +31,7 @@
 #include "ruby/3/dllexport.h"
 #include "ruby/3/special_consts.h"
 #include "ruby/3/value.h"
+#include "ruby/3/warning_push.h"
 #include "ruby/assert.h"
 
 #define RB_INT2NUM  rb_int2num_inline

include/ruby/3/assume.h

@@ -27,6 +27,7 @@
  */
 #include "ruby/3/config.h"
 #include "ruby/3/cast.h"
+#include "ruby/3/compiler_since.h"
 #include "ruby/3/has/builtin.h"
 #include "ruby/3/warning_push.h"
 

include/ruby/3/attr/alloc_size.h

@@ -20,6 +20,7 @@
  *             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 RUBY3_HAS_ATTRIBUTE(alloc_size)

include/ruby/3/attr/artificial.h

@@ -34,6 +34,7 @@
  *      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 RUBY3_HAS_ATTRIBUTE(artificial)

include/ruby/3/attr/cold.h

@@ -21,6 +21,7 @@
  * @brief      Defines #RUBY3_ATTR_COLD.
  */
 #include "ruby/3/compiler_is.h"
+#include "ruby/3/has/attribute.h"
 
 /** Wraps (or simulates) `__attribute__((cold))` */
 #if RUBY3_COMPILER_IS(SunPro)

include/ruby/3/attr/const.h

@@ -20,6 +20,8 @@
  *             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))` */

include/ruby/3/attr/constexpr.h

@@ -22,6 +22,7 @@
  */
 #include "ruby/3/has/feature.h"
 #include "ruby/3/compiler_is.h"
+#include "ruby/3/token_paste.h"
 
 /** @cond INTERNAL_MACRO */
 #if ! defined(__cplusplus)

include/ruby/3/attr/deprecated.h

@@ -20,6 +20,8 @@
  *             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/attr/diagnose_if.h

@@ -20,6 +20,8 @@
  *             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 RUBY3_COMPILER_BEFORE(Clang, 5, 0, 0)

include/ruby/3/attr/enum_extensibility.h

@@ -20,6 +20,7 @@
  *             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 RUBY3_HAS_ATTRIBUTE(enum_extensibility)

include/ruby/3/attr/error.h

@@ -20,6 +20,7 @@
  *             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 RUBY3_HAS_ATTRIBUTE(error)

include/ruby/3/attr/flag_enum.h

@@ -21,6 +21,7 @@
  * @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 RUBY3_HAS_ATTRIBUTE(flag_enum)

include/ruby/3/attr/forceinline.h

@@ -20,6 +20,8 @@
  *             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

include/ruby/3/attr/format.h

@@ -20,6 +20,7 @@
  *             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 RUBY3_HAS_ATTRIBUTE(format)

include/ruby/3/attr/maybe_unused.h

@@ -20,6 +20,7 @@
  *             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"
 

include/ruby/3/attr/nodiscard.h

@@ -20,6 +20,7 @@
  *             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"
 

include/ruby/3/attr/noexcept.h

@@ -61,6 +61,7 @@
  *       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` */

include/ruby/3/attr/noinline.h

@@ -20,6 +20,7 @@
  *             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)` */

include/ruby/3/attr/nonnull.h

@@ -20,6 +20,7 @@
  *             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 RUBY3_HAS_ATTRIBUTE(nonnull)

include/ruby/3/attr/noreturn.h

@@ -20,6 +20,8 @@
  *             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"
 

include/ruby/3/attr/pure.h

@@ -20,6 +20,8 @@
  *             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))` */

include/ruby/3/attr/restrict.h

@@ -20,6 +20,9 @@
  *             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

include/ruby/3/attr/returns_nonnull.h

@@ -20,6 +20,7 @@
  *             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(_Ret_nonnull_)

include/ruby/3/attr/warning.h

@@ -20,6 +20,7 @@
  *             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 RUBY3_HAS_ATTRIBUTE(warning)

include/ruby/3/attr/weakref.h

@@ -20,6 +20,7 @@
  *             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 RUBY3_HAS_ATTRIBUTE(weakref)

include/ruby/3/cast.h

@@ -25,6 +25,9 @@
  * public headers.  They could be used  from C++, and C-style casts could issue
  * warnings.  Ruby internals are pure C so they should not bother.
  */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/warning.h"
+#include "ruby/3/warning_push.h"
 
 #if ! defined(__cplusplus)
 # define RUBY3_CAST(expr) (expr)

include/ruby/3/config.h

@@ -27,10 +27,6 @@
 #endif
 
 #include "ruby/3/compiler_since.h"
-#include "ruby/3/has/warning.h"
-#include "ruby/3/has/attribute.h"
-#include "ruby/3/warning_push.h"
-#include "ruby/3/token_paste.h"
 
 #if defined(__cplusplus)
 #/* __builtin_choose_expr and __builtin_types_compatible aren't available

include/ruby/3/core/rdata.h

@@ -32,6 +32,7 @@
 #include "ruby/3/core/rbasic.h"
 #include "ruby/3/dllexport.h"
 #include "ruby/3/fl_type.h"
+#include "ruby/3/token_paste.h"
 #include "ruby/3/value.h"
 #include "ruby/3/value_type.h"
 #include "ruby/defines.h"

include/ruby/3/has/attribute.h

@@ -21,6 +21,8 @@
  * @brief      Defines #RUBY3_HAS_ATTRIBUTE.
  */
 #include "ruby/3/config.h"
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/token_paste.h"
 
 /** Wraps (or simulates) `__has_attribute`. */
 #if defined(__has_attribute)

include/ruby/3/has/builtin.h

@@ -21,6 +21,8 @@
  * @brief      Defines #RUBY3_HAS_BUILTIN.
  */
 #include "ruby/3/config.h"
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/token_paste.h"
 
 /** Wraps (or simulates) `__has_builtin`. */
 #if defined(__has_builtin) && ! RUBY3_COMPILER_IS(Intel)

include/ruby/3/has/cpp_attribute.h

@@ -21,6 +21,8 @@
  * @brief      Defines #RUBY3_HAS_CPP_ATTRIBUTE.
  */
 #include "ruby/3/compiler_is.h"
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/token_paste.h"
 
 /** @cond INTERNAL_MACRO */
 #if defined(__has_cpp_attribute)

include/ruby/3/has/declspec_attribute.h

@@ -20,6 +20,8 @@
  *             extension libraries. They could be written in C++98.
  * @brief      Defines #RUBY3_HAS_DECLSPEC_ATTRIBUTE.
  */
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/token_paste.h"
 
 /** Wraps (or simulates) `__has_declspec_attribute`. */
 #if defined(__has_declspec_attribute)

include/ruby/3/static_assert.h

@@ -22,6 +22,7 @@
  */
 #include <assert.h>
 #include "ruby/3/has/extension.h"
+#include "ruby/3/compiler_since.h"
 
 /** @cond INTERNAL_MACRO */
 #if defined(__cplusplus) && defined(__cpp_static_assert)

include/ruby/3/stdalign.h

@@ -27,8 +27,10 @@
 #endif
 
 #include "ruby/3/compiler_is.h"
+#include "ruby/3/compiler_since.h"
 #include "ruby/3/has/feature.h"
 #include "ruby/3/has/extension.h"
+#include "ruby/3/has/attribute.h"
 #include "ruby/3/has/declspec_attribute.h"
 
 /**

include/ruby/3/token_paste.h

@@ -21,6 +21,9 @@
  * @brief      Defines #RUBY3_TOKEN_PASTE.
  */
 #include "ruby/3/config.h"
+#include "ruby/3/compiler_since.h"
+#include "ruby/3/has/warning.h"
+#include "ruby/3/warning_push.h"
 
 /* :TODO: add your  compiler here.  There are many compilers  that can suppress
  * warnings via pragmas, but not all of them accept such things inside of `#if`

include/ruby/3/warning_push.h

@@ -44,6 +44,7 @@
  *    ```
  */
 #include "ruby/3/compiler_is.h"
+#include "ruby/3/compiler_since.h"
 
 #if RUBY3_COMPILER_SINCE(MSVC, 12, 0, 0)
 # /* Not sure exactly when but it seems VC++ 6.0 is a version with it.*/

include/ruby/backward/2/gcc_version_since.h

@@ -20,6 +20,7 @@
  *             extension libraries. They could be written in C++98.
  * @brief      Defines old #GCC_VERSION_SINCE
  */
+#include "ruby/3/compiler_since.h"
 
 #ifndef GCC_VERSION_SINCE
 #define GCC_VERSION_SINCE(x, y, z) RUBY3_COMPILER_SINCE(GCC, (x), (y), (z))

include/ruby/backward/2/long_long.h

@@ -26,6 +26,8 @@
  * compatibility only.
  */
 #include "ruby/3/config.h"
+#include "ruby/3/has/warning.h"
+#include "ruby/3/warning_push.h"
 
 #if RUBY3_HAS_WARNING("-Wc++11-long-long")
 # define HAVE_TRUE_LONG_LONG 1