I think it's fine to add the knob for suppressing warnings to kustomize as a library. I don't think we should add this knob to the kustomize binary, but folks who are integrating kustomize as a library into their own tool may have reasons to suppress these, particularly if the use of kustomize is an implementation detail that they might not want to expose to users.

/triage accepted
/kind feature
/help

@natasha41575:
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I implemented a code snippet to try to reproduce the warning traces, however this code does not prints any warning:

import (
	"log"
	"os"

	"sigs.k8s.io/kustomize/api/krusty"
	"sigs.k8s.io/kustomize/kyaml/filesys"
)

func main() {
	writer := os.Stdout

	k := krusty.MakeKustomizer(krusty.MakeDefaultOptions())

	fSys := filesys.MakeFsOnDisk()
	m, err := k.Run(fSys, "/ABSOLUTE/PATH/kustomization-foo")
	if err != nil {
		log.Fatalf("Error: %v", err)
		return
	}

	yaml, err := m.AsYaml()
	if err != nil {
		log.Fatalf("Error: %v", err)
		return
	}

	_, err = writer.Write(yaml)
	if err != nil {
		log.Fatalf("Error: %v", err)
		return
	}
}

kustomization-foo contains the "hello world" example: https://github.com/kubernetes-sigs/kustomize/tree/master/examples/helloWorld

@natasha41575 Is this the way to import kustomize as a lib? I'm interested on fix this issue

Thanks a lot!

/assign

I reviewed again the code, and perhaps these flags should be suppressed with a knob when used as lib:

https://github.com/davidbaena/kustomize/blob/790ca0e7b66aae32c4ab6258709f15be471b15b4/kustomize/commands/build/build.go#L112

	msg := "Error marking flag '%s' as deprecated: %v"
	err := cmd.Flags().MarkDeprecated(flagReorderOutputName,
		"use the new 'sortOptions' field in kustomization.yaml instead.")
	if err != nil {
		log.Fatalf(msg, flagReorderOutputName, err)
	}
	err = cmd.Flags().MarkDeprecated(managedByFlag,
		"The flag `enable-managedby-label` has been deprecated. Use the `managedByLabel` option in the `buildMetadata` field instead.")
	if err != nil {
		log.Fatalf(msg, managedByFlag, err)
	}

Do you mean these warnings?

It's emiited in https://github.com/kubernetes-sigs/kustomize/blob/master/api/internal/target/kusttarget.go#L70 and directly to stderr. Ideally it should take a logger (like slog.Logger) and the caller could pass a caller here.

Ok, I'm going to implement that solution
Thanks!

This issue has been implemented in this PR:
#5466