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Wrapping dependencies

Since EasyBuild v3.7.0 a special-purpose generic easyblock named ModuleRC is available, which can be used to generate a (software-specific) .modulerc file (as opposed to generating an actual module file).


For compatibility with the different modules tools supported by EasyBuild (see Modules tool (--modules-tool)), the .modulerc file is always generated in Tcl syntax (for now), regardless of the module syntax that is used for module files. Only Lmod 7.8 (or later) supports .modulerc.lua files in Lua syntax.

The ModuleRC easyblock supports including module-version in the generated .modulerc file, which defines a so-called "symbolic version".

This can be used to install a "wrapper" for a particular module, which can be useful in the context of dependencies. For example, it can be used to avoid depending on a specific version of a particular software package by specifying the dependency only on the <major>.<minor> version instead (i.e., without including the "subminor" version, which usually corresponds to a bugfix release).

One particular example where this is employed is for Java. Since the 2018b generation of the Common toolchains, we use a wrapper for Java (e.g., Java/17), rather than depending on a specific version (e.g., Java/17.0.6):

# specify dependency on Java/17 "wrapper", rather than a specific Java version
dependencies = [('Java', '17', '', SYSTEM)]

This has a couple of advantages:

  • it helps with avoiding version conflicts on the Java dependency used by two (or more) otherwise independent module files;
  • it allows to perform an in-place update of the Java wrapper to a more recent Java (bugfix) release in the blink of an eye, since it only involves re-generating a .modulerc file (as opposed to performing actual installation and generating a module file); in addition, it doesn't require updating/re-generating existing module files that depend on the Java wrapper (since the version of the wrapper does not change)

Since ModuleRC is a generic easyblock , it can also be employed to install module "wrappers" for dependencies other than Java.