Check for group presence after full initialization

Fixes #1831

By moving the check for help group existence to "ExecuteC()" we no
longer need groups to be added before AddCommand() is called.  This
provides more flexibility to developers and works better with the use
of "init()" for command creation.

Signed-off-by: Marc Khouzam <marc.khouzam@gmail.com>

command.go

@@ -998,6 +998,10 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 	// initialize completion at the last point to allow for user overriding
 	c.InitDefaultCompletionCmd()
 
+	// Now that all commands have been created, let's make sure all	 groups
+	// are properly created also
+	c.checkCommandGroups()
+
 	args := c.args
 
 	// Workaround FAIL with "go test -v" or "cobra.test -test.v", see #155
@@ -1092,6 +1096,19 @@ func (c *Command) ValidateRequiredFlags() error {
 	return nil
 }
 
+// checkCommandGroups checks if a command has been added to a group that does not exists.
+// If so, we panic because it indicates a coding error that should be corrected.
+func (c *Command) checkCommandGroups() {
+	for _, sub := range c.commands {
+		// if Group is not defined let the developer know right away
+		if sub.GroupID != "" && !c.ContainsGroup(sub.GroupID) {
+			panic(fmt.Sprintf("group id '%s' is not defined for subcommand '%s'", sub.GroupID, sub.CommandPath()))
+		}
+
+		sub.checkCommandGroups()
+	}
+}
+
 // InitDefaultHelpFlag adds default help flag to c.
 // It is called automatically by executing the c or by calling help and usage.
 // If c already has help flag, it will do nothing.
@@ -1218,10 +1235,6 @@ func (c *Command) AddCommand(cmds ...*Command) {
 			panic("Command can't be a child of itself")
 		}
 		cmds[i].parent = c
-		// if Group is not defined let the developer know right away
-		if x.GroupID != "" && !c.ContainsGroup(x.GroupID) {
-			panic(fmt.Sprintf("Group id '%s' is not defined for subcommand '%s'", x.GroupID, cmds[i].CommandPath()))
-		}
 		// update max lengths
 		usageLen := len(x.Use)
 		if usageLen > c.commandsMaxUseLen {

command_test.go

@@ -1862,6 +1862,84 @@ func TestAddGroup(t *testing.T) {
 	checkStringContains(t, output, "\nTest group\n  cmd")
 }
 
+func TestMissingGroupFirstLevel(t *testing.T) {
+	var rootCmd = &Command{Use: "root", Short: "test", Run: emptyRun}
+
+	rootCmd.AddGroup(&Group{ID: "group", Title: "Test group"})
+	// Use the wrong group ID
+	rootCmd.AddCommand(&Command{Use: "cmd", GroupID: "wrong", Run: emptyRun})
+
+	defer func() {
+		if recover() == nil {
+			t.Errorf("The code should have panicked due to a missing group")
+		}
+	}()
+	_, err := executeCommand(rootCmd, "--help")
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+}
+
+func TestMissingGroupNestedLevel(t *testing.T) {
+	var rootCmd = &Command{Use: "root", Short: "test", Run: emptyRun}
+	var childCmd = &Command{Use: "child", Run: emptyRun}
+	rootCmd.AddCommand(childCmd)
+
+	childCmd.AddGroup(&Group{ID: "group", Title: "Test group"})
+	// Use the wrong group ID
+	childCmd.AddCommand(&Command{Use: "cmd", GroupID: "wrong", Run: emptyRun})
+
+	defer func() {
+		if recover() == nil {
+			t.Errorf("The code should have panicked due to a missing group")
+		}
+	}()
+	_, err := executeCommand(rootCmd, "child", "--help")
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+}
+
+func TestMissingGroupForHelp(t *testing.T) {
+	var rootCmd = &Command{Use: "root", Short: "test", Run: emptyRun}
+	var childCmd = &Command{Use: "child", Run: emptyRun}
+	rootCmd.AddCommand(childCmd)
+
+	rootCmd.AddGroup(&Group{ID: "group", Title: "Test group"})
+	// Use the wrong group ID
+	rootCmd.SetHelpCommandGroupID("wrong")
+
+	defer func() {
+		if recover() == nil {
+			t.Errorf("The code should have panicked due to a missing group")
+		}
+	}()
+	_, err := executeCommand(rootCmd, "--help")
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+}
+
+func TestMissingGroupForCompletion(t *testing.T) {
+	var rootCmd = &Command{Use: "root", Short: "test", Run: emptyRun}
+	var childCmd = &Command{Use: "child", Run: emptyRun}
+	rootCmd.AddCommand(childCmd)
+
+	rootCmd.AddGroup(&Group{ID: "group", Title: "Test group"})
+	// Use the wrong group ID
+	rootCmd.SetCompletionCommandGroupID("wrong")
+
+	defer func() {
+		if recover() == nil {
+			t.Errorf("The code should have panicked due to a missing group")
+		}
+	}()
+	_, err := executeCommand(rootCmd, "--help")
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+}
+
 func TestSetOutput(t *testing.T) {
 	c := &Command{}
 	c.SetOutput(nil)