closes #2130 new command flag ErrorOnUnknownSubcommand

command.go

@@ -44,6 +44,10 @@ type Group struct {
 	Title string
 }
 
+// ErrUnknownSubcommand is returned by Command.Execute() when the subcommand was not found.
+// Hereto, the ErrorOnUnknownSubcommand flag must be set true.
+var ErrUnknownSubcommand = errors.New("subcommand is unknown")
+
 // Command is just that, a command for your application.
 // E.g.  'go run ...' - 'run' is the command. Cobra requires
 // you to define the usage and description as part of your command
@@ -254,6 +258,17 @@ type Command struct {
 	// SuggestionsMinimumDistance defines minimum levenshtein distance to display suggestions.
 	// Must be > 0.
 	SuggestionsMinimumDistance int
+
+	// ErrorOnUnknownSubcommand controls the behavior of subcommand handling.
+	// When the flag is set true the behavior of Command.Execute() will change:
+	// If a sub-subcommand is not found ErrUnknownSubcommand will be returned on calling
+	// Command.Exec() instead of the old behavior where a nil error was sent.
+	// If the flag is false (default) the old behavior is performed.
+	// For this behavior the child subcommand must be nil.
+	// Example: in root/service/run - there would be an existing subcommand `run`
+	// in root/service/unknown - there would be an unknown subcommand `unknown` therefore returning an error
+	// `service` must have a nil Command.Run() function for this.
+	ErrorOnUnknownSubcommand bool
 }
 
 // Context returns underlying command context. If command was executed
@@ -924,9 +939,12 @@ func (c *Command) execute(a []string) (err error) {
 	}
 
 	if !c.Runnable() {
-		return flag.ErrHelp
+		if c.ErrorOnUnknownSubcommand {
+			return ErrUnknownSubcommand
+		} else {
+			return flag.ErrHelp
+		}
 	}
-
 	c.preRun()
 
 	defer c.postRun()

command_test.go

@@ -17,6 +17,7 @@ package cobra
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -174,6 +175,94 @@ func TestSubcommandExecuteC(t *testing.T) {
 	}
 }
 
+func TestSubcommandExecuteMissingSubcommand(t *testing.T) {
+	rootCmd := &Command{Use: "root", Run: emptyRun}
+	childCmd := &Command{Use: "child", Run: nil, ErrorOnUnknownSubcommand: false}
+	child2Cmd := &Command{Use: "child2", Run: emptyRun}
+	rootCmd.AddCommand(childCmd)
+	childCmd.AddCommand(child2Cmd)
+
+	// test existing command
+	c, output, err := executeCommandC(rootCmd, "child")
+	if !strings.HasPrefix(output, "Usage:") {
+		t.Errorf("Unexpected output: %v", output)
+	}
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if c.Name() != "child" {
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
+	}
+
+	// test existing sub command
+	c, output, err = executeCommandC(rootCmd, "child", "child2")
+	if output != "" {
+		t.Errorf("Unexpected output: %v", output)
+	}
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if c.Name() != "child2" {
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
+	}
+
+	// now test a command which does not exist, we will get no error, just "Usage:" is printed
+	c, output, err = executeCommandC(rootCmd, "child", "unknownChild")
+	if !strings.HasPrefix(output, "Usage:") {
+		t.Errorf("Expected: 'Usage: ...'\nGot:\n %q\n", output)
+	}
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if c.Name() != "child" {
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
+	}
+}
+
+func TestSubcommandExecuteMissingSubcommandWithErrorOnUnknownSubcommand(t *testing.T) {
+	rootCmd := &Command{Use: "root", Run: emptyRun}
+	childCmd := &Command{Use: "child", Run: nil, ErrorOnUnknownSubcommand: true}
+	child2Cmd := &Command{Use: "child2", Run: emptyRun}
+	rootCmd.AddCommand(childCmd)
+	childCmd.AddCommand(child2Cmd)
+
+	// test existing command
+	c, output, err := executeCommandC(rootCmd, "child")
+	if !strings.HasPrefix(output, "Error:") {
+		t.Errorf("Unexpected output: %v", output)
+	}
+	if !errors.Is(err, ErrUnknownSubcommand) {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if c.Name() != "child" {
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
+	}
+
+	// test existing sub command
+	c, output, err = executeCommandC(rootCmd, "child", "child2")
+	if output != "" {
+		t.Errorf("Unexpected output: %v", output)
+	}
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if c.Name() != "child2" {
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
+	}
+
+	// now test a command which does not exist, we expect an error because of the ErrorOnUnknownSubcommand flag
+	c, output, err = executeCommandC(rootCmd, "child", "unknownChild")
+	if !strings.HasPrefix(output, "Error:") {
+		t.Errorf("Unexpected output: %v", output)
+	}
+	if !errors.Is(err, ErrUnknownSubcommand) {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if c.Name() != "child" {
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
+	}
+}
+
 func TestExecuteContext(t *testing.T) {
 	ctx := context.TODO()