Re-introduce removed kubectl --dry-run values.

For 1.23, we removed the kubectl `--dry-run` empty default value (`--dry-run`)
and boolean values (`--dry-run=true` and `--dry-run=false`). This change
required requiring users to specify `--dry-run=client` or `--dry-run=server`
due to a deprecation. This change was made in #105327.

After reconsideration, this change is not worth the churn for users.
It's likely that many users rely on these values for automated and manual use
cases.

This change reverts #105327 and re-introduces the values `--dry-run`,
`--dry-run=true`, and `--dry-run=false`.

staging/src/k8s.io/kubectl/pkg/cmd/util/helpers.go

@@ -23,6 +23,7 @@ import (
 	"io"
 	"net/url"
 	"os"
+	"strconv"
 	"strings"
 	"time"
 
@@ -546,18 +547,30 @@ const (
 
 func GetDryRunStrategy(cmd *cobra.Command) (DryRunStrategy, error) {
 	var dryRunFlag = GetFlagString(cmd, "dry-run")
-	switch dryRunFlag {
-	case cmd.Flag("dry-run").NoOptDefVal:
-		return DryRunNone, errors.New(`--dry-run flag without a value was specified. A value must be set: "none", "server", or "client".`)
-	case "client":
-		return DryRunClient, nil
-	case "server":
-		return DryRunServer, nil
-	case "none":
-		return DryRunNone, nil
-	default:
-		return DryRunNone, fmt.Errorf(`Invalid dry-run value (%v). Must be "none", "server", or "client".`, dryRunFlag)
+	b, err := strconv.ParseBool(dryRunFlag)
+	// The flag is not a boolean
+	if err != nil {
+		switch dryRunFlag {
+		case cmd.Flag("dry-run").NoOptDefVal:
+			klog.Warning(`--dry-run is deprecated and can be replaced with --dry-run=client.`)
+			return DryRunClient, nil
+		case "client":
+			return DryRunClient, nil
+		case "server":
+			return DryRunServer, nil
+		case "none":
+			return DryRunNone, nil
+		default:
+			return DryRunNone, fmt.Errorf(`Invalid dry-run value (%v). Must be "none", "server", or "client".`, dryRunFlag)
+		}
 	}
+	// The flag was a boolean
+	if b {
+		klog.Warningf(`--dry-run=%v is deprecated (boolean value) and can be replaced with --dry-run=%s.`, dryRunFlag, "client")
+		return DryRunClient, nil
+	}
+	klog.Warningf(`--dry-run=%v is deprecated (boolean value) and can be replaced with --dry-run=%s.`, dryRunFlag, "none")
+	return DryRunNone, nil
 }
 
 // PrintFlagsWithDryRunStrategy sets a success message at print time for the dry run strategy

test/cmd/apply.sh

@@ -101,6 +101,7 @@ run_kubectl_apply_tests() {
   kube::test::get_object_assert pods "{{range.items}}{{${id_field:?}}}:{{end}}" ''
 
   # apply dry-run
+  kubectl apply --dry-run=true -f hack/testdata/pod.yaml "${kube_flags[@]:?}"
   kubectl apply --dry-run=client -f hack/testdata/pod.yaml "${kube_flags[@]:?}"
   kubectl apply --dry-run=server -f hack/testdata/pod.yaml "${kube_flags[@]:?}"
   # No pod exists

test/cmd/batch.sh

@@ -49,7 +49,7 @@ run_job_tests() {
   kube::test::describe_resource_chunk_size_assert cronjobs events "--namespace=test-jobs"
 
   ### Create a job in dry-run mode
-  output_message=$(kubectl create job test-job --from=cronjob/pi --dry-run=client --namespace=test-jobs -o name)
+  output_message=$(kubectl create job test-job --from=cronjob/pi --dry-run=true --namespace=test-jobs -o name)
   # Post-condition: The text 'job.batch/test-job' should be part of the output
   kube::test::if_has_string "${output_message}" 'job.batch/test-job'
   # Post-condition: The test-job wasn't created actually