feat: Install Plugins alongside Flux setup in gh actions

[gat786]

This PR adds the capability of installing plugins to the action which sets up Flux on a GH Action.

Closes: #5933

Adds two new variables to the GH Action input

• plugins: [optional] Plugins to install alongside Flux. One per line: <name>@<version|digest>.
  Example: mirror@0.0.1
• plugin_dir: [optional] Directory where the plugins should be installed, setups the FLUXCD_PLUGINS env variable.

And outputs

• plugin-dir - Directory where the plugin binaries are present. This helps in users know the directory even when it was unspecified and they can use this value for further processing if need be.

the plugin support comes with a feature gate which is designed to exit with an error when plugins were specified but the flux binary installed does not support plugins yet (i.e. it has a version < 2.9.0.

[gat786]

I did run some tests here -> https://github.com/gat786/flux2/actions/runs/28187933002

if it helps with anything!

[matheuscscp]

Hey @gat786, thanks very much for this PR!

We need to add an if: field to the plugin step so it runs only if inputs.plugins is specified.

Also, let's rename plugin_dir to plugin-dir, which is the GHA convention. We should also define a sensible default for this input, as people will probably not have an opinion about it. Finally, the effective plugin-dir should be an output of this action, because even though people will not want to think about it to choose one, they will still need the default directory chosen by the action e.g. for the mirror plugin, which for some commands expects the config file to be a sibling of the binary in the filesystem.

[matheuscscp]

Hey @gat786 please squash, rebase and force-push, this PR should have a single commit 🙏

[gat786]

@matheuscscp after a few back and forths me donez!

[matheuscscp]

Looks like the if: blocks are wrong, I think they don't need the ${{ and }}

[gat786]

oh no, lemme check

[gat786]

it is interesting that they do not allow using {{, as far as i remember it used to be a norm. In any case, I fixed that issue along with it I separated the code out a bit and tested it to make sure it doesn't break this time.

[matheuscscp]

Hey @gat786 this feature needs a very important gate: only the Flux CLI v2.9+ will support it. I think we need to detect the version and check if 2.9+ is satisfied, in order to print a nice error message about this requirement not being met, and that also shows the installed version.

[matheuscscp]

Also wondering why are the other env vars needed i.e. those beyond FLUXCD_PLUGINS

[gat786]

Hey the FLUXCD_PLUGINS is constructed using those other variables and when the other variables are not exported the construction does not happen properly, i.e. the os, arch and version entries remain empty.

I can remove the other exports by constructing fluxcd plugins directory in the same step as installation but since installation of plugins is going to be condition based I had to do it in its own step and for that exports need to happen.

[matheuscscp]

I think we can use step inputs/outputs for this, and not export envs. This way it stays internal.

[gat786]

Hey I added a feature gate and did some testing on it as well across platforms it does seem to work according to me, please check whenever you can!

[matheuscscp]

LGTM! 🚀

@gat786 Thanks very much for the contribution!

[gat786]

Thank you so much!

[gat786]

I would like to participate even more in the upcoming future! Learnt a lot from this implementation!