Feature:(issue_269) Allow external package flag definitions (#1540)

* Feature:(issue_269) Add compatibility with external package flag definitions

* Add tests

* Add defer to remove global flag

* Use ptr to receiver for extFlag

* Add const for flag prefix to ignore

app.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
+	"strings"
 	"time"
 )
 
@@ -20,6 +21,7 @@ var (
 	errInvalidActionType    = NewExitError("ERROR invalid Action type. "+
 		fmt.Sprintf("Must be `func(*Context`)` or `func(*Context) error).  %s", contactSysadmin)+
 		fmt.Sprintf("See %s", appActionDeprecationURL), 2)
+	ignoreFlagPrefix = "test." // this is to ignore test flags when adding flags from other packages
 
 	SuggestFlag               SuggestFlagFunc    = suggestFlag
 	SuggestCommand            SuggestCommandFunc = suggestCommand
@@ -197,6 +199,14 @@ func (a *App) Setup() {
 		a.ErrWriter = os.Stderr
 	}
 
+	// add global flags added by other packages
+	flag.VisitAll(func(f *flag.Flag) {
+		// skip test flags
+		if !strings.HasPrefix(f.Name, ignoreFlagPrefix) {
+			a.Flags = append(a.Flags, &extFlag{f})
+		}
+	})
+
 	var newCommands []*Command
 
 	for _, c := range a.Commands {

app_test.go

@@ -643,6 +643,42 @@ func TestApp_RunDefaultCommandWithFlags(t *testing.T) {
 	}
 }
 
+func TestApp_FlagsFromExtPackage(t *testing.T) {
+
+	var someint int
+	flag.IntVar(&someint, "epflag", 2, "ext package flag usage")
+
+	// Based on source code we can reset the global flag parsing this way
+	defer func() {
+		flag.CommandLine = flag.NewFlagSet(os.Args[0], flag.ExitOnError)
+	}()
+
+	a := &App{
+		Flags: []Flag{
+			&StringFlag{
+				Name:     "carly",
+				Aliases:  []string{"c"},
+				Required: false,
+			},
+			&BoolFlag{
+				Name:     "jimbob",
+				Aliases:  []string{"j"},
+				Required: false,
+				Value:    true,
+			},
+		},
+	}
+
+	err := a.Run([]string{"foo", "-c", "cly", "--epflag", "10"})
+	if err != nil {
+		t.Error(err)
+	}
+
+	if someint != 10 {
+		t.Errorf("Expected 10 got %d for someint", someint)
+	}
+}
+
 func TestApp_Setup_defaultsReader(t *testing.T) {
 	app := &App{}
 	app.Setup()

flag_ext.go

@@ -0,0 +1,48 @@
+package cli
+
+import "flag"
+
+type extFlag struct {
+	f *flag.Flag
+}
+
+func (e *extFlag) Apply(fs *flag.FlagSet) error {
+	fs.Var(e.f.Value, e.f.Name, e.f.Usage)
+	return nil
+}
+
+func (e *extFlag) Names() []string {
+	return []string{e.f.Name}
+}
+
+func (e *extFlag) IsSet() bool {
+	return false
+}
+
+func (e *extFlag) String() string {
+	return FlagStringer(e)
+}
+
+func (e *extFlag) IsVisible() bool {
+	return true
+}
+
+func (e *extFlag) TakesValue() bool {
+	return false
+}
+
+func (e *extFlag) GetUsage() string {
+	return e.f.Usage
+}
+
+func (e *extFlag) GetValue() string {
+	return e.f.Value.String()
+}
+
+func (e *extFlag) GetDefaultText() string {
+	return e.f.DefValue
+}
+
+func (e *extFlag) GetEnvVars() []string {
+	return nil
+}