STAR_SUPPRESS_BUILD_IF(test, message)
Some components should be built only conditionally, if
certain conditions apply. For example, the
sgmlkit component can be built only if the
host system has jade installed on it, but the
lack of this is not an error, in the sense that
it should cause a tree-wide ./configure to
fail. This macro helps with this situation.
If this macro is triggered, by the given condition
being true, then ./configure,
make and make install
will all succeed without compiling anything, with
the latter installing a correctly formed manifest file
which does not list any installed files.
The test in the first argument is a shell
expression which should evaluate to true (ie, return a
zero status) if the build should be suppressed. In the
case of the sgmlkit component, the
configure.ac includes the lines:
AC_PATH_PROGS(JADE, [openjade jade], NOJADE)
AC_PATH_PROGS(SGMLNORM, [osgmlnorm sgmlnorm], NOSGMLNORM)
...
STAR_SUPPRESS_BUILD_IF([test $JADE = NOJADE -o $SGMLNORM = NOSGMLNORM],
[JADE=$JADE, SGMLNORM=$SGMLNORM: both needed for sgmlkit])
test expression evaluates to true if
either of the $JADE or $SGMLNORM
variables has the special values given as defaults in the
AC_PATH_PROGS macros earlier.If the test is true, the message is displayed during the
./configure run, but the configuration does
not fail. Instead, a stamp file
STAR_SUPPRESS_BUILD is left in the build
directory, with the consequence that if you subsequently
type make, that build will do nothing, emit the
same message, and also not fail. If you subsequently
invoke make install, that will also succeed,
but install no files, except a manifest without a
<files> element.
If you do any special installation work in your
Makefile.am, remember to check for the
existence of this stamp file, and make sure that you do
not actually install anything if the file is present.
The difference between this and the standard
AC_FATAL macro is that the latter is for an
error in the configuration script -- either a logic error
there, or a serious problem like being unable to compile
anything at all! Alternatively, if a dependency should be
present because it is listed in the
configure.ac as such, but it isn't, that's a
case for a call to AC_FATAL. The
STAR_SUPPRESS_BUILD_IF macro is for rather
more well-mannered interactions with the user, indicating
that there is other work they might have to do to get this
component building.
You should use this macro rather sparingly. If a component depends on a component thus suppressed, there will likely be trouble.