Optional conda dependencies

[forsyth2]

For #25, there was an issue raised over compatibility with the E3SM Unified environment:

mean climate metrics and modes of variability can be enabled, ENSO metrics still reply on CDAT, and will be enabled later.

That is, to avoid a CDAT dependency, we're planning to disable the ENSO task for now. However, that requires an optional dependency (i.e., if package A depends on package B, which depends on package C, but A doesn't use C's added functionality, do not install C).

# Let's look at what's in my conda environment for zppy-interfaces for this PR:
conda list -n zi-pcmdi-diags-20250917 > zi-pcmdi-diags-20250917_packages.txt
# Includes:
# cdat_info                 8.2.1              pyhd8ed1ab_3    conda-forge
# cdms2                     3.1.5           py310h4f3777b_25    conda-forge
# cdtime                    3.1.4           py310h7a088e3_13    conda-forge
# cdutil                    8.2.1              pyhd8ed1ab_5    conda-forge
# enso_metrics              1.1.5           py310hff52083_0    conda-forge
# libcdms                   3.1.2              hacc84be_132    conda-forge
# pcmdi_metrics             3.9.2              pyhd8ed1ab_0    conda-forge

conda search --info pcmdi_metrics=3.9.2
# dependencies:
#   - enso_metrics

conda search --info enso_metrics=1.1.5
# dependencies: 
#   - cdms2
#   - cdutil

conda search --info cdms2
# dependencies:
#   - cdat_info
#   - cdtime 3.*
#   - libcdms 3.*
conda search --info cdutil
#   - cdat_info
#   - cdms2

So, the dependency chain is zppy-interfaces-> pcmdi_metrics -> enso_metrics -> {cdms2, cdutil}

So, two things to do:

1. pcmdi_metrics appears to have a required dependency rather than an optional dependency on enso_metrics. This conflicts with a message from @lee1043 stating " in the newer PMP version (>=3.9.2) I have set the ENSO package as an optional dependency to PMP. I consider this as a temporary solution and expect it will be back to default dependency, once ENSO package’s CDAT-removal conversion completes." And as seen above, I'm using PMP 3.9.2. Also, conda search --info pcmdi_metrics=3.9.2 shows timestamp : 2025-09-10 22:21:37 UTC, which would include the changes of Remove cdat -- clean up PCMDI/pcmdi_metrics#1321. So, in theory, this should in fact be an optional dependency.
2. In Add pcmdi #25, add toggle code around any uses of the enso set so that the feature can be turned on/off. (NOTE: I suppose it's possible that because this step hasn't yet been done, conda is recognizing that the code still has this dependency, but Claude suggests Conda isn't that smart: "So yes - any "optional" dependency your code successfully uses is only there because some package in your dependency chain declared it as required, not because conda figured out you needed it." )

@lee1043 @tomvothecoder @xylar -- do you have any thoughts here? I haven't worked with optional dependencies before, so it's unclear if the dependency is set up wrong or if my environment or dev.yml is set up wrong.

[lee1043]

It looks like inclusion of enso_metrics from conda search might have caused by missing removal of it from PMP's conda feedstock (https://github.com/conda-forge/pcmdi_metrics-feedstock/blob/ddc8f4a1666e840c2917c29f68c425a9cea7a262/recipe/meta.yaml#L46). Let me update the conda feedstock accordingly.

[lee1043]

Just updated PMP's conda feedstock (conda-forge/pcmdi_metrics-feedstock#51). @forsyth2 could you check if that resolves the issue?

[xylar]

As I commented, conda-forge/pcmdi_metrics-feedstock#51 (comment), the build number did not get bumped. @lee1043, unfortunately you'll have to make another PR where you bump the build number (and you don't have to make any other change).

[lee1043]

I am in the process of releasing PMP v3.9.3 -- note, v3.9.3 removes CDAT dependencies, but still on python 3.10. I am preparing 4.0.0_alpha version which uses python 3.11 and higher version.