Re: lib/dirent.in.h fails on AIX

[Eric Blake]

Bruno Haible <bruno <at> clisp.org> writes:

> > I have no idea why:
> >   #include <math.h>
> > behaves differently than:
> >   #include "///usr/vac/include/math.h"
> > You'd figure with the #include_next <math.h> in /usr/vac/include/math.h
> > the behavior would be the same. However, the #include_next <math.h> in
> > /usr/vac/include/math.h is turned into a no-op.
> 
> Thanks for this problem summary. Since #include <math.h> works, it's not
> a problem with the inclusion guards (the "#ifdef _H_MATH" or similar), but
> - as you say - a problem with #include_next itself.
> 
> What's the result of
>   $ grep include_next /usr/vac/include/*.h /usr/vac/include/*/*.h
> ?
> 
> Probably the only solution is to use #include_next only in gnulib's math.in.h
> but not in the other header files that are overridden by gnulib. I'm applying
> this; please let us know whether it works.
> 
> Bruno
> 
> 2008-11-20  Bruno Haible  <bruno <at> clisp.org>
> 
>       Attempt to work around an AIX 5.3, 6.1 compiler bug with include_next.
>       * lib/math.in.h: Use INCLUDE_NEXT_AS_FIRST_DIRECTIVE instead of
>       INCLUDE_NEXT.

I think I see a logic bug in this patch which explains why Jens Rehsack still 
saw a failure in m4 1.4.13:

> +++ lib/math.in.h     2008-11-20 23:26:08.000000000 +0100
> @@ -22,7 +22,7 @@
>  #endif
> 
>  /* The include_next requires a split double-inclusion guard.  */
> address@hidden@ @NEXT_MATH_H@
> address@hidden@ @NEXT_MATH_H@

NEXT_MATH_H is still of the form "///usr/vac/include/math.h" here, but that's 
exactly what we said was the second of two bugs in xlc's include_next 
implementation - #include_next "absolute" is a no-op.  Let's examine the three 
classes of compilers:

>    if test $gl_cv_have_include_next = yes; then
>      INCLUDE_NEXT=include_next
> +    INCLUDE_NEXT_AS_FIRST_DIRECTIVE=include_next
>      if test -n "$GCC"; then
>        PRAGMA_SYSTEM_HEADER='#pragma GCC system_header'
>      fi

For this compiler type (including gcc), #include_next always works, NEXT_MATH_H 
is always <math.h>, and we are okay.

>    else
> -    INCLUDE_NEXT=include
> +    if test $gl_cv_have_include_next = buggy; then
> +      INCLUDE_NEXT=include
> +      INCLUDE_NEXT_AS_FIRST_DIRECTIVE=include_next

For this compiler (AIX's xlc), we want

@INCLUDE_NEXT_AS_FIRST_DIRECTIVE@ <math.h>

But we must also ensure that, for other headers,

@INCLUDE_NEXT@ @NEXT_header@

we are using the absolute path in @NEXT_header@ since @INCLUDE_NEXT@ is only 
include.

> +    else
> +      INCLUDE_NEXT=include
> +      INCLUDE_NEXT_AS_FIRST_DIRECTIVE=include

And for this type of compiler, we always want NEXT_MATH_H to 
be "///usr/vac/include/math.h", and

@INCLUDE_NEXT_AS_FIRST_DIRECTIVE@ <math.h>

would be a bug.


So, the problem is basically that NEXT_MATH_H is usable with @INCLUDE_NEXT@ 
regardless of whether it expands to include or include_next, but it is NOT 
usable with @INCLUDE_NEXT_AS_FIRST_DIRECTIVE@ in the case of xlc.  On the 
converse side, @INCLUDE_NEXT_AS_FIRST_DIRECTIVE@ <math.h> would work for gcc 
and xlc, but will break for compilers that lack include_next altogether.  The 
solution - add another substituted variable.

By the way, m4_quote(m4_defn([foo])) is overkill - m4_defn already properly 
quotes its output as a single m4 argument, so the m4_quote is a no-op (m4_quote 
is only useful when collecting multiple unquoted m4 arguments into a single 
string).


What do you think of this patch?

From: Eric Blake <address@hidden>
Date: Wed, 20 May 2009 14:45:07 -0600
Subject: [PATCH] Another try at making math.h work for AIX xlc.

* m4/include_next.m4: Avoid redundant m4_quote.
(gl_CHECK_NEXT_HEADERS): Also define
NEXT_header_AS_FIRST_DIRECTIVE.
* lib/math.in.h (includes): Use it.
Reported by Jens Rehsack.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog          |    9 +++++++++
 lib/math.in.h      |    2 +-
 m4/include_next.m4 |   31 ++++++++++++++++++++-----------
 3 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index eeab720..2f9ff72 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2009-05-20  Eric Blake  <address@hidden>
+
+       Another try at making math.h work for AIX xlc.
+       * m4/include_next.m4: Avoid redundant m4_quote.
+       (gl_CHECK_NEXT_HEADERS): Also define
+       NEXT_header_AS_FIRST_DIRECTIVE.
+       * lib/math.in.h (includes): Use it.
+       Reported by Jens Rehsack.
+
 2009-05-20  Bruno Haible  <address@hidden>

        Make zeroptr.h work on mingw.
diff --git a/lib/math.in.h b/lib/math.in.h
index a0efefd..22f47c6 100644
--- a/lib/math.in.h
+++ b/lib/math.in.h
@@ -22,7 +22,7 @@
 #endif

 /* The include_next requires a split double-inclusion guard.  */
address@hidden@ @NEXT_MATH_H@
address@hidden@ @NEXT_MATH_H_AS_FIRST_DIRECTIVE@

 #ifndef _GL_MATH_H
 #define _GL_MATH_H
diff --git a/m4/include_next.m4 b/m4/include_next.m4
index d6101fe..20b8ca1 100644
--- a/m4/include_next.m4
+++ b/m4/include_next.m4
@@ -1,4 +1,4 @@
-# include_next.m4 serial 12
+# include_next.m4 serial 13
 dnl Copyright (C) 2006-2009 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -71,9 +71,9 @@ EOF
      AC_COMPILE_IFELSE([#include <conftest.h>],
        [gl_cv_have_include_next=yes],
        [CPPFLAGS="$gl_save_CPPFLAGS -Iconftestd1a -Iconftestd2"
-        AC_COMPILE_IFELSE([#include <conftest.h>],
-          [gl_cv_have_include_next=buggy],
-          [gl_cv_have_include_next=no])
+       AC_COMPILE_IFELSE([[#include <conftest.h>]],
+         [gl_cv_have_include_next=buggy],
+         [gl_cv_have_include_next=no])
        ])
      CPPFLAGS="$gl_save_CPPFLAGS"
      rm -rf conftestd1a conftestd1b conftestd2
@@ -123,15 +123,15 @@ AC_DEFUN([gl_CHECK_NEXT_HEADERS],

   m4_foreach_w([gl_HEADER_NAME], [$1],
     [AS_VAR_PUSHDEF([gl_next_header],
-                   [gl_cv_next_]m4_quote(m4_defn([gl_HEADER_NAME])))
+                   [gl_cv_next_]m4_defn([gl_HEADER_NAME]))
      if test $gl_cv_have_include_next = yes; then
        AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
      else
        AC_CACHE_CHECK(
-        [absolute name of <]m4_quote(m4_defn([gl_HEADER_NAME]))[>],
-        m4_quote(m4_defn([gl_next_header])),
+        [absolute name of <]m4_defn([gl_HEADER_NAME])[>],
+        m4_defn([gl_next_header]),
         [AS_VAR_PUSHDEF([gl_header_exists],
-                        [ac_cv_header_]m4_quote(m4_defn([gl_HEADER_NAME])))
+                        [ac_cv_header_]m4_defn([gl_HEADER_NAME]))
          if test AS_VAR_GET(gl_header_exists) = yes; then
            AC_LANG_CONFTEST(
              [AC_LANG_SOURCE(
@@ -153,8 +153,8 @@ AC_DEFUN([gl_CHECK_NEXT_HEADERS],
            dnl so use subshell.
            AS_VAR_SET([gl_next_header],
              ['"'`(eval "$gl_absname_cpp conftest.$ac_ext") 
2>&AS_MESSAGE_LOG_FD |
-              sed -n '\#/]m4_quote(m4_defn([gl_HEADER_NAME]))[#{
-                s#.*"\(.*/]m4_quote(m4_defn([gl_HEADER_NAME]))[\)".*#\1#
+              sed -n '\#/]m4_defn([gl_HEADER_NAME])[#{
+                s#.*"\(.*/]m4_defn([gl_HEADER_NAME])[\)".*#\1#
                 s#^/[^/]#//&#
                 p
                 q
@@ -165,7 +165,16 @@ AC_DEFUN([gl_CHECK_NEXT_HEADERS],
          AS_VAR_POPDEF([gl_header_exists])])
      fi
      AC_SUBST(
-       AS_TR_CPP([NEXT_]m4_quote(m4_defn([gl_HEADER_NAME]))),
+       AS_TR_CPP([NEXT_]m4_defn([gl_HEADER_NAME])),
        [AS_VAR_GET([gl_next_header])])
+     if test $gl_cv_have_include_next == no; then
+       AC_SUBST(
+        AS_TR_CPP([NEXT_]m4_defn([gl_HEADER_NAME])[_AS_FIRST_DIRECTIVE]),
+        [AS_VAR_GET([gl_next_header])])
+     else
+       AC_SUBST(
+        AS_TR_CPP([NEXT_]m4_defn([gl_HEADER_NAME])[_AS_FIRST_DIRECTIVE]),
+        ['<'gl_HEADER_NAME'>'])
+     fi
      AS_VAR_POPDEF([gl_next_header])])
 ])
-- 
1.6.2.4