Hi, We found an odd side effect of gnulib's absolute_header.m4 over on the Autoconf mailing list ( http://lists.gnu.org/archive/html/autoconf/2008-08/msg00024.html). Within an Autoconf macro, modifying CPPFLAGS, calling AC_CHECK_HEADER, and then calling gl_ABSOLUTE_HEADER prevents the header check from using the updated CPPFLAGS value.
The expansion of gl_ABSOLUTE_HEADER causes the function look for the header before CPPFLAGS is modified. Then, after CPPFLAGS changes and AC_CHECK_HEADER does occur, the previously cached "no" result is used. A recreate: 1. Snag absolute_header.m4 from http://cvs.savannah.gnu.org/viewvc/*checkout*/gnulib/m4/absolute-header.m4?root=gnulib&content-type=text/plain 2. Pick your favorite Makefile.am. 3. Use this configure.ac: AC_INIT(recreate, 0.0.1, [EMAIL PROTECTED]) > AM_CONFIG_HEADER(config.h) > AM_INIT_AUTOMAKE(1.9 -Wall -Werror foreign) > AC_PREREQ([2.61]) > > AC_DEFUN([AX_TRILINOS_BASE],[ > if test -n "${TRILINOS_HOME}"; then CPPFLAGS="-I${TRILINOS_HOME}/include $CPPFLAGS" > fi > > AC_MSG_NOTICE([DEBUG: CPPFLAGS=${CPPFLAGS}]) > AC_CHECK_HEADER([Trilinos_version.h],[found_header=yes]) > > if test "$found_header" = yes; then > gl_ABSOLUTE_HEADER([Trilinos_version.h]) > AC_DEFINE(HAVE_TRILINOS,1,[Define if Trilinos is available]) > else > AC_MSG_ERROR([Trilinos_version.h not found]) > fi > ]) > AX_TRILINOS_BASE > > AC_CONFIG_FILES([ > Makefile > ]) > AC_OUTPUT() > 4. Invoke 'TRILINOS_HOME=somewhere ./configure' 5. Look at config.log and observe that the failed Trilinos_version.h check did not use the DEBUG: CPPFLAGS=-Isomewhere value displayed in step #4. To workaround the issue, choose any of: 1. Remove gl_ABSOLUTE_HEADER([Trilinos_version.h]) from AX_TRILINOS_BASE 2. Move the gl_ABSOLUTE_HEADER call outside of AX_TRILINOS_BASE into the toplevel configure.ac. 3. Move the gl_ABSOLUTE_HEADER call into a separate function that isn't AX_TRILINOS_BASE. But, you cannot call the new, separate function from within AX_TRILINOS_BASE otherwise you hit the same issue. 4. Remove the function AX_TRILINOS_BASE and just dump the function's code into the main configure.ac file. - Rhys
