Sort commands by their names

The slice of commands are sorted now automatically while Commands are called.
To turn off this feature, EnableCommandSorting variable is added.

command.go

@@ -21,6 +21,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	flag "github.com/spf13/pflag"
@@ -103,6 +104,8 @@ type Command struct {
 	commandsMaxUseLen         int
 	commandsMaxCommandPathLen int
 	commandsMaxNameLen        int
+	// is commands slice are sorted or not
+	commandsAreSorted bool
 
 	flagErrorBuf *bytes.Buffer
 
@@ -721,8 +724,20 @@ func (c *Command) ResetCommands() {
 	c.helpCommand = nil
 }
 
-//Commands returns a slice of child commands.
+// Sorts commands by their names
+type commandSorterByName []*Command
+
+func (c commandSorterByName) Len() int           { return len(c) }
+func (c commandSorterByName) Swap(i, j int)      { c[i], c[j] = c[j], c[i] }
+func (c commandSorterByName) Less(i, j int) bool { return c[i].Name() < c[j].Name() }
+
+// Commands returns a sorted slice of child commands.
 func (c *Command) Commands() []*Command {
+	// do not sort commands if it already sorted or sorting was disabled
+	if EnableCommandSorting && !c.commandsAreSorted{
+		sort.Sort(commandSorterByName(c.commands))
+		c.commandsAreSorted = true
+	}
 	return c.commands
 }
 
@@ -751,6 +766,7 @@ func (c *Command) AddCommand(cmds ...*Command) {
 			x.SetGlobalNormalizationFunc(c.globNormFunc)
 		}
 		c.commands = append(c.commands, x)
+		c.commandsAreSorted = false
 	}
 }