fixes(#814) allow plugins to extend the 'source' command group

CHANGELOG.adoc

@@ -30,6 +30,10 @@
 | Check DeleteTimestamp before updating resource
 | https://github.com/knative/client/pull/805[#805]
 
+| 🎁
+| Allow plugins to extend fixed list of command groups, currently `source`
+| https://github.com/knative/client/pull/818[#818]
+
 | 🎁
 | Add `-a` flag as an alias for `--annotation`
 | https://github.com/knative/client/pull/782[#782]

pkg/kn/commands/plugin/list_test.go

@@ -71,7 +71,6 @@ func (ctx *testContext) createTestPluginWithPath(pluginName string, fileMode os.
 }
 
 func TestPluginList(t *testing.T) {
-
 	setup := func(t *testing.T) *testContext {
 		knParams := &commands.KnParams{}
 		pluginCmd := NewPluginCommand(knParams)
@@ -159,7 +158,6 @@ func TestPluginList(t *testing.T) {
 				})
 
 				t.Run("with plugins with same name", func(t *testing.T) {
-
 					t.Run("warns user about second (in $PATH) plugin shadowing first", func(t *testing.T) {
 						ctx := setup(t)
 						defer ctx.cleanup()
@@ -201,6 +199,24 @@ func TestPluginList(t *testing.T) {
 						assert.ErrorContains(t, err, "overwrite", "built-in")
 						assert.Assert(t, util.ContainsAll(ctx.output(), "ERROR", "overwrite", "built-in"))
 					})
+
+					t.Run("allows plugin under the `source` command group", func(t *testing.T) {
+						ctx := setup(t)
+						defer ctx.cleanup()
+
+						sourceCmd := &cobra.Command{
+							Use: "source",
+						}
+						ctx.rootCmd.AddCommand(sourceCmd)
+						defer ctx.rootCmd.RemoveCommand(sourceCmd)
+
+						err := ctx.createTestPlugin("kn-source-fake", FileModeExecutable, true)
+						assert.NilError(t, err)
+
+						err = ctx.execute("plugin", "list", "--lookup-plugins=true")
+						assert.NilError(t, err)
+					})
+
 				})
 			})
 		})

pkg/kn/commands/plugin/plugin.go

@@ -52,3 +52,20 @@ func BindPluginsFlagToViper(cmd *cobra.Command) {
 	viper.SetDefault("plugins-dir", commands.Cfg.DefaultPluginDir)
 	viper.SetDefault("lookup-plugins", false)
 }
+
+// AllowedExtensibleCommandGroups the list of command groups that can be
+// extended with plugins, e.g., a plugin named `kn-source-kafka` for Kafka
+// event sources is allowed. This is defined as a fixed [...]string since
+// cannot defined Golang []string constants
+var AllowedExtensibleCommandGroups = [...]string{"source"}
+
+// InAllowedExtensibleCommandGroups checks that the name is in the list of allowed
+// extensible command groups
+func InAllowedExtensibleCommandGroups(name string) bool {
+	for _, groupName := range AllowedExtensibleCommandGroups {
+		if name == groupName {
+			return true
+		}
+	}
+	return false
+}

pkg/kn/commands/plugin/plugin_test.go

@@ -72,3 +72,13 @@ func TestNewPluginCommand(t *testing.T) {
 		assert.Assert(t, pluginCmd.Args == nil)
 	})
 }
+
+func TestInAllowedExtensibleCommandGroups(t *testing.T) {
+	isExtensibleCommand := InAllowedExtensibleCommandGroups("fake")
+	assert.Assert(t, isExtensibleCommand == false)
+
+	for _, name := range AllowedExtensibleCommandGroups {
+		isExtensibleCommand = InAllowedExtensibleCommandGroups(name)
+		assert.Assert(t, isExtensibleCommand == true)
+	}
+}

pkg/kn/commands/plugin/verifier.go

@@ -110,7 +110,9 @@ func (v *pluginVerifier) addErrorIfOverwritingExistingCommand(eaw errorsAndWarni
 	for _, c := range [][]string{cmds, convertUnderscoresToDashes(cmds)} {
 		cmd, _, err := v.root.Find(c)
 		if err == nil {
-			overwrittenCommands[cmd.CommandPath()] = true
+			if !InAllowedExtensibleCommandGroups(cmd.Name()) {
+				overwrittenCommands[cmd.CommandPath()] = true
+			}
 		}
 	}
 	for command := range overwrittenCommands {

pkg/kn/commands/plugin/verifier_test.go

@@ -33,7 +33,6 @@ import (
 )
 
 func TestPluginVerifier(t *testing.T) {
-
 	var (
 		pluginPath string
 		rootCmd    *cobra.Command
@@ -143,6 +142,20 @@ func TestPluginVerifier(t *testing.T) {
 				assert.Assert(t, util.ContainsAll(eaw.errors[0], "overwrite", "kn-plugin"))
 			})
 		})
+
+		t.Run("when kn plugin in path overwrites 'source' command (which is allowed)", func(t *testing.T) {
+			setup(t)
+			defer cleanup(t)
+			var overwritingPluginPath = CreateTestPlugin(t, "kn-source-test", KnTestPluginScript, FileModeExecutable)
+			defer DeleteTestPlugin(t, overwritingPluginPath)
+
+			t.Run("runs successfully", func(t *testing.T) {
+				eaw := errorsAndWarnings{}
+				eaw = verifier.verify(eaw, overwritingPluginPath)
+				assert.Assert(t, len(eaw.errors) == 0)
+				assert.Assert(t, len(eaw.warnings) == 0)
+			})
+		})
 	})
 }
 

pkg/kn/core/root.go

@@ -81,7 +81,7 @@ func NewDefaultKnCommandWithArgs(rootCmd *cobra.Command,
 		// only look for suitable extension executables if
 		// the specified command does not already exist
 		foundCmd, innerArgs, err := rootCmd.Find(cmdPathPieces)
-		if err != nil {
+		if err != nil || plugin.InAllowedExtensibleCommandGroups(foundCmd.Name()) {
 			err := plugin.HandlePluginCommand(pluginHandler, cmdPathPieces)
 			if err != nil {
 				fmt.Fprintf(rootCmd.OutOrStderr(), "Error: unknown command '%s' \nRun 'kn --help' for usage.\n", args[1])