present but cannot be compiled (Was: Configure warning with curl-7.10.3)

[Akim Demaille]

Please, report this to the package maintainers, as it's a configure.ac
problem.  The Autoconf 2.57 doc says:

      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
   ])

Thanks!

| When configuring curl-7.10.3 on a solaris 8 system mostly up to date with
| patches, using gcc 3.2 from www.sunfreeware.com, I get the following warning:
| 
| checking net/if.h usability... no
| checking net/if.h presence... yes
| configure: WARNING: net/if.h: present but cannot be compiled
| configure: WARNING: net/if.h: check for missing prerequisite headers?
| configure: WARNING: net/if.h: proceeding with the preprocessor's result
| configure: WARNING:     ## ------------------------------------ ##
| configure: WARNING:     ## Report this to address@hidden ##
| configure: WARNING:     ## ------------------------------------ ##
| checking for net/if.h... yes
| checking netinet/in.h usability... yes
| checking netinet/in.h presence... yes
| checking for netinet/in.h... yes
| checking netinet/if_ether.h usability... no
| checking netinet/if_ether.h presence... yes
| configure: WARNING: netinet/if_ether.h: present but cannot be compiled
| configure: WARNING: netinet/if_ether.h: check for missing prerequisite 
headers?
| configure: WARNING: netinet/if_ether.h: proceeding with the preprocessor's 
result
| configure: WARNING:     ## ------------------------------------ ##
| configure: WARNING:     ## Report this to address@hidden ##
| configure: WARNING:     ## ------------------------------------ ##
| 
| 
| 
| The error messages from config.log are:
| 
| configure:13938: checking net/if.h usability
| configure:13951: gcc -c -g -O2  conftest.c >&5
| In file included from configure:14027:
| /usr/include/net/if.h:225: field `ifa_addr' has incomplete type
| /usr/include/net/if.h:227: field `ifu_broadaddr' has incomplete type
| /usr/include/net/if.h:228: field `ifu_dstaddr' has incomplete type
| /usr/include/net/if.h:234: confused by earlier errors, bailing out
| 
| configure:13938: checking netinet/if_ether.h usability
| configure:13951: gcc -c -g -O2  conftest.c >&5
| In file included from 
/usr/local/lib/gcc-lib/sparc-sun-solaris2.8/3.2/include/ne
| tinet/if_ether.h:37,
|                  from configure:14029:
| /usr/include/net/if_arp.h:61: field `arp_pa' has incomplete type
| /usr/include/net/if_arp.h:62: field `arp_ha' has incomplete type
| /usr/include/net/if_arp.h:64: confused by earlier errors, bailing out
| 
| 
| gcc -v gives:
| Reading specs from /usr/local/lib/gcc-lib/sparc-sun-solaris2.8/3.2/specs
| Configured with: ../configure --with-as=/usr/ccs/bin/as 
--with-ld=/usr/ccs/bin/ld --disable-nls
| Thread model: posix
| gcc version 3.2
| 
| 
| Compilation succeeded, and it appears to be working without a problem.
| I still have the configure logs, config.h etc if they're any help.