kubectl: remove usage info from bad flag msg, only print help tip

[sallyom]

/kind cleanup

What this PR does / why we need it:
kubectl cmds have many options/flags. When a user passes a bad flag, cmd should only output a tip to run --help, rather than print the usage info.

Which issue(s) this PR fixes:
Fixes #66572

Does this PR introduce a user-facing change?:

If a bad flag is supplied to a kubectl command, only a tip to run --help is printed, instead of the usage menu.  Usage menu is printed upon running `kubectl command --help`. 

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

Hi @sallyom. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[sallyom]

example with PR:

$ kubectl config --foo
Error: unknown flag: --foo
See 'kubectl config --help' for usage.

$ kubectl config view --foo
Error: unknown flag: --foo
See 'kubectl config view --help' for usage.

example without:

$ kubectl config --foo
Error: unknown flag: --foo


Available Commands:
  current-context Displays the current-context
  delete-cluster  Delete the specified cluster from the kubeconfig
  delete-context  Delete the specified context from the kubeconfig
  get-clusters    Display clusters defined in the kubeconfig
  get-contexts    Describe one or many contexts
  rename-context  Renames a context from the kubeconfig file.
  set             Sets an individual value in a kubeconfig file
  set-cluster     Sets a cluster entry in kubeconfig
  set-context     Sets a context entry in kubeconfig
  set-credentials Sets a user entry in kubeconfig
  unset           Unsets an individual value in a kubeconfig file
  use-context     Sets the current-context in a kubeconfig file
  view            Display merged kubeconfig settings or a specified kubeconfig file

Usage:
  kubectl config SUBCOMMAND [options]

Use "kubectl <command> --help" for more information about a given command.
Use "kubectl options" for a list of global command-line options (applies to all commands).

$ kubectl config view --foo
Error: unknown flag: --foo


Examples:
  # Show merged kubeconfig settings.
  kubectl config view
  
  # Show merged kubeconfig settings and raw certificate data.
  kubectl config view --raw
  
  # Get the password for the e2e user
  kubectl config view -o jsonpath='{.users[?(@.name == "e2e")].user.password}'

Options:
      --allow-missing-template-keys=true: If true, ignore any errors in templates when a field or map key is missing in the template. Only applies to golang and jsonpath output formats.
      --flatten=false: Flatten the resulting kubeconfig file into self-contained output (useful for creating portable kubeconfig files)
      --merge=true: Merge the full hierarchy of kubeconfig files
      --minify=false: Remove all information not used by current-context from the output
  -o, --output='yaml': Output format. One of: json|yaml|name|go-template|go-template-file|template|templatefile|jsonpath|jsonpath-file.
      --raw=false: Display raw byte data
      --template='': Template string or path to template file to use when -o=go-template, -o=go-template-file. The template format is golang templates [http://golang.org/pkg/text/template/#pkg-overview].

Usage:
  kubectl config view [flags] [options]

Use "kubectl options" for a list of global command-line options (applies to all commands).

[sallyom]

whoops kubectl options has disappeared, will fix. fixed

noticed kubectl options --foo needs a custom FlagErrorMsg, since options doesn't/shouldn't return a help menu

$ kubectl options --foo
unknown flag: --foo
Run 'kubectl options' without flags.

[eloyekunle]

/ok-to-test

[sallyom]

/test pull-kubernetes-integration

[soltysh]

I'd replace all of this with just:

func (templater *templater) FlagErrorFunc(exposedFlags ...string) func(*cobra.Command, error) error {
    return func(c *cobra.Command, err error) error {
        c.SilenceUsage = true
        return fmt.Errorf("%s\nSee '%s --help' for usage.", err, c.CommandPath())
    }
}

[sallyom]

😃 yup

[sallyom]

I've made the above change-it's much better, but with only this change something bugs me:

$ kubectl options --foo
Error: unknown flag: --foo
See 'kubectl options --help' for usage.

but kubectl options --help returns nothing.
I added a special case for the options --badflag to get:

$ kubectl options --foo
Error: unknown flag: --foo
Run 'kubectl options' without flags.

[soltysh]

Leave these as is, this way when you apply the previous suggestion and run just kubectl you'll get nice info what kubectl is, w/o it you won't. Compare yours output with:

$ kubectl
kubectl controls the Kubernetes cluster manager.

 Find more information at: https://kubernetes.io/docs/reference/kubectl/overview/
...

yours is missing above

[sallyom]

done

[sallyom]

thanks for the review @soltysh

[soltysh]

/lgtm
/approve
/priority important-longterm

[k8s-ci-robot]

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This pull-request has been approved by: sallyom, soltysh

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