Issue 652: Add instance placement scriptlet extension

[christina-zh]

PR for #652
We were unable to validate our changes could you please validate for us?

[stgraber]

Hey, just wanted to let you know that I'm not ignoring this one, I'm just traveling and don't have easy access to test clusters to validate the logic, at worst I'll be able to do it on Monday.

[christina-zh]

Hey, just wanted to let you know that I'm not ignoring this one, I'm just traveling and don't have easy access to test clusters to validate the logic, at worst I'll be able to do it on Monday.

Ok sounds good, thank you for your time!

[stgraber]

Looking into this one now:

• Did a quick rebase due to conflicts introduced by changes we merged since
• Ran gofmt -s -w ./ to fix some code style issues
• Ran make static-analysis to check the rest and fixed the issues it identified

I'll take a closer look at the logic in both functions and do a bit of testing on this next.

[stgraber]

There seems to be some issues with the logic, it effectively requires the arguments instead of having them be optional.

Error: Failed instance creation: Failed instance placement scriptlet: Failed to run: get_instances: missing argument for project
Error: Failed instance creation: Failed instance placement scriptlet: Failed to run: get_cluster_members: missing argument for group

[stgraber]

I'll look at fixing those, shouldn't be too hard, I think I'll also add a 3rd function to the list as it'd be handy for one of my own clusters.

[christina-zh]

ok, thank you so much!

[stgraber]

Right, so what I had to do was:

• Only call UnpackArgs once per function
• Mark optional arguments with ?? per https://pkg.go.dev/go.starlark.net/starlark#UnpackArgs
• Re-shuffle the GetInstances logic a bit to only pass in a filter if either location or project was set

[stgraber]

Ended up filing #811 for the extra bit

[aanderse]

thank you so much for working on this @christina-zh and @stgraber!