FIx: Allow ext flags to be opt-out by default rather than opt-in

app.go

@@ -113,6 +113,9 @@ type App struct {
 	UseShortOptionHandling bool
 	// Enable suggestions for commands and flags
 	Suggest bool
+	// Allows global flags set by libraries which use flag.XXXVar(...) directly
+	// to be parsed through this library
+	AllowExtFlags bool
 
 	didSetup bool
 
@@ -199,13 +202,15 @@ 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})
-		}
-	})
+	if a.AllowExtFlags {
+		// 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
 

app_test.go

@@ -654,6 +654,7 @@ func TestApp_FlagsFromExtPackage(t *testing.T) {
 	}()
 
 	a := &App{
+		AllowExtFlags: true,
 		Flags: []Flag{
 			&StringFlag{
 				Name:     "carly",
@@ -677,6 +678,28 @@ func TestApp_FlagsFromExtPackage(t *testing.T) {
 	if someint != 10 {
 		t.Errorf("Expected 10 got %d for someint", someint)
 	}
+
+	a = &App{
+		Flags: []Flag{
+			&StringFlag{
+				Name:     "carly",
+				Aliases:  []string{"c"},
+				Required: false,
+			},
+			&BoolFlag{
+				Name:     "jimbob",
+				Aliases:  []string{"j"},
+				Required: false,
+				Value:    true,
+			},
+		},
+	}
+
+	// this should return an error since epflag shouldnt be registered
+	err = a.Run([]string{"foo", "-c", "cly", "--epflag", "10"})
+	if err == nil {
+		t.Error("Expected error")
+	}
 }
 
 func TestApp_Setup_defaultsReader(t *testing.T) {

godoc-current.txt

@@ -324,6 +324,9 @@ type App struct {
 	UseShortOptionHandling bool
 	// Enable suggestions for commands and flags
 	Suggest bool
+	// Allows global flags set by libraries which use flag.XXXVar(...) directly
+	// to be parsed through this library
+	AllowExtFlags bool
 
 	// Has unexported fields.
 }

testdata/godoc-v2.x.txt

@@ -324,6 +324,9 @@ type App struct {
 	UseShortOptionHandling bool
 	// Enable suggestions for commands and flags
 	Suggest bool
+	// Allows global flags set by libraries which use flag.XXXVar(...) directly
+	// to be parsed through this library
+	AllowExtFlags bool
 
 	// Has unexported fields.
 }