==== Use SPack on Minerva ====

[[https://spack.readthedocs.io/en/latest/index.html|SPack]] is a package manager that provides a "modules" interface, able to handle multiple versions, dependencies, and build environments.
It can be used together with, or as a replacement for, the old modules environment that has been used for a long time.

To use the latest SPack repository on Minerva (there are some older ''/home/SPACK*'' left), you must **source** a config file:

  . /home/SPACK2021/share/spack/setup-env.sh

After that, you may use ''spack help''. Most important commands I use:
  * ''spack list hdf5'' to find (source) packages matching ''hdf5''
  * ''spack info hdf5'' to show the description of the ''hdf5'' (source) package
  * ''spack find hdf5'' to check whether the package has already been built and installed (as binary and module)
  * ''spack find -lv hdf5'' provides more details:
    * green: compiler version
    * cyan: package version
    * pale blue: variants user to build (''~'' prefixes disabled, ''+'' enabled variants)
    * gray: package hash
  * ''spack find ... -d hdf5'' lists the (build) dependencies

You will have to make yourself familiar with the special characters used:
  * ''+'' enables a variant, ''~'' disables it
  * ''^'' specifies a build include
  * ''%'' denotes a compiler, ''@'' a version
  * ''/'' can be used to select hashes

To load the ''o2x4itb    hdf5@1.8.19~cxx~debug~fortran~hl+mpi+pic+shared~szip~threadsafe'' built with ''%gcc@7.3.0'' you saw listed with the last ''find'' command, you may choose from the following options:
  * ''module load hdf5-1.8.19-gcc-7.3.0-o2x4itb'' (old style, module name combines from //${packagename}-${packageversion}-${compiler}-${compilerversion}-${hash}//) or
  * ''spack load hdf5 ~cxx +mpi'' works (at the time of this writing)
  * ''spack load hdf5 /o2x4'' (with the hash further shortened) will also get the right one. //This even works without a package name!//
  * ''spack load hdf5 %gcc@7.3.0 +mpi'' will **match** (and load, although the docs suggest that an error would result!) **multiple modules**! //Don't forget to ''module (purge|unload)''!//

In general, ''spack load'' is slow, and prone to ambiguity errors. Use ''module list -t'' to identify such situations, and get the names of loaded modules one-per-line.
Package dependencies **are now resolved automatically** (even if not invoked with ''-r'').


**IMPORTANT: The ''/home/SPACK2021/'' tree is read-only** (and there are no means yet to make it collaborative)**. Therefore ''spack install'' will not work for you! If you need a package that hasn't been installed yet, ask me (Steffen), if possible keep the right options (variants, includes) at hand!**

(To be extended.)