Re: [PATCH 3/3] gettext: fix implicit build result

[Ming Liu <ming.liu@windriver.com>]

On 07/17/2014 05:21 PM, Burton, Ross wrote:
> On 17 July 2014 08:58, Ming Liu <ming.liu@windriver.com> wrote:
>> Some "once only" variants are being defined instead of standard autoconf
>> macros, for instance, AC_CHECK_HEADERS_ONCE like AC_CHECK_HEADERS. The
>> advantage is that the check for each of the headers will be put only once
>> into the 'configure' file, therefore it keeps the size down. But there
>> is also a drawback that the checks then will turn to be statically inserted
>> to the configure and cannot be conditionalized any more. It will
>> definitely break the dependencies chosen as internally included.
> I'm confused as to why this breaks anything, and if it does break
> gettext then it's not embedded-specific but an upstream bug in the
> configure script, surely.  Can you explain what the problem is?
Yes, I'd like to explain it a little more.
AC_CHECK_HEADERS_ONCE will statically add some code to 'configure' file 
to force checking headers no matter it's in a condition or not. For example:
   ......
   if test "$gl_cv_libxml_use_included" != yes; then
     ......
     AC_CHECK_HEADERS_ONCE([somehead.h])
     ......
   fi

will always check somehead.h even gl_cv_libxml_use_included equal to 
'yes', then there will be a problem if we want to choose some 
dependency, for instance, libxml2, to be internally included, that means 
not refer to any headers or libraries in system, but oppositely, 
AC_CHECK_HEADERS_ONCE will pull in the header that it's supposed to 
check, and that would break the dependency we intended to set.

//Ming Liu
>
> Ross
>
>