module reload changes path ordering

[ben-bowers]

Describe the bug

Path ordering is different before and after a module reload, which was unexpected.

To Reproduce

Steps to reproduce the behavior:

$ echo $MYPATH

$ module load FOOFOO
Loading FOOFOO
  Loading requirement: BARBAR
$ echo $MYPATH
/home/BAR:/home/FOO
$ module reload
$ echo $MYPATH
/home/FOO:/home/BAR

Location and content of any modulerc or modulefile involved:

$ cat FOOFOO
#%Module1.0 # -*- tcl -*-
prepend-path MYPATH /home/FOO
module load BARBAR

$ cat BARBAR
#%Module1.0 # -*- tcl -*-
prepend-path MYPATH /home/BAR

Expected behavior

$MYPATH path variable consistent before and after reload

Error and debugging information

$ module --debug <command1> <arguments>
$ module --debug <command2> <arguments>
...

Modules version and configuration

$ module --version
Modules Release 5.0.0 (2021-09-12)
# The same behavior exists in 4.3.x, 4.5.x and 4.6.x as well.

Additional context

It is worth noting that if all prepend-paths above are changed to append-path then the same ordering issue occurs.

[xdelaruelle]

The order of commands in FOOFOO modulefile is not consistent with the resulting load order: BARBAR is loaded before FOOFOO but MYPATH prepend is achieved in FOOFOO prior this requirement load.

When reloading, environment changes are made consistent to the loading order (unload FOOFOO, unload BARBAR, load BARBAR, load FOOFOO), so the environment variable changes triggered by FOOFOO are applied last. Same behavior is observed if BARBAR modulefile is already loaded prior attempting to load FOOFOO modulefile.

To achieve consistency, the load of requirements should be done prior any environment changes. So in this example, module load BARBAR should be done prior the prepend-path MYPATH command.

[ben-bowers]

To achieve consistency, the load of requirements should be done prior any environment changes.

Your explanation makes sense in context of how the reload currently works. I had mistakenly thought that a reload would work similarly to what would happen if using a module purge ; module load FOOFOO, as BARBAR is loaded from inside FOOFOO.

I don't think I previously understood that prepend/append-path must come before any module load commands in a modulefile - is this documented somewhere?

In any event, I think this particular case is an attempt to arrange elements in $PATH in a specific order (the FOOFOO/BARBAR sample is a reduced testcase using $MYPATH to be more obvious), so I will need to re-think how I am sequencing things in light of loading multiple modulefiles.

[xdelaruelle]

I don't think I previously understood that prepend/append-path must come before any module load commands in a modulefile - is this documented somewhere?

Should come after requirement specification (module load/prereq). I will improve the documentation on that point, I am quite sure this is not well documented currently.

[ben-bowers]

Oops I said that incorrectly. My understanding is now that the sequence of module load / prereq (1st) and prepend-path / append-path (2nd) directives in the modulefile is important if reloading is ever going to be done