kn version command to list supported serving versions and APIs (#370)

Fixes #369

 - Replace `Dependencies:` with `Support:`
 - Add list of supported Serving versions kn can work with
 - Add list of supported Serving APIs kn can work with

 ```
 ✗ ./kn version
Version:      v20190816-local-e36089f-dirty
Build Date:   2019-08-16 13:08:26
Git Revision: e36089f
Support:
- Serving: v0.8.0  v0.7.1
- API(s):  v1alpha1

 ```

CHANGELOG.adoc

@@ -46,6 +46,9 @@
 | Support traffic splitting and tagging targets
 | https://github.com/knative/client/pull/345[#345]
 
+| 🎁
+| kn version command shows supported Serving and API versions
+| https://github.com/knative/client/pull/370[#370]
 
 |===
 

pkg/kn/commands/version.go

@@ -16,6 +16,7 @@ package commands
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/spf13/cobra"
 )
@@ -25,6 +26,18 @@ var BuildDate string
 var GitRevision string
 var ServingVersion string
 
+// VersionsAPIs hold the list of supported versions and APIs for component kn can work with
+type VersionsAPIs struct {
+	Versions, APIs []string
+}
+
+// update this var as we increase the serving version in go.mod
+var knServingDep = "v0.8.0"
+var supportMatrix = map[string]*VersionsAPIs{
+	knServingDep: {[]string{"v0.8.0", "v0.7.1"}, []string{"v1alpha1"}},
+}
+
+// NewVersionCommand implements 'kn version' command
 func NewVersionCommand(p *KnParams) *cobra.Command {
 	versionCmd := &cobra.Command{
 		Use:   "version",
@@ -33,8 +46,15 @@ func NewVersionCommand(p *KnParams) *cobra.Command {
 			fmt.Printf("Version:      %s\n", Version)
 			fmt.Printf("Build Date:   %s\n", BuildDate)
 			fmt.Printf("Git Revision: %s\n", GitRevision)
-			fmt.Printf("Dependencies:\n")
+			fmt.Printf("Support:\n")
-			fmt.Printf("- serving:    %s\n", ServingVersion)
+			if m, ok := supportMatrix[ServingVersion]; ok {
+				fmt.Printf("- Serving: %s\n", strings.Join(m.Versions, "  "))
+				fmt.Printf("- API(s):  %s\n", strings.Join(m.APIs, " "))
+			} else {
+				// ensure the go build works when we update,
+				// but version command tests fails to prevent shipping
+				fmt.Printf("- Serving: %s\n", ServingVersion)
+			}
 			return nil
 		},
 	}

pkg/kn/commands/version_test.go

@@ -27,21 +27,21 @@ type versionOutput struct {
 	Version      string
 	BuildDate    string
 	GitRevision  string
-	ServingVersion string
+	VersionsAPIs *VersionsAPIs
 }
 
 var versionOutputTemplate = `Version:      {{.Version}}
 Build Date:   {{.BuildDate}}
 Git Revision: {{.GitRevision}}
-Dependencies:
+Support:
-- serving:    {{.ServingVersion}}
+- Serving: {{index .VersionsAPIs.Versions 0}}  {{index .VersionsAPIs.Versions 1}}
+- API(s):  {{index .VersionsAPIs.APIs 0}}
 `
 
 const (
 	fakeVersion     = "fake-version"
 	fakeBuildDate   = "fake-build-date"
 	fakeGitRevision = "fake-git-revision"
-	fakeServingVersion = "fake-serving-version"
 )
 
 func TestVersion(t *testing.T) {
@@ -55,14 +55,14 @@ func TestVersion(t *testing.T) {
 		Version = fakeVersion
 		BuildDate = fakeBuildDate
 		GitRevision = fakeGitRevision
-		ServingVersion = fakeServingVersion
+		ServingVersion = knServingDep
 
 		expectedVersionOutput = genVersionOuput(t, versionOutputTemplate,
 			versionOutput{
-				Version:        fakeVersion,
+				fakeVersion,
-				BuildDate:      fakeBuildDate,
+				fakeBuildDate,
-				GitRevision:    fakeGitRevision,
+				fakeGitRevision,
-				ServingVersion: fakeServingVersion})
+				supportMatrix[ServingVersion]})
 
 		knParams = &KnParams{}
 		versionCmd = NewVersionCommand(knParams)
@@ -78,26 +78,27 @@ func TestVersion(t *testing.T) {
 		assert.Assert(t, versionCmd.RunE != nil)
 	})
 
-	t.Run("prints version, build date, git revision, and serving version string", func(t *testing.T) {
+	t.Run("prints version, build date, git revision, supported serving version and APIs", func(t *testing.T) {
 		setup()
 		CaptureStdout(t)
 		defer ReleaseStdout(t)
 
 		err := versionCmd.RunE(nil, []string{})
-		assert.Assert(t, err == nil)
+		assert.NilError(t, err)
 		assert.Equal(t, ReadStdout(t), expectedVersionOutput)
 	})
+
 }
 
 // Private
 
 func genVersionOuput(t *testing.T, templ string, vOutput versionOutput) string {
 	tmpl, err := template.New("versionOutput").Parse(versionOutputTemplate)
-	assert.Assert(t, err == nil)
+	assert.NilError(t, err)
 
 	buf := bytes.Buffer{}
 	err = tmpl.Execute(&buf, vOutput)
-	assert.Assert(t, err == nil)
+	assert.NilError(t, err)
 
 	return buf.String()
 }