[ci] conda-based CI jobs broken: "conda/activate.d/libarrow_activate.sh: line 25: CONDA_BUILD: unbound variable"

[jameslamb]

Description

CI jobs using conda are currently breaking like this:

/Users/runner/miniforge/envs/test-env/etc/conda/activate.d/libarrow_activate.sh: line 25: CONDA_BUILD: unbound variable

Reproducible example

Any Python-package CI jobs using conda in the last few hours. See, for example https://github.com/microsoft/LightGBM/actions/runs/12943275214/job/36157521507?pr=6668

Environment info

N/A

Additional Comments

It looks like this has happened to others in the past, guess we've just been lucky here:

• “unbound variable” ERROR when conda invoked within bash scripts containing command “set -u” conda/conda#9966
• activate breaks on unbound vars in some bash shells conda/conda#3200
• Shell (bash) scripts are not compatible with -e and -u options ContinuumIO/anaconda-issues#8838

It looks like this can happen when using bash with set -u and then calling source activate or similar.

[jameslamb]

Ah, think I found the root cause: conda-forge/arrow-cpp-feedstock#1694

[jameslamb]

I put up a proposed fix in conda-forge/arrow-cpp-feedstock#1696 ... let's see if that's accepted before adding workarounds like #6800

[jameslamb]

Seeing CI starting to pass across the project, so I do think that upstream fix resolved this!

Closing this and #6800