Re: present but cannot be compiled (Was: usability of linux/ftape-header-segment.h)

[Akim Demaille]

Thanks for the bug report!

Unfortunately, the problem comes from the package itself, not from
Autoconf.  The configure.ac script needs to be updated.  Please, send
all this message (which your output attached) to the bug list (or the
authors) of the package you were trying to configure.

Below two parts of the Autoconf documentation are included: 1. the
documentation of AC_CHECK_HEADER(S), and 2. what's to be done to
upgrade configure.ac.

Thanks!

----------------------------------------------------------------------

Generic Header Checks
---------------------

   These macros are used to find system header files not covered by the
"particular" test macros.  If you need to check the contents of a header
as well as find out whether it is present, you have to write your own
test for it (*note Writing Tests::).

 - Macro: AC_CHECK_HEADER (HEADER-FILE, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
     If the system header file HEADER-FILE is compilable, execute shell
     commands ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.
     If you just want to define a symbol if the header file is
     available, consider using `AC_CHECK_HEADERS' instead.

     For compatibility issues with older versions of Autoconf, please
     read below.

 - Macro: AC_CHECK_HEADERS (HEADER-FILE..., [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
     For each given system header file HEADER-FILE in the
     whitespace-separated argument list that exists, define
     `HAVE_HEADER-FILE' (in all capitals).  If ACTION-IF-FOUND is
     given, it is additional shell code to execute when one of the
     header files is found.  You can give it a value of `break' to
     break out of the loop on the first match.  If ACTION-IF-NOT-FOUND
     is given, it is executed when one of the header files is not found.

     For compatibility issues with older versions of Autoconf, please
     read below.

   Previous versions of Autoconf merely checked whether the header was
accepted by the preprocessor.  This was changed because the old test was
inappropriate for typical uses.  Headers are typically used to compile,
not merely to preprocess, and the old behavior sometimes accepted
headers that clashed at compile-time.  If you need to check whether a
header is preprocessable, you can use `AC_PREPROC_IFELSE' (*note
Running the Preprocessor::).

   This scheme, which improves the robustness of the test, also requires
that you make sure that headers that must be included before the
HEADER-FILE be part of the INCLUDES, (*note Default Includes::).  If
looking for `bar.h', which requires that `foo.h' be included before if
it exists, we suggest the following scheme:


AC_CHECK_HEADERS([foo.h])
AC_CHECK_HEADERS([bar.h], [], [],
[#if HAVE_FOO_H
# include <foo.h>
# endif
])

----------------------------------------------------------------------

Header Present But Cannot Be Compiled
=====================================

   The most important guideline to bear in mind when checking for
features is to mimic as much as possible the intended use.
Unfortunately, old versions of `AC_CHECK_HEADER' and `AC_CHECK_HEADERS'
failed to follow this idea, and called the preprocessor, instead of the
compiler, to check for headers.  As a result, incompatibilities between
headers went unnoticed during configuration, and maintainers finally
had to deal with this issue elsewhere.

   As of Autoconf 2.56 both checks are performed, and `configure'
complains loudly if the compiler and the preprocessor do not agree.
For the time being the result used is that of the preprocessor, to give
maintainers time to adjust their `configure.ac', but in the near
future, only the compiler will be considered.

   Consider the following example:

     $ cat number.h
     typedef int number;
     $ cat pi.h
     const number pi = 3;
     $ cat configure.ac
     AC_INIT
     AC_CHECK_HEADERS(pi.h)
     $ autoconf -Wall
     $ ./configure
     checking for gcc... gcc
     checking for C compiler default output... a.out
     checking whether the C compiler works... yes
     checking whether we are cross compiling... no
     checking for suffix of executables...
     checking for suffix of object files... o
     checking whether we are using the GNU C compiler... yes
     checking whether gcc accepts -g... yes
     checking for gcc option to accept ANSI C... none needed
     checking how to run the C preprocessor... gcc -E
     checking for egrep... grep -E
     checking for ANSI C header files... yes
     checking for sys/types.h... yes
     checking for sys/stat.h... yes
     checking for stdlib.h... yes
     checking for string.h... yes
     checking for memory.h... yes
     checking for strings.h... yes
     checking for inttypes.h... yes
     checking for stdint.h... yes
     checking for unistd.h... yes
     checking pi.h usability... no
     checking pi.h presence... yes
     configure: WARNING: pi.h: present but cannot be compiled
     configure: WARNING: pi.h: check for missing prerequisite headers?
     configure: WARNING: pi.h: proceeding with the preprocessor's result
     configure: WARNING:     ## ------------------------------------ ##
     configure: WARNING:     ## Report this to address@hidden ##
     configure: WARNING:     ## ------------------------------------ ##
     checking for pi.h... yes

The proper way the handle this case is using the fourth argument (*note
Generic Headers::):

     $ cat configure.ac
     AC_INIT
     AC_CHECK_HEADERS(number.h pi.h,,,
     [[#if HAVE_NUMBER_H
     # include <number.h>
     #endif
     ]])
     $ autoconf -Wall
     $ ./configure
     checking for gcc... gcc
     checking for C compiler default output... a.out
     checking whether the C compiler works... yes
     checking whether we are cross compiling... no
     checking for suffix of executables...
     checking for suffix of object files... o
     checking whether we are using the GNU C compiler... yes
     checking whether gcc accepts -g... yes
     checking for gcc option to accept ANSI C... none needed
     checking for number.h... yes
     checking for pi.h... yes

   See *Note Particular Headers::, for a list of headers with their
prerequisite.

----------------------------------------------------------------------

Portability of Headers
----------------------

   This section tries to collect knowledge about common headers, and the
problems they cause.  By definition, this list will always require
additions.  Please help us keeping it as complete as possible.

`inttypes.h' vs. `stdint.h'
     Paul Eggert notes that: ISO C 1999 says that `inttypes.h' includes
     `stdint.h', so there's no need to include `stdint.h' separately in
     a standard environment.  Many implementations have `inttypes.h'
     but not `stdint.h' (e.g., Solaris 7), but I don't know of any
     implementation that has `stdint.h' but not `inttypes.h'.  Nor do I
     know of any free software that includes `stdint.h'; `stdint.h'
     seems to be a creation of the committee.

`net/if.h'
     On Darwin, this file requires that `sys/socket.h' be included
     beforehand.  One should run:

          AC_CHECK_HEADERS([sys/socket.h])
          AC_CHECK_HEADERS([net/if.h], [], [],
          [#include <stdio.h>
          #if STDC_HEADERS
          # include <stdlib.h>
          # include <stddef.h>
          #else
          # if HAVE_STDLIB_H
          #  include <stdlib.h>
          # endif
          #endif
          #if HAVE_SYS_SOCKET_H
          # include <sys/socket.h>
          #endif
          ])

`stdlib.h'
     On many systems (e.g., Darwin), `stdio.h' is a prerequisite.

`sys/socket.h'
     On Darwin, `stdlib.h' is a prerequisite.
Hi,
redhat 9
autoconf (GNU Autoconf) 2.57
automake (GNU automake) 1.6.3
gcc (GCC) 3.2.2 20030222 (Red Hat Linux 3.2.2-5)
kernel 2.4.20-9

My configure.in script contain:
AC_CHECK_HEADERS(linux/ftape-header-segment.h)

I get this when I run the configure script:
------------------------------------------------------------------------
checking linux/ftape-header-segment.h usability... no
checking linux/ftape-header-segment.h presence... yes
configure: WARNING: linux/ftape-header-segment.h: present but cannot
be compiled
configure: WARNING: linux/ftape-header-segment.h: check for missing
prerequisite headers?
configure: WARNING: linux/ftape-header-segment.h: proceeding with
the preprocessor's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to address@hidden ##
configure: WARNING:     ## ------------------------------------ ##
checking for linux/ftape-header-segment.h... yes
------------------------------------------------------------------------

I get this on config.log:
------------------------------------------------------------------------
configure:13139: checking linux/ftape-header-segment.h usability
configure:13152: gcc -c -D_FILE_OFFSET_BITS=64 -g -O2 -Wall  
-D_FILE_OFFSET_BITS=64    conftest.c >&5
In file included from configure:13262:
/usr/include/linux/ftape-header-segment.h:111: parse error before "__u16"
configure:13155: $? = 1
configure: failed program was:
| #line 13141 "configure"
| /* confdefs.h.  */
|
| #define PACKAGE_NAME ""
| #define PACKAGE_TARNAME ""
| #define PACKAGE_VERSION ""
| #define PACKAGE_STRING ""
| #define PACKAGE_BUGREPORT ""
| #define CONFIGURE_COMMAND "'./configure' '--prefix=/u/martinea/linux' 
'--with-configdir=/u/martinea/etc/amanda' 
'--with-gnutar-listdir=/var/gnutar-lists' 
'--with-gnutar=/usr/local/amanda/bin/tar' '--with-bsd-security' 
'--with-user=amanda' '--with-group=amandag' '--disable-shared' 
'--mandir=/u/martinea/man' '--no-create' '--no-recursion'"
| #define PACKAGE "amanda"
| #define VERSION "2.4.4"
| #define CONFIG_DIR "/u/martinea/etc/amanda"
| #define DEFAULT_SERVER "XX.iro.umontreal.ca"
| #define FORCE_USERID 1
| #define CLIENT_LOGIN "amanda"
| #define BINARY_OWNER "amanda"
| #define DEFAULT_CONFIG "DailySet1"
| #define DEFAULT_TAPE_SERVER "XX.iro.umontreal.ca"
| #define DEFAULT_TAPE_DEVICE "/dev/null"
| #define DEFAULT_RAW_TAPE_DEVICE "/dev/null"
| #define DEFAULT_CHANGER_DEVICE "/dev/null"
| #define GNUTAR_LISTED_INCREMENTAL_DIR "/var/gnutar-lists"
| #define BSD_SECURITY 1
| #define USE_AMANDAHOSTS 1
| #define SERVER_HOST_PRINCIPLE "amanda"
| #define SERVER_HOST_INSTANCE "amanda"
| #define SERVER_HOST_KEY_FILE "/.amanda"
| #define CLIENT_HOST_PRINCIPLE "rcmd"
| #define CLIENT_HOST_INSTANCE HOSTNAME_INSTANCE
| #define CLIENT_HOST_KEY_FILE KEYFILE
| #define TICKET_LIFETIME 128
| #define MAX_TAPE_BLOCK_KB (32)
| #define AMANDA_TMPDIR "/tmp/amanda"
| #define DEBUG_CODE 1
| #define AMANDA_DBGDIR "/tmp/amanda"
| #define AMANDA_DEBUG_DAYS 4
| #define SERVICE_SUFFIX ""
| #define AMANDA_SERVICE_NAME "amanda"
| #define KAMANDA_SERVICE_NAME "kamanda"
| #define bindir "/u/martinea/linux/bin"
| #define sbindir "/u/martinea/linux/sbin"
| #define libexecdir "/u/martinea/linux/libexec"
| #define mandir "/u/martinea/man"
| #define MT_FILE_FLAG "-f"
| #define GREP "/bin/grep"
| #define GNUTAR "/usr/local/amanda/bin/tar"
| #define SAMBA_CLIENT "/usr/bin/smbclient"
| #define SAMBA_VERSION 2
| #define HAVE_GZIP 1
| #define COMPRESS_PATH "/bin/gzip"
| #define COMPRESS_SUFFIX ".gz"
| #define COMPRESS_FAST_OPT "--fast"
| #define COMPRESS_BEST_OPT "--best"
| #define UNCOMPRESS_PATH "/bin/gzip"
| #define UNCOMPRESS_OPT "-dc"
| #define MAILER "/usr/bin/Mail"
| #define LPRCMD "/usr/bin/lpr"
| #define LPRFLAG "-P"
| #define DUMP "/sbin/dump"
| #define RESTORE "/sbin/restore"
| #define HAVE_DUMP_ESTIMATE "S"
| #define STDC_HEADERS 1
| #define HAVE_SYS_TYPES_H 1
| #define HAVE_SYS_STAT_H 1
| #define HAVE_STDLIB_H 1
| #define HAVE_STRING_H 1
| #define HAVE_MEMORY_H 1
| #define HAVE_STRINGS_H 1
| #define HAVE_INTTYPES_H 1
| #define HAVE_STDINT_H 1
| #define HAVE_UNISTD_H 1
| #define HAVE_DLFCN_H 1
| #define HAVE_UNSIGNED_LONG_CONSTANTS 1
| #define RETSIGTYPE void
| #define YYTEXT_POINTER 1
| #define STDC_HEADERS 1
| #define HAVE_DIRENT_H 1
| #define HAVE_SYS_WAIT_H 1
| #define HAVE_WAIT_H 1
| #define WAIT_USES_UNION 1
| #define TIME_WITH_SYS_TIME 1
| #define HAVE_ARPA_INET_H 1
| #define HAVE_DB_H 1
| #define HAVE_FCNTL_H 1
| #define HAVE_FSTAB_H 1
| #define HAVE_GRP_H 1
| #define HAVE_LIMITS_H 1
| /* end confdefs.h.  */
| #include <stdio.h>
| #if HAVE_SYS_TYPES_H
| # include <sys/types.h>
| #endif
| #if HAVE_SYS_STAT_H
| # include <sys/stat.h>
| #endif
| #if STDC_HEADERS
| # include <stdlib.h>
| # include <stddef.h>
| #else
| # if HAVE_STDLIB_H
| #  include <stdlib.h>
| # endif
| #endif
| #if HAVE_STRING_H
| # if !STDC_HEADERS && HAVE_MEMORY_H
| #  include <memory.h>
| # endif
| # include <string.h>
| #endif
| #if HAVE_STRINGS_H
| # include <strings.h>
| #endif
| #if HAVE_INTTYPES_H
| # include <inttypes.h>
| #else
| # if HAVE_STDINT_H
| #  include <stdint.h>
| # endif
| #endif
| #if HAVE_UNISTD_H
| # include <unistd.h>
| #endif
| #include <linux/ftape-header-segment.h>
configure:13171: result: no
configure:13175: checking linux/ftape-header-segment.h presence
configure:13186: gcc -E -D_FILE_OFFSET_BITS=64    conftest.c
configure:13192: $? = 0
configure:13211: result: yes
configure:13231: WARNING: linux/ftape-header-segment.h: present but cannot be 
compiled
configure:13233: WARNING: linux/ftape-header-segment.h: check for missing 
prerequisite headers?
configure:13235: WARNING: linux/ftape-header-segment.h: proceeding with the 
preprocessor's result
configure:13247: checking for linux/ftape-header-segment.h
configure:13254: result: yes
------------------------------------------------------------------------