kubectl: add deprecation notice to flag usage help

Several klog flags were deprecated in Kubernetes 1.23, but that was not visible
in "kubectl options" because it does its own formatting without considering a
flag's deprecation string.

Now the output looks like this:

$ go run ./cmd/kubectl options
The following options can be passed to any command:

      --add-dir-header=false: If true, adds the file directory to the header of the log messages (DEPRECATED: will be
removed in a future release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --alsologtostderr=false: log to standard error as well as files (DEPRECATED: will be removed in a future release,
see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --as='': Username to impersonate for the operation. User could be a regular user or a service account in a
namespace.
      --as-group=[]: Group to impersonate for the operation, this flag can be repeated to specify multiple groups.
      --cache-dir='/home/pohly/.kube/cache': Default cache directory
      --certificate-authority='': Path to a cert file for the certificate authority
      --client-certificate='': Path to a client certificate file for TLS
      --client-key='': Path to a client key file for TLS
      --cluster='': The name of the kubeconfig cluster to use
      --context='': The name of the kubeconfig context to use
      --insecure-skip-tls-verify=false: If true, the server's certificate will not be checked for validity. This will
make your HTTPS connections insecure
      --kubeconfig='': Path to the kubeconfig file to use for CLI requests.
      --log-backtrace-at=:0: when logging hits line file:N, emit a stack trace (DEPRECATED: will be removed in a future
release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --log-dir='': If non-empty, write log files in this directory (DEPRECATED: will be removed in a future release,
see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --log-file='': If non-empty, use this log file (DEPRECATED: will be removed in a future release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --log-file-max-size=1800: Defines the maximum size a log file can grow to. Unit is megabytes. If the value is 0,
the maximum file size is unlimited. (DEPRECATED: will be removed in a future release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --log-flush-frequency=5s: Maximum number of seconds between log flushes
      --logtostderr=true: log to standard error instead of files (DEPRECATED: will be removed in a future release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --match-server-version=false: Require server version to match client version
  -n, --namespace='': If present, the namespace scope for this CLI request
      --one-output=false: If true, only write logs to their native severity level (vs also writing to each lower
severity level) (DEPRECATED: will be removed in a future release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --password='': Password for basic authentication to the API server
      --profile='none': Name of profile to capture. One of (none|cpu|heap|goroutine|threadcreate|block|mutex)
      --profile-output='profile.pprof': Name of the file to write the profile to
      --request-timeout='0': The length of time to wait before giving up on a single server request. Non-zero values
should contain a corresponding time unit (e.g. 1s, 2m, 3h). A value of zero means don't timeout requests.
  -s, --server='': The address and port of the Kubernetes API server
      --skip-headers=false: If true, avoid header prefixes in the log messages (DEPRECATED: will be removed in a future
release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --skip-log-headers=false: If true, avoid headers when opening log files (DEPRECATED: will be removed in a future
release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --stderrthreshold=2: logs at or above this threshold go to stderr (DEPRECATED: will be removed in a future
release, see
https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --tls-server-name='': Server name to use for server certificate validation. If it is not provided, the hostname
used to contact the server is used
      --token='': Bearer token for authentication to the API server
      --user='': The name of the kubeconfig user to use
      --username='': Username for basic authentication to the API server
  -v, --v=0: number for the log level verbosity
      --vmodule=: comma-separated list of pattern=N settings for file-filtered logging
      --warnings-as-errors=false: Treat warnings received from the server as errors and exit with a non-zero exit code

For comparison, pflag itself prints:

$ go run ./cmd/kubelet --help 2>&1 | grep -e --log-file
      --log-file string                                          If non-empty, use this log file (DEPRECATED: will be removed in a future release, see https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)
      --log-file-max-size uint                                   Defines the maximum size a log file can grow to. Unit is megabytes. If the value is 0, the maximum file size is unlimited. (default 1800) (DEPRECATED: will be removed in a future release, see https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components)

Kubernetes-commit: 21bd4ae18b5a146c8ef6dff373732abdecf60d66

pkg/util/templates/templater.go

@@ -225,10 +225,10 @@ func flagsUsages(f *flag.FlagSet) string {
 		if flag.Hidden {
 			return
 		}
-		format := "--%s=%s: %s\n"
+		format := "--%s=%s: %s%s\n"
 
 		if flag.Value.Type() == "string" {
-			format = "--%s='%s': %s\n"
+			format = "--%s='%s': %s%s\n"
 		}
 
 		if len(flag.Shorthand) > 0 {
@@ -237,7 +237,12 @@ func flagsUsages(f *flag.FlagSet) string {
 			format = "   %s   " + format
 		}
 
-		fmt.Fprintf(x, format, flag.Shorthand, flag.Name, flag.DefValue, flag.Usage)
+		deprecated := ""
+		if flag.Deprecated != "" {
+			deprecated = fmt.Sprintf(" (DEPRECATED: %s)", flag.Deprecated)
+		}
+
+		fmt.Fprintf(x, format, flag.Shorthand, flag.Name, flag.DefValue, flag.Usage, deprecated)
 	})
 
 	return x.String()