New `Hide` variable for all Flags

This is a way to provide hidden flags for app, command and subcommands

For example:

  --generate-bash-completion global flag shouldn't be printed along
  with other flags as it might generally confuse people into thinking
  that 'generate' in-fact would generate a bash completion file for them
  to be used along with their app.

Also in general one would want to hide some flags for their apps.

flag.go

@@ -13,6 +13,7 @@ import (
 // This flag enables bash-completion for all commands and subcommands
 var BashCompletionFlag = BoolFlag{
 	Name: "generate-bash-completion",
+	Hide: true,
 }
 
 // This flag prints the version for the application
@@ -37,6 +38,7 @@ type Flag interface {
 	// Apply Flag settings to the given flag set
 	Apply(*flag.FlagSet)
 	GetName() string
+	isNotHidden() bool
 }
 
 func flagSet(name string, flags []Flag) *flag.FlagSet {
@@ -68,6 +70,7 @@ type GenericFlag struct {
 	Value  Generic
 	Usage  string
 	EnvVar string
+	Hide   bool
 }
 
 // String returns the string representation of the generic flag to display the
@@ -112,6 +115,10 @@ func (f GenericFlag) GetName() string {
 	return f.Name
 }
 
+func (f GenericFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // StringSlice is an opaque type for []string to satisfy flag.Value
 type StringSlice []string
 
@@ -138,6 +145,7 @@ type StringSliceFlag struct {
 	Value  *StringSlice
 	Usage  string
 	EnvVar string
+	Hide   bool
 }
 
 // String returns the usage
@@ -177,6 +185,10 @@ func (f StringSliceFlag) GetName() string {
 	return f.Name
 }
 
+func (f StringSliceFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // StringSlice is an opaque type for []int to satisfy flag.Value
 type IntSlice []int
 
@@ -208,6 +220,7 @@ type IntSliceFlag struct {
 	Value  *IntSlice
 	Usage  string
 	EnvVar string
+	Hide   bool
 }
 
 // String returns the usage
@@ -250,12 +263,17 @@ func (f IntSliceFlag) GetName() string {
 	return f.Name
 }
 
+func (f IntSliceFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // BoolFlag is a switch that defaults to false
 type BoolFlag struct {
 	Name        string
 	Usage       string
 	EnvVar      string
 	Destination *bool
+	Hide        bool
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -293,6 +311,10 @@ func (f BoolFlag) GetName() string {
 	return f.Name
 }
 
+func (f BoolFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // BoolTFlag this represents a boolean flag that is true by default, but can
 // still be set to false by --some-flag=false
 type BoolTFlag struct {
@@ -300,6 +322,7 @@ type BoolTFlag struct {
 	Usage       string
 	EnvVar      string
 	Destination *bool
+	Hide        bool
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -337,6 +360,10 @@ func (f BoolTFlag) GetName() string {
 	return f.Name
 }
 
+func (f BoolTFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // StringFlag represents a flag that takes as string value
 type StringFlag struct {
 	Name        string
@@ -344,6 +371,7 @@ type StringFlag struct {
 	Usage       string
 	EnvVar      string
 	Destination *string
+	Hide        bool
 }
 
 // String returns the usage
@@ -385,6 +413,10 @@ func (f StringFlag) GetName() string {
 	return f.Name
 }
 
+func (f StringFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // IntFlag is a flag that takes an integer
 // Errors if the value provided cannot be parsed
 type IntFlag struct {
@@ -393,6 +425,7 @@ type IntFlag struct {
 	Usage       string
 	EnvVar      string
 	Destination *int
+	Hide        bool
 }
 
 // String returns the usage
@@ -429,6 +462,10 @@ func (f IntFlag) GetName() string {
 	return f.Name
 }
 
+func (f IntFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // DurationFlag is a flag that takes a duration specified in Go's duration
 // format: https://golang.org/pkg/time/#ParseDuration
 type DurationFlag struct {
@@ -437,6 +474,7 @@ type DurationFlag struct {
 	Usage       string
 	EnvVar      string
 	Destination *time.Duration
+	Hide        bool
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -473,6 +511,10 @@ func (f DurationFlag) GetName() string {
 	return f.Name
 }
 
+func (f DurationFlag) isNotHidden() bool {
+	return !f.Hide
+}
+
 // Float64Flag is a flag that takes an float value
 // Errors if the value provided cannot be parsed
 type Float64Flag struct {
@@ -481,6 +523,7 @@ type Float64Flag struct {
 	Usage       string
 	EnvVar      string
 	Destination *float64
+	Hide        bool
 }
 
 // String returns the usage
@@ -516,6 +559,10 @@ func (f Float64Flag) GetName() string {
 	return f.Name
 }
 
+func (f Float64Flag) isNotHidden() bool {
+	return !f.Hide
+}
+
 func prefixFor(name string) (prefix string) {
 	if len(name) == 1 {
 		prefix = "-"

help.go

@@ -114,7 +114,15 @@ var HelpPrinter helpPrinter = printHelp
 var VersionPrinter = printVersion
 
 func ShowAppHelp(c *Context) {
-	HelpPrinter(c.App.Writer, AppHelpTemplate, c.App)
+	// Make a copy of c.App context
+	app := *c.App
+	app.Flags = make([]Flag, 0)
+	for _, flag := range c.App.Flags {
+		if flag.isNotHidden() {
+			app.Flags = append(app.Flags, flag)
+		}
+	}
+	HelpPrinter(c.App.Writer, AppHelpTemplate, app)
 }
 
 // Prints the list of subcommands as the default app completion method
@@ -130,13 +138,29 @@ func DefaultAppComplete(c *Context) {
 func ShowCommandHelp(ctx *Context, command string) {
 	// show the subcommand help for a command with subcommands
 	if command == "" {
-		HelpPrinter(ctx.App.Writer, SubcommandHelpTemplate, ctx.App)
+		// Make a copy of c.App context
+		app := *c.App
+		app.Flags = make([]Flag, 0)
+		for _, flag := range c.App.Flags {
+			if flag.isNotHidden() {
+				app.Flags = append(app.Flags, flag)
+			}
+		}
+		HelpPrinter(ctx.App.Writer, SubcommandHelpTemplate, app)
 		return
 	}
 
 	for _, c := range ctx.App.Commands {
 		if c.HasName(command) {
-			HelpPrinter(ctx.App.Writer, CommandHelpTemplate, c)
+			// Make a copy of command context
+			c0 := c
+			c0.Flags = make([]Flag, 0)
+			for _, flag := range c.Flags {
+				if flag.isNotHidden() {
+					c0.Flags = append(c0.Flags, flag)
+				}
+			}
+			HelpPrinter(ctx.App.Writer, CommandHelpTemplate, c0)
 			return
 		}
 	}