Backward compatibility

An error is only thrown if there are arguments to a valid command.
Without any arguments the help is printed as before.
An invalid subcommand will return an error.

cobra.go

@@ -68,7 +68,7 @@ var EnableTraverseRunHooks = defaultTraverseRunHooks
 
 // EnableErrorOnUnknownSubcommand 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
+// If a sub-subcommand is not found an error 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.

command.go

@@ -44,10 +44,6 @@ 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
@@ -927,9 +923,14 @@ func (c *Command) execute(a []string) (err error) {
 		}
 	}
 
+	argWoFlags := c.Flags().Args()
+	if c.DisableFlagParsing {
+		argWoFlags = a
+	}
+
 	if !c.Runnable() {
-		if EnableErrorOnUnknownSubcommand {
+		if EnableErrorOnUnknownSubcommand && len(argWoFlags) > 0 {
-			return ErrUnknownSubcommand
+			return fmt.Errorf("unknown command %q for %q%s", argWoFlags[0], c.CommandPath(), c.findSuggestions(argWoFlags[0]))
 		} else {
 			return flag.ErrHelp
 		}
@@ -938,11 +939,6 @@ func (c *Command) execute(a []string) (err error) {
 
 	defer c.postRun()
 
-	argWoFlags := c.Flags().Args()
-	if c.DisableFlagParsing {
-		argWoFlags = a
-	}
-
 	if err := c.ValidateArgs(argWoFlags); err != nil {
 		return err
 	}

command_test.go

@@ -17,7 +17,6 @@ package cobra
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -224,7 +223,8 @@ func TestSubcommandExecuteMissingSubcommand(t *testing.T) {
 }
 
 func TestSubcommandExecuteMissingSubcommandWithErrorOnUnknownSubcommand(t *testing.T) {
-	rootCmd := &Command{Use: "root", Run: emptyRun}
+	const rootName = "root"
+	rootCmd := &Command{Use: rootName, Run: emptyRun}
 	const childName = "child"
 	const grandchildName = "grandchild"
 	EnableErrorOnUnknownSubcommand = true
@@ -236,10 +236,10 @@ func TestSubcommandExecuteMissingSubcommandWithErrorOnUnknownSubcommand(t *testi
 
 	// test existing command
 	c, output, err := executeCommandC(rootCmd, childName)
-	if !strings.HasPrefix(output, "Error:") {
+	if strings.HasPrefix(output, "Error:") {
 		t.Errorf("Unexpected output: %v", output)
 	}
-	if !errors.Is(err, ErrUnknownSubcommand) {
+	if err != nil {
 		t.Errorf("Unexpected error: %v", err)
 	}
 	if c.Name() != childName {
@@ -258,12 +258,30 @@ func TestSubcommandExecuteMissingSubcommandWithErrorOnUnknownSubcommand(t *testi
 		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
+	// test a child command which does not exist, we expect an error because of the ErrorOnUnknownSubcommand flag
-	c, output, err = executeCommandC(rootCmd, childName, "unknownChild")
+	c, output, err = executeCommandC(rootCmd, "unknownChild")
 	if !strings.HasPrefix(output, "Error:") {
 		t.Errorf("Unexpected output: %v", output)
 	}
-	if !errors.Is(err, ErrUnknownSubcommand) {
+	if err == nil {
+		t.Error("Expected error")
+	}
+	if err != nil && !strings.HasPrefix(err.Error(), "unknown command") {
+		t.Errorf("Unexpected error: %v", err)
+	}
+	if c.Name() != rootName {
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
+	}
+
+	// test a grandchild command which does not exist, we expect an error because of the ErrorOnUnknownSubcommand flag
+	c, output, err = executeCommandC(rootCmd, childName, "unknownGrandChild")
+	if !strings.HasPrefix(output, "Error:") {
+		t.Errorf("Unexpected output: %v", output)
+	}
+	if err == nil {
+		t.Error("Expected error")
+	}
+	if err != nil && !strings.HasPrefix(err.Error(), "unknown command") {
 		t.Errorf("Unexpected error: %v", err)
 	}
 	if c.Name() != childName {