Use new features without breaking old module command¶

When working on large infrastructure, sometimes the module command is not deployed with the same version everywhere. You may have for instance some old cluster that still uses Modules version 3.2 and a newer supercomputer where the lastest version of Modules 4 is available. In such situation it may however be desired to share the same modulefile catalog.

People providing software that build software and generate the modulefiles to access them fall in a similar situation: a large variety of Modules version may be in use by the end-users of their build product.

This recipe describes how to use features from the latest version of Modules 4 in modulefiles without breaking the use of these modulefiles from older Modules version.

Implementation¶

The Tcl language provides some introspection mechanisms that help to know what Tcl procedures are available. In the modulefile or modulerc evaluation context, it helps to determine what Tcl modulefile commands are known. So by crafting a conditional test using such mechanism (with Tcl info commands command) it is possible to test if a new feature is available prior using it.

.modulerc¶

#%Module

# use module-hide only if available
if {[info commands module-hide] eq {module-hide}} {
   module-hide --after 2020-10-01 foo/1.1
}
# use module-forbid only if available
if {[info commands module-forbid] eq {module-forbid}} {
   module-forbid --after 2020-10-01 foo/1.1
}

Compatible with Modules v3.2+

Usage example¶

For this recipe, a foo module is available in version 1.1 and 1.2. Version 1.1 is outdated and it has been decided to hide and forbid it starting October 2020. For that, the new module-hide and module-forbid modulefile commands introduced in Modules 4.6 are used.

Enable the modulepath where the example modulefiles are located:

$ module use example/new-features-without-breaking-old-module/modulefiles

By using the conditional test code in the modulepath rc file (see Implementation section above), the two new modulefile commands are not used. So older versions of Modules still in use do not benefit from the dynamic hiding and forbidding features however no error are obtained on these setups:

$ module -V | grep ^VERSION=
VERSION=3.2.13
$ module avail -t foo
/path/to/example/new-features-without-breaking-old-module/modulefiles:
foo/1.1
foo/1.2

Yet the dynamic hiding and forbidding features are enabled for setup using Modules 4.6 or newer version:

$ module -V
Modules Release 4.6.0 (2020-09-16)
$ module avail -t foo
/path/to/example/new-features-without-breaking-old-module/modulefiles:
foo/1.2