Re: present but cannot be compiled (Was: Received this bug while compiling proftpd 1.2.8rc2)

[Akim Demaille]

Thanks for the bug report!

Contrary to the message reported by ./configure, this is not a bug in
Autoconf, but the result of a recent incompatible change in Autoconf
that is likely to require the package's configure.ac to be updated.
Please, first make sure you are trying the most recent version of that
package, then, if you are, send all this message (including your
output attached) to the bug list (or the authors) of the package you
were trying to configure.

I've appended two relevant parts of the Autoconf documentation: 1. the
documentation of AC_CHECK_HEADER(S), and 2. how configure.ac should be
upgraded.

If you have some knowledge in C compilation, then there is something
more you can do to help: find out what are the prerequisite headers on
your system.

For instance, if the error message is:

       sys/socket.h: present but cannot be compiled
       sys/socket.h: check for missing prerequisite headers?
       sys/socket.h: proceeding with the preprocessor's result

then try to compile the program sample.c:

       #include <sys/socket.h>

with `cc -c sample.c'.  It will fail.  Then try to understand what
other headers are needed.  For instance, on Darwin, one needs:

       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/socket.h>

to get a successful compilation.  Then, send this additional
information to the package maintainers, together with a description of
your machine.

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.

`linux/irda.h'
     It requires `linux/types.h' and `sys/socket.h'.

`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
          ])

`stdint.h'
     See above, item `inttypes.h' vs. `stdint.h'.

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

`sys/socket.h'
     On Darwin, `stdlib.h' is a prerequisite.

`sys/ucred.h'
     On HP Tru64 5.1, `sys/types.h' is a prerequisite.

`X11/extensions/scrnsaver.h'
     Using XFree86, this header requires `X11/Xlib.h', which is probably
     so required that you might not even consider looking for it.

          AC_CHECK_HEADERS([X11/extensions/scrnsaver.h], [], [],
          [[#include <X11/Xlib.h>
          ]])

----------------------------------------------------------------------
I am running FreeBSD 5.0-RELEASE-p7. 

%./configure
checking build system type... i386-unknown-freebsd5.0
checking host system type... i386-unknown-freebsd5.0
checking target system type... i386-unknown-freebsd5.0
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 whether make sets $(MAKE)... yes
checking for a BSD-compatible install... /usr/bin/install -c
checking for ranlib... ranlib
checking for special C compiler options needed for large files... no
checking for _FILE_OFFSET_BITS value needed for large files... no
checking for _LARGE_FILES value needed for large files... no
checking whether the C compiler accepts -Wall... yes
checking for standalone crypt... no
checking for crypt in -lcrypt... yes
checking for standalone gethostbyname... yes
checking for standalone inet_aton... yes
checking for standalone nsl functions... yes
checking for standalone socket functions... yes
checking for _pw_stayopen variable... no
checking for set_auth_parameters in -lsecurity... no
checking for setprpwent in -lsec... no
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 sys/security.h usability... no
checking sys/security.h presence... no
checking for sys/security.h... no
checking krb.h usability... yes
checking krb.h presence... yes
checking for krb.h... yes
checking prot.h usability... yes
checking prot.h presence... yes
checking for prot.h... yes
checking for set_auth_parameters... no
checking for getprpwent... no
checking hpsecurity.h usability... no
checking hpsecurity.h presence... no
checking for hpsecurity.h... no
checking for hpsecurity.h workaround... no
checking for dirent.h that defines DIR... yes
checking for library containing opendir... none required
checking for ANSI C header files... (cached) yes
checking for sys/wait.h that is POSIX.1 compatible... yes
checking fcntl.h usability... yes
checking fcntl.h presence... yes
checking for fcntl.h... yes
checking sys/ioctl.h usability... yes
checking sys/ioctl.h presence... yes
checking for sys/ioctl.h... yes
checking sys/time.h usability... yes
checking sys/time.h presence... yes
checking for sys/time.h... yes
checking for unistd.h... (cached) yes
checking for memory.h... (cached) yes
checking shadow.h usability... no
checking shadow.h presence... no
checking for shadow.h... no
checking security/pam_appl.h usability... yes
checking security/pam_appl.h presence... yes
checking for security/pam_appl.h... yes
checking pam/pam_appl.h usability... no
checking pam/pam_appl.h presence... no
checking for pam/pam_appl.h... no
checking for pam_start in -lpam... yes
checking whether to enable mod_cap... no
checking ctype.h usability... yes
checking ctype.h presence... yes
checking for ctype.h... yes
checking getopt.h usability... yes
checking getopt.h presence... yes
checking for getopt.h... yes
checking crypt.h usability... no
checking crypt.h presence... no
checking for crypt.h... no
checking bstring.h usability... no
checking bstring.h presence... no
checking for bstring.h... no
checking for strings.h... (cached) yes
checking limits.h usability... yes
checking limits.h presence... yes
checking for limits.h... yes
checking for sys/types.h... (cached) yes
checking sys/mount.h usability... no
checking sys/mount.h presence... yes
configure: WARNING: sys/mount.h: present but cannot be compiled
configure: WARNING: sys/mount.h: check for missing prerequisite headers?
configure: WARNING: sys/mount.h: proceeding with the preprocessor's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to address@hidden ##
configure: WARNING:     ## ------------------------------------ ##
checking for sys/mount.h... yes
checking sys/param.h usability... yes
checking sys/param.h presence... yes
checking for sys/param.h... yes
checking sys/file.h usability... yes
checking sys/file.h presence... yes
checking for sys/file.h... yes
checking sys/uio.h usability... yes
checking sys/uio.h presence... yes
checking for sys/uio.h... yes
checking netdb.h usability... yes
checking netdb.h presence... yes
checking for netdb.h... yes
checking netinet/in.h usability... yes
checking netinet/in.h presence... yes
checking for netinet/in.h... yes
checking netinet/tcp.h usability... yes
checking netinet/tcp.h presence... yes
checking for netinet/tcp.h... yes
checking arpa/inet.h usability... yes
checking arpa/inet.h presence... yes
checking for arpa/inet.h... yes
checking for sys/stat.h... (cached) yes
checking errno.h usability... yes
checking errno.h presence... yes
checking for errno.h... yes
checking sys/socket.h usability... yes
checking sys/socket.h presence... yes
checking for sys/socket.h... yes
checking sys/termios.h usability... yes
checking sys/termios.h presence... yes
checking for sys/termios.h... yes
checking sys/termio.h usability... no
checking sys/termio.h presence... no
checking for sys/termio.h... no
checking sys/statvfs.h usability... yes
checking sys/statvfs.h presence... yes
checking for sys/statvfs.h... yes
checking sys/vfs.h usability... no
checking sys/vfs.h presence... no
checking for sys/vfs.h... no
checking sys/select.h usability... yes
checking sys/select.h presence... yes
checking for sys/select.h... yes
checking dirent.h usability... yes
checking dirent.h presence... yes
checking for dirent.h... yes
checking ndir.h usability... no
checking ndir.h presence... no
checking for ndir.h... no
checking sys/ndir.h usability... no
checking sys/ndir.h presence... no
checking for sys/ndir.h... no
checking sys/dir.h usability... yes
checking sys/dir.h presence... yes
checking for sys/dir.h... yes
checking vmsdir.h usability... no
checking vmsdir.h presence... no
checking for vmsdir.h... no
checking utmpx.h usability... no
checking utmpx.h presence... no
checking for utmpx.h... no
checking regex.h usability... yes
checking regex.h presence... yes
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checking syslog.h usability... yes
checking syslog.h presence... yes
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checking curses.h usability... yes
checking curses.h presence... yes
checking for curses.h... yes
checking ncurses.h usability... yes
checking ncurses.h presence... yes
checking for ncurses.h... yes
checking for an ANSI C-conforming const... yes
checking for inline... inline
checking for uid_t in sys/types.h... yes
checking for pid_t... yes
checking for size_t... yes
checking for mode_t... yes
checking for off_t... yes
checking type of array argument to getgroups... gid_t
checking for timer_t... yes
checking for short... yes
checking size of short... 2
checking for int... yes
checking size of int... 4
checking for long... yes
checking size of long... 4
checking for long long... yes
checking size of long long... 8
checking for off_t... (cached) yes
checking size of off_t... 8
checking whether time.h and sys/time.h may both be included... yes
checking whether struct tm is in sys/time.h or time.h... time.h
checking for umode_t... no
checking for ino_t... yes
checking for socklen_t... yes
checking utmp.h usability... yes
checking utmp.h presence... yes
checking for utmp.h... yes
checking whether your struct utmp has ut_user... no
checking whether your struct utmp has ut_host... yes
checking whether your struct utmp has ut_exit... no
checking whether your syslog.h defines LOG_CRON... yes
checking whether your syslog.h defines LOG_FTP... yes
checking for d_fd in DIR structure... no
checking for dd_fd in DIR structure... yes
checking for working alloca.h... no
checking for alloca... yes
checking for alloca in -lgen... no
checking whether gcc needs -traditional... no
checking whether setpgrp takes no argument... no
checking return type of signal handlers... void
checking for vprintf... yes
checking for _doprnt... no
checking for bcopy... yes
checking for crypt... yes
checking for fgetgrent... no
checking for fgetpwent... no
checking for flock... yes
checking for getcwd... yes
checking for gethostname... yes
checking for getopt... yes
checking for getopt_long... yes
checking for gettimeofday... yes
checking for inet_aton... yes
checking for memcpy... yes
checking for mempcpy... no
checking for mkdir... yes
checking for mkstemp... yes
checking for rmdir... yes
checking for select... yes
checking for setgroups... yes
checking for socket... yes
checking for statfs... yes
checking for strchr... yes
checking for strcoll... yes
checking for strerror... yes
checking for strsep... yes
checking for strtol... yes
checking for setprotoent... yes
checking for endprotoent... yes
checking for vsnprintf... yes
checking for snprintf... yes
checking for setsid... yes
checking for setgroupent... yes
checking for seteuid... yes
checking for setegid... yes
checking for siginterrupt... yes
checking for setpgid... yes
checking for regcomp... yes
checking for tzset... yes
checking for pathconf... yes
checking for fpathconf... yes
checking for fgetspent... no
checking for setpassent... yes
checking for initscr in -lcurses... yes
checking for initscr in -lncurses... yes
checking for setproctitle... yes
checking libutil.h usability... yes
checking libutil.h presence... yes
checking for libutil.h... yes
checking for setproctitle in -lutil... yes
configure: creating ./config.status
config.status: creating lib/Makefile
config.status: creating src/Makefile
config.status: creating modules/Makefile
config.status: creating utils/Makefile
config.status: creating Makefile
config.status: creating Make.rules
config.status: creating config.h
config.status: executing default commands
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