I do not think we should do for logging. Instead of that, why we can not just use slice?

frsNeedPreemption.UnsortedList()

@mimowo Did you indicate JsonMarshal proposed in this PR? If yes, what is the reason not to use slice?

Actually, my suggestion was to use slice rather than Json, for sure. I was just thinking about exposing this via String function, but frsNeedPreemption.UnsortedList() is also neat. I'm ok either way.

Actually yes, it looks like logger manages to marshal frsNeedPreemption.UnsortedList() just fine, and using String() for FlavorResourceSet I still need to do marshalling somehow. So I can substitute frsNeedPreemption with frsNeedPreemption.UnsortedList() in klog calls just fine. Moreover, it works even when FlavorResource and FlavorResourceQuantities do not implements String().

However the line

I also see klog.KObj(preemptionCtx.preemptor.Obj) in klog calls, maybe this could be relevant?

still leads to the "json: unsupported type: resources.FlavorResourceQuantities" error (even when FlavorResource and FlavorResourceQuantities implement String())

Yeah, this is surprising - I was assuming adding String() for resources.FlavorResourceQuantities would be enough, as the logger should check the input type implementes the Stringer interface and call String(), we had a similar case here: kubernetes/kubernetes#121392 (comment)

I can trace that e.assignment is passed to the logger here:

The type entry is defined here:

And e.assignment is of type Assignment from here:

Maybe logger supports structs like:

type FlavorResource struct {
	Flavor   kueue.ResourceFlavorReference
	Resource corev1.ResourceName
}

But not map[FlavorResource]int64 out of the box? That's just one guess.

Not sure if this helps much, but you can setup also debugger in vs-code for the integration tests.

My setup for the settings.json in vs-code you just need to set:

    "go.testEnvVars": {
        "KUBEBUILDER_ASSETS": "/usr/local/..**../kubebuilder-envtest/k8s/1.28.3-linux-amd64",
    },

The full value of the var for your setup should be printed when invoking make test-integration target.