feat: flag action

app.go

@@ -305,6 +305,10 @@ func (a *App) RunContext(ctx context.Context, arguments []string) (err error) {
 		}
 	}
 
+	if err = runFlagActions(cCtx, a.Flags); err != nil {
+		return err
+	}
+
 	args := cCtx.Args()
 	if args.Present() {
 		name := args.First()
@@ -426,6 +430,10 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 		}
 	}
 
+	if err = runFlagActions(cCtx, a.Flags); err != nil {
+		return err
+	}
+
 	args := cCtx.Args()
 	if args.Present() {
 		name := args.First()
@@ -506,6 +514,24 @@ func (a *App) handleExitCoder(cCtx *Context, err error) {
 	}
 }
 
+func runFlagActions(c *Context, fs []Flag) error {
+	for _, f := range fs {
+		isSet := false
+		for _, name := range f.Names() {
+			if c.IsSet(name) {
+				isSet = true
+				break
+			}
+		}
+		if isSet {
+			if err := f.RunAction(c); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 // Author represents someone who has contributed to a cli project.
 type Author struct {
 	Name  string // The Authors name

app_test.go

@@ -2068,6 +2068,10 @@ func (c *customBoolFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+func (c *customBoolFlag) RunAction(*Context) error {
+	return nil
+}
+
 func (c *customBoolFlag) IsSet() bool {
 	return false
 }
@@ -2287,3 +2291,66 @@ func TestSetupInitializesOnlyNilWriters(t *testing.T) {
 		t.Errorf("expected a.Writer to be os.Stdout")
 	}
 }
+
+func TestFlagAction(t *testing.T) {
+	r := []string{}
+	actionFunc := func(c *Context, s string) error {
+		r = append(r, s)
+		return nil
+	}
+
+	app := &App{
+		Name:   "command",
+		Writer: io.Discard,
+		Flags:  []Flag{&StringFlag{Name: "flag", Action: actionFunc}},
+		Commands: []*Command{
+			{
+				Name:  "command1",
+				Flags: []Flag{&StringFlag{Name: "flag1", Aliases: []string{"f1"}, Action: actionFunc}},
+				Subcommands: []*Command{
+					{
+						Name:  "command2",
+						Flags: []Flag{&StringFlag{Name: "flag2", Action: actionFunc}},
+					},
+				},
+			},
+		},
+	}
+
+	tests := []struct {
+		args []string
+		exp  []string
+	}{
+		{
+			args: []string{"command", "--flag=f"},
+			exp:  []string{"f"},
+		},
+		{
+			args: []string{"command", "command1", "-f1=f1", "command2"},
+			exp:  []string{"f1"},
+		},
+		{
+			args: []string{"command", "command1", "-f1=f1", "command2", "--flag2=f2"},
+			exp:  []string{"f1", "f2"},
+		},
+		{
+			args: []string{"command", "--flag=f", "command1", "-flag1=f1"},
+			exp:  []string{"f", "f1"},
+		},
+		{
+			args: []string{"command", "--flag=f", "command1", "-f1=f1"},
+			exp:  []string{"f", "f1"},
+		},
+		{
+			args: []string{"command", "--flag=f", "command1", "-f1=f1", "command2", "--flag2=f2"},
+			exp:  []string{"f", "f1", "f2"},
+		},
+	}
+
+	for _, test := range tests {
+		r = []string{}
+		err := app.Run(test.args)
+		expect(t, err, nil)
+		expect(t, r, test.exp)
+	}
+}

command.go

@@ -155,6 +155,10 @@ func (c *Command) Run(ctx *Context) (err error) {
 		}
 	}
 
+	if err = runFlagActions(cCtx, c.Flags); err != nil {
+		return err
+	}
+
 	if c.Action == nil {
 		c.Action = helpSubcommand.Action
 	}

flag.go

@@ -93,6 +93,7 @@ type Flag interface {
 	Apply(*flag.FlagSet) error
 	Names() []string
 	IsSet() bool
+	RunAction(*Context) error
 }
 
 // RequiredFlag is an interface that allows us to mark flags as required

flag_bool.go

@@ -19,6 +19,7 @@ type BoolFlag struct {
 	DefaultText string
 	Destination *bool
 	HasBeenSet  bool
+	Action      func(*Context, bool) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -76,6 +77,15 @@ func (f *BoolFlag) GetEnvVars() []string {
 	return f.EnvVars
 }
 
+// RunAction executes flag action if set
+func (f *BoolFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Bool(f.Name))
+	}
+
+	return nil
+}
+
 // Apply populates the flag given the flag set and environment
 func (f *BoolFlag) Apply(set *flag.FlagSet) error {
 	if val, ok := flagFromEnvOrFile(f.EnvVars, f.FilePath); ok {

flag_duration.go

@@ -19,6 +19,7 @@ type DurationFlag struct {
 	DefaultText string
 	Destination *time.Duration
 	HasBeenSet  bool
+	Action      func(*Context, time.Duration) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -101,6 +102,15 @@ func (f *DurationFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *DurationFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Duration(f.Name))
+	}
+
+	return nil
+}
+
 // Duration looks up the value of a local DurationFlag, returns
 // 0 if not found
 func (cCtx *Context) Duration(name string) time.Duration {

flag_float64.go

@@ -19,6 +19,7 @@ type Float64Flag struct {
 	DefaultText string
 	Destination *float64
 	HasBeenSet  bool
+	Action      func(*Context, float64) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -101,6 +102,15 @@ func (f *Float64Flag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *Float64Flag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Float64(f.Name))
+	}
+
+	return nil
+}
+
 // Float64 looks up the value of a local Float64Flag, returns
 // 0 if not found
 func (cCtx *Context) Float64(name string) float64 {

flag_float64_slice.go

@@ -87,6 +87,7 @@ type Float64SliceFlag struct {
 	Value       *Float64Slice
 	DefaultText string
 	HasBeenSet  bool
+	Action      func(*Context, []float64) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -177,6 +178,15 @@ func (f *Float64SliceFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *Float64SliceFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Float64Slice(f.Name))
+	}
+
+	return nil
+}
+
 // Float64Slice looks up the value of a local Float64SliceFlag, returns
 // nil if not found
 func (cCtx *Context) Float64Slice(name string) []float64 {

flag_generic.go

@@ -24,6 +24,7 @@ type GenericFlag struct {
 	Value       Generic
 	DefaultText string
 	HasBeenSet  bool
+	Action      func(*Context, interface{}) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -104,6 +105,15 @@ func (f GenericFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *GenericFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Generic(f.Name))
+	}
+
+	return nil
+}
+
 // Generic looks up the value of a local GenericFlag, returns
 // nil if not found
 func (cCtx *Context) Generic(name string) interface{} {

flag_int.go

@@ -19,6 +19,7 @@ type IntFlag struct {
 	DefaultText string
 	Destination *int
 	HasBeenSet  bool
+	Action      func(*Context, int) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -102,6 +103,15 @@ func (f *IntFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *IntFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Int(f.Name))
+	}
+
+	return nil
+}
+
 // Int looks up the value of a local IntFlag, returns
 // 0 if not found
 func (cCtx *Context) Int(name string) int {

flag_int64.go

@@ -19,6 +19,7 @@ type Int64Flag struct {
 	DefaultText string
 	Destination *int64
 	HasBeenSet  bool
+	Action      func(*Context, int64) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -101,6 +102,15 @@ func (f *Int64Flag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *Int64Flag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Int64(f.Name))
+	}
+
+	return nil
+}
+
 // Int64 looks up the value of a local Int64Flag, returns
 // 0 if not found
 func (cCtx *Context) Int64(name string) int64 {

flag_int64_slice.go

@@ -88,6 +88,7 @@ type Int64SliceFlag struct {
 	Value       *Int64Slice
 	DefaultText string
 	HasBeenSet  bool
+	Action      func(*Context, []int64) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -176,6 +177,15 @@ func (f *Int64SliceFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *Int64SliceFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Int64Slice(f.Name))
+	}
+
+	return nil
+}
+
 // Int64Slice looks up the value of a local Int64SliceFlag, returns
 // nil if not found
 func (cCtx *Context) Int64Slice(name string) []int64 {

flag_int_slice.go

@@ -99,6 +99,7 @@ type IntSliceFlag struct {
 	Value       *IntSlice
 	DefaultText string
 	HasBeenSet  bool
+	Action      func(*Context, []int) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -187,6 +188,15 @@ func (f *IntSliceFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *IntSliceFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.IntSlice(f.Name))
+	}
+
+	return nil
+}
+
 // IntSlice looks up the value of a local IntSliceFlag, returns
 // nil if not found
 func (cCtx *Context) IntSlice(name string) []int {

flag_path.go

@@ -18,6 +18,7 @@ type PathFlag struct {
 	DefaultText string
 	Destination *string
 	HasBeenSet  bool
+	Action      func(*Context, string) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -96,6 +97,15 @@ func (f *PathFlag) Apply(set *flag.FlagSet) error {
 	return nil
 }
 
+// RunAction executes flag action if set
+func (f *PathFlag) RunAction(c *Context) error {
+	if f.Action != nil {
+		return f.Action(c, c.Path(f.Name))
+	}
+
+	return nil
+}
+
 // Path looks up the value of a local PathFlag, returns
 // "" if not found
 func (cCtx *Context) Path(name string) string {