Multiple configurations and out of source building

It is possible to have multiple configurations for the same source at once. This is done using the out-of-source build support, also called VPATH building after the make variable used to support this feature.

Preparations

You only need to do this if you have earlier built a language in-source (the default). What you then need to do is:

cd $GTLANG ## ie lang-xxx
make distclean

That is, cd into the language you want to reconfigure, and run the command make distclean. This command will not only delete the files you have built, but also all the generated Makefile’s and other generated build files. This is necessary to not confuse the build system.

Multiple configurations for a single language

The basic idea is to create a separate build directory for each configuration you need, and call the configure script from there. Here is one possible setup:

cd $GTLANG ## ie lang-xxx
mkdir build
cd build
mkdir xerox
cd xerox
../../configure --without-hfst --with-xfst
make
cd ..
mkdir hfst
cd hfst
../../configure
make

We just created two build directories — xerox and hfst — within a common build directory. Within each of them we called the configure script with the options needed to build for only the fst implementation specified. Everything should work as usual, including make check.

A setup like this can be used to have multiple configurations for the different build types: for spellers only, for dictionaries only, for oahpa, etc. Using this type of build setup, it is also easy to compare different build times, to compare the output of fst’s from different configurations, etc., since the resulting fst’s are in different build trees, and thus aren’t overwritten by the next make.

This can also be used to turn off some of the default targets, to speed up the compilation process as much as possible for the targets one wants. Here is an example of how to configure for building spellers, and spellers only:

cd $GTLANG
mkdir build
cd build
mkdir spellers
cd spellers
../../configure --enable-spellers \
                --disable-syntax  \
                --disable-analysers \
                --disable-generators \
                --disable-transcriptors
make

This will turn off compilation of the regular analysers and generators, and will for some languages save considerable compilation time. A similar strategy can of course be put to use for other specialised targets like MT. (There seems to be some shortcomings that should be fixed, vislcg3 files and generated documentation seems to be built always irrespective of configuration options.)

NB! When using out-of-source (aka VPATH) building, the aliases usme, dsme, etc. do NOT work. This is because the aliases have hard-coded paths relative to $GTHOME/langs/. The plan is to replace the aliases with shell scripts, allowing us to test different locations for the fst files, and thus be able to handle such build setups in a more intelligent way.

Restrictions on VPATH building

There is really only one restriction:

You can not combine VPATH building with in-source building.

That is, you can’t have both a separate build/ directory and build directly within your $GTLANG/ directory. This means that as long as we rely on the aliases mentioned above, you can’t have both working aliases and VPATH building.