Re: Don't #include gnulib-generated .h files from config.h

[Bruno Haible]

Paul Eggert wrote:
> > Thus, it's best to avoid such a situation. This holds not only for
> > <stdalign.h> but also for <stdbool.h>. For <assert.h> on the other hand
> > I think the trouble is limited, because <assert.h> always exists among the
> > system header files.
> 
> These days stdbool.h falls into pretty much the same category as 
> assert.h. As far as I know, every platform currently supported by Gnulib 
> that doesn't have a working bool builtin (and thus will include 
> stdbool.h) has a stdbool.h that should work well enough for all but the 
> most contrarian of uses. So I suggest leaving stdbool.h alone. That way, 
> we'll have better luck with Autoconf and AC_C_BOOL.

Indeed, the platforms lacking <stdbool.h> are:
  - HP-UX 11, IRIX 6.5 — both not among our target platforms any more,
  - Solaris 10 with cc — but here support can be added just by tweaking
    $CC. See
    <https://gitlab.com/ghwiki/gnow-how/-/wikis/Platforms/Configuration>

So, I'm reverting most of yesterday's change and putting in a #error
instead, to tell the user.

On Solaris 10, this error looks like this:
"../config.h", line 536: #error: "<stdbool.h> is not usable with this 
configuration. To make it usable, add -D_STDC_C99= to $CC."

On HP-UX and IRIX, it would look like this:
../config.h: error: "<stdbool.h> does not exist on this platform. Use gnulib 
module 'stdbool-c99' instead of gnulib module 'stdbool'."

> stdalign.h is more of a problem as it was introduced in C11 and Gnulib 
> doesn't require C11 yet, so we will need a fix along the lines of what 
> you suggested, though I wish the code duplication could be avoided.

The code duplication could be avoided by letting gnulib-tool include
lib/stdalign.in.h into the shipped copy of m4/stdalign.m4. I'm still
thinking about how to achieve this in a way that is not a special-case
hack but more useful in general.


2022-09-25  Bruno Haible  <bruno@clisp.org>

        stdbool: Mostly revert last patch.
        * m4/c-bool.m4 (gl_C_BOOL): If stdbool.h does not exist, just err out.
        * modules/stdbool (Files): Remove m4/stdbool.m4.

diff --git a/ChangeLog b/ChangeLog
index 1c54eabb49..24553445f6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,9 +1,16 @@
+2022-09-25  Bruno Haible  <bruno@clisp.org>
+
+       stdbool: Mostly revert last patch.
+       * m4/c-bool.m4 (gl_C_BOOL): If stdbool.h does not exist, just err out.
+       * modules/stdbool (Files): Remove m4/stdbool.m4.
+
 2022-09-24  Bruno Haible  <bruno@clisp.org>
 
        stdbool: Don't #include a gnulib-generated stdbool.h from config.h.
        * m4/c-bool.m4 (gl_C_BOOL): Check for stdbool.h and for _Bool. If
        stdbool.h does not exist, don't #include <stdbool.h> but instead put the
        substitute code into config.h.
+       * modules/stdbool (Files): Add m4/stdbool.m4.
 
 2022-09-24  Bruno Haible  <bruno@clisp.org>
 
diff --git a/m4/c-bool.m4 b/m4/c-bool.m4
index 129981d2f7..bb109b7796 100644
--- a/m4/c-bool.m4
+++ b/m4/c-bool.m4
@@ -23,8 +23,6 @@ AC_DEFUN([gl_C_BOOL],
   fi
 
   AC_CHECK_HEADERS_ONCE([stdbool.h])
-  AC_REQUIRE([AC_CHECK_HEADER_STDBOOL])
-  AC_DEFINE_UNQUOTED([HAVE__BOOL],[$HAVE__BOOL])
 
   dnl The "zz" puts this toward config.h's end, to avoid potential
   dnl collisions with other definitions.
@@ -39,39 +37,11 @@ AC_DEFUN([gl_C_BOOL],
 #  if HAVE_STDBOOL_H
 #   include <stdbool.h>
 #  else
-    /* Substitute.  Keep consistent with gnulib/lib/stdbool.in.h.  */
-#   ifndef _GL_STDBOOL_H
-#    define _GL_STDBOOL_H
-#    ifdef __cplusplus
-#     if !defined _MSC_VER
-#      define _Bool bool
-#      define bool bool
-#     endif
-#    else
-#     if !defined __GNUC__
-#      define _Bool signed char
-#     else
-#      if !HAVE__BOOL
-typedef enum { _Bool_must_promote_to_int = -1, false = 0, true = 1 } _Bool;
-#      endif
-#     endif
-#     define bool _Bool
-#    endif
-#    ifdef __cplusplus
-#     if !defined _MSC_VER
-#      define false false
-#      define true true
-#     endif
-#     if defined __SUNPRO_CC && true != 1
-#      undef true
-#      define true (!false)
-#     endif
-#    else
-#     define false 0
-#     define true 1
-#    endif
-#    define __bool_true_false_are_defined 1
-#   endif /* _GL_STDBOOL_H */
+#   if defined __SUNPRO_C
+#    error "<stdbool.h> is not usable with this configuration. To make it 
usable, add -D_STDC_C99= to $CC."
+#   else
+#    error "<stdbool.h> does not exist on this platform. Use gnulib module 
'stdbool-c99' instead of gnulib module 'stdbool'."
+#   endif
 #  endif
 # endif
 # if !true
diff --git a/modules/stdbool b/modules/stdbool
index 664df5e0f8..2e771a2336 100644
--- a/modules/stdbool
+++ b/modules/stdbool
@@ -3,7 +3,6 @@ A bool that is like C23.
 
 Files:
 m4/c-bool.m4
-m4/stdbool.m4
 
 Depends-on:
 c99