Merge pull request #60675 from timoreimann/support-dry-run-in-kubectl-patch

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Add support for --dry-run to kubectl patch.

**What this PR does / why we need it**:

Add support for the `--dry-run` flag to `kubectl patch`. This is helpful to be able to preview patches prior to applying them.

**Which issue(s) this PR fixes**:
Refs #11488

**Special notes for your reviewer**:

This PR carries #45712.

**Release note**:
```release-note
`kubectl patch` now supports `--dry-run`.
```

pkg/kubectl/cmd/patch.go

@@ -30,7 +30,6 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apimachinery/pkg/types"
-	"k8s.io/apimachinery/pkg/util/json"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/strategicpatch"
 	"k8s.io/apimachinery/pkg/util/yaml"
@@ -50,6 +49,7 @@ type PatchOptions struct {
 	resource.FilenameOptions
 
 	Local  bool
+	DryRun bool
 
 	OutputFormat string
 }
@@ -91,6 +91,7 @@ func NewCmdPatch(f cmdutil.Factory, out io.Writer) *cobra.Command {
 		Example: patchExample,
 		Run: func(cmd *cobra.Command, args []string) {
 			options.OutputFormat = cmdutil.GetFlagString(cmd, "output")
+			options.DryRun = cmdutil.GetFlagBool(cmd, "dry-run")
 			err := RunPatch(f, out, cmd, args, options)
 			cmdutil.CheckErr(err)
 		},
@@ -102,6 +103,7 @@ func NewCmdPatch(f cmdutil.Factory, out io.Writer) *cobra.Command {
 	cmd.Flags().String("type", "strategic", fmt.Sprintf("The type of patch being provided; one of %v", sets.StringKeySet(patchTypes).List()))
 	cmdutil.AddPrinterFlags(cmd)
 	cmdutil.AddRecordFlag(cmd)
+	cmdutil.AddDryRunFlag(cmd)
 	cmdutil.AddInclude3rdPartyFlags(cmd)
 
 	usage := "identifying the resource to update"
@@ -168,9 +170,7 @@ func RunPatch(f cmdutil.Factory, out io.Writer, cmd *cobra.Command, args []strin
 			return err
 		}
 
-		if !options.Local {
+		if !options.Local && !options.DryRun {
-			dataChangedMsg := "not patched"
-			didPatch := false
 			helper := resource.NewHelper(client, mapping)
 			patchedObj, err := helper.Patch(namespace, name, patchType, patchBytes)
 			if err != nil {
@@ -191,18 +191,7 @@ func RunPatch(f cmdutil.Factory, out io.Writer, cmd *cobra.Command, args []strin
 			}
 			count++
 
-			oldData, err := json.Marshal(info.Object)
+			didPatch := !reflect.DeepEqual(info.Object, patchedObj)
-			if err != nil {
-				return err
-			}
-			newData, err := json.Marshal(patchedObj)
-			if err != nil {
-				return err
-			}
-			if !reflect.DeepEqual(oldData, newData) {
-				didPatch = true
-				dataChangedMsg = "patched"
-			}
 
 			// After computing whether we changed data, refresh the resource info with the resulting object
 			if err := info.Refresh(patchedObj, true); err != nil {
@@ -212,7 +201,7 @@ func RunPatch(f cmdutil.Factory, out io.Writer, cmd *cobra.Command, args []strin
 			if len(options.OutputFormat) > 0 && options.OutputFormat != "name" {
 				return cmdutil.PrintObject(cmd, info.Object, out)
 			}
-			cmdutil.PrintSuccess(options.OutputFormat == "name", out, info.Object, false, dataChangedMsg)
+			cmdutil.PrintSuccess(options.OutputFormat == "name", out, info.Object, false, patchOperation(didPatch))
 
 			// if object was not successfully patched, exit with error code 1
 			if !didPatch {
@@ -239,14 +228,24 @@ func RunPatch(f cmdutil.Factory, out io.Writer, cmd *cobra.Command, args []strin
 			return err
 		}
 
+		didPatch := !reflect.DeepEqual(info.Object, targetObj)
+
 		// TODO: if we ever want to go generic, this allows a clean -o yaml without trying to print columns or anything
 		// rawExtension := &runtime.Unknown{
 		//	Raw: originalPatchedObjJS,
 		// }
+		if didPatch {
 			if err := info.Refresh(targetObj, true); err != nil {
 				return err
 			}
+		}
+
+		if len(options.OutputFormat) > 0 && options.OutputFormat != "name" {
 			return cmdutil.PrintObject(cmd, info.Object, out)
+		}
+
+		cmdutil.PrintSuccess(options.OutputFormat == "name", out, info.Object, options.DryRun, patchOperation(didPatch))
+		return nil
 	})
 	if err != nil {
 		return err
@@ -282,3 +281,10 @@ func getPatchedJSON(patchType types.PatchType, originalJS, patchJS []byte, gvk s
 		return nil, fmt.Errorf("unknown Content-Type header for patch: %v", patchType)
 	}
 }
+
+func patchOperation(didPatch bool) string {
+	if didPatch {
+		return "patched"
+	}
+	return "not patched"
+}