Add machine readable output for trigger

CHANGELOG.adoc

@@ -20,16 +20,18 @@
 | 🐛
 | Embed the namespace in request body while creating channels
 | https://github.com/knative/client/pull/1117[#1117]
-|===
 
 | 🎁
 | Add "url" output format to return broker url in broker describe and channel url in channel describe
 | https://github.com/knative/client/pull/1118[#1118]
-|===
 
 | 🎁
 | Add machine readable output (-o flag) to kn broker describe
 | https://github.com/knative/client/pull/1124[#1124]
+
+| 🎁
+| Add machine readable output (-o flag) to kn trigger describe
+| https://github.com/knative/client/pull/1121[#1121]
 |===
 
 ### v0.19.0 (2020-11-11)

docs/cmd/kn_trigger_describe.md

@@ -16,14 +16,20 @@ kn trigger describe NAME
 
   # Describe a trigger with name 'my-trigger'
   kn trigger describe my-trigger
+
+  # Describe a trigger 'my-trigger' in YAML format
+  kn trigger describe my-trigger -o yaml
 ```
 
 ### Options
 
 ```
-  -h, --help               help for describe
-  -n, --namespace string   Specify the namespace to operate in.
-  -v, --verbose            More output.
+      --allow-missing-template-keys   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. (default true)
+  -h, --help                          help for describe
+  -n, --namespace string              Specify the namespace to operate in.
+  -o, --output string                 Output format. One of: json|yaml|name|go-template|go-template-file|template|templatefile|jsonpath|jsonpath-file.
+      --template string               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].
+  -v, --verbose                       More output.
 ```
 
 ### Options inherited from parent commands

pkg/eventing/v1beta1/client.go

@@ -97,6 +97,10 @@ func (c *knEventingClient) GetTrigger(name string) (*v1beta1.Trigger, error) {
 	if err != nil {
 		return nil, kn_errors.GetError(err)
 	}
+	err = updateEventingGVK(trigger)
+	if err != nil {
+		return nil, err
+	}
 	return trigger, nil
 }
 

pkg/kn/commands/trigger/describe.go

@@ -16,6 +16,10 @@ package trigger
 
 import (
 	"errors"
+	"fmt"
+	"strings"
+
+	"k8s.io/cli-runtime/pkg/genericclioptions"
 
 	"github.com/spf13/cobra"
 
@@ -26,15 +30,23 @@ import (
 	"knative.dev/client/pkg/printers"
 )
 
+var describeExample = `
+  # Describe a trigger with name 'my-trigger'
+  kn trigger describe my-trigger
+
+  # Describe a trigger 'my-trigger' in YAML format
+  kn trigger describe my-trigger -o yaml`
+
 // NewTriggerDescribeCommand returns a new command for describe a trigger
 func NewTriggerDescribeCommand(p *commands.KnParams) *cobra.Command {
 
-	triggerDescribe := &cobra.Command{
-		Use:   "describe NAME",
-		Short: "Show details of a trigger",
-		Example: `
-  # Describe a trigger with name 'my-trigger'
-  kn trigger describe my-trigger`,
+	// For machine readable output
+	machineReadablePrintFlags := genericclioptions.NewPrintFlags("")
+
+	command := &cobra.Command{
+		Use:     "describe NAME",
+		Short:   "Show details of a trigger",
+		Example: describeExample,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if len(args) != 1 {
 				return errors.New("'kn trigger describe' requires name of the trigger as single argument")
@@ -59,6 +71,16 @@ func NewTriggerDescribeCommand(p *commands.KnParams) *cobra.Command {
 			}
 
 			out := cmd.OutOrStdout()
+
+			// Print out machine readable output if requested
+			if machineReadablePrintFlags.OutputFlagSpecified() {
+				printer, err := machineReadablePrintFlags.ToPrinter()
+				if err != nil {
+					return err
+				}
+				return printer.PrintObj(trigger, out)
+			}
+
 			dw := printers.NewPrefixWriter(out)
 
 			printDetails, err := cmd.Flags().GetBool("verbose")
@@ -88,11 +110,12 @@ func NewTriggerDescribeCommand(p *commands.KnParams) *cobra.Command {
 			return nil
 		},
 	}
-	flags := triggerDescribe.Flags()
+	flags := command.Flags()
 	commands.AddNamespaceFlags(flags, false)
 	flags.BoolP("verbose", "v", false, "More output.")
-
-	return triggerDescribe
+	machineReadablePrintFlags.AddFlags(command)
+	command.Flag("output").Usage = fmt.Sprintf("Output format. One of: %s.", strings.Join(machineReadablePrintFlags.AllowedFormats(), "|"))
+	return command
 }
 
 func writeTrigger(dw printers.PrefixWriter, trigger *v1beta1.Trigger, printDetails bool) {

pkg/kn/commands/trigger/describe_test.go

@@ -81,9 +81,26 @@ func TestDescribeTriggerWithSinkURI(t *testing.T) {
 	recorder.Validate()
 }
 
+func TestDescribeTriggerMachineReadable(t *testing.T) {
+	client := clientv1beta1.NewMockKnEventingClient(t, "mynamespace")
+
+	recorder := client.Recorder()
+	recorder.GetTrigger("testtrigger", getTriggerSinkRef(), nil)
+
+	output, err := executeTriggerCommand(client, nil, "describe", "testtrigger", "-o", "yaml")
+	assert.NilError(t, err)
+	assert.Assert(t, util.ContainsAll(output, "kind: Trigger", "spec:", "status:", "metadata:"))
+
+	// Validate that all recorded API methods have been called
+	recorder.Validate()
+}
+
 func getTriggerSinkRef() *v1beta1.Trigger {
 	return &v1beta1.Trigger{
-		TypeMeta: v1.TypeMeta{},
+		TypeMeta: v1.TypeMeta{
+			Kind:       "Trigger",
+			APIVersion: "eventing.knative.dev/v1beta1",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      "testtrigger",
 			Namespace: "default",
@@ -110,7 +127,10 @@ func getTriggerSinkRef() *v1beta1.Trigger {
 
 func getTriggerSinkURI() *v1beta1.Trigger {
 	return &v1beta1.Trigger{
-		TypeMeta: v1.TypeMeta{},
+		TypeMeta: v1.TypeMeta{
+			Kind:       "Trigger",
+			APIVersion: "eventing.knative.dev/v1beta1",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      "testtrigger",
 			Namespace: "default",