Some changes per feedback in #1368

app.go

@@ -184,14 +184,7 @@ func (a *App) Setup() {
 			c.HelpName = fmt.Sprintf("%s %s", a.HelpName, c.Name)
 		}
 
-		fc := newFlagCategories()
-		for _, fl := range c.Flags {
-			if cf, ok := fl.(CategorizableFlag); ok {
-				fc.AddFlag(cf.GetCategory(), cf)
-			}
-		}
-
-		c.flagCategories = fc
+		c.flagCategories = newFlagCategoriesFromFlags(c.Flags)
 		newCommands = append(newCommands, c)
 	}
 	a.Commands = newCommands
@@ -502,7 +495,7 @@ func (a *App) VisibleCommands() []*Command {
 // VisibleFlagCategories returns a slice containing all the categories with the flags they contain
 func (a *App) VisibleFlagCategories() []VisibleFlagCategory {
 	if a.flagCategories == nil {
-		a.flagCategories = newFlagCategories()
+		return []VisibleFlagCategory{}
 	}
 	return a.flagCategories.VisibleCategories()
 }

category.go

@@ -98,6 +98,17 @@ func newFlagCategories() FlagCategories {
 	}
 }
 
+func newFlagCategoriesFromFlags(fs []Flag) FlagCategories {
+	fc := newFlagCategories()
+	for _, fl := range fs {
+		if cf, ok := fl.(CategorizableFlag); ok {
+			fc.AddFlag(cf.GetCategory(), cf)
+		}
+	}
+
+	return fc
+}
+
 func (f *defaultFlagCategories) AddFlag(category string, fl Flag) {
 	if _, ok := f.m[category]; !ok {
 		f.m[category] = &defaultVisibleFlagCategory{name: category, m: map[string]Flag{}}

command.go

@@ -284,7 +284,7 @@ func (c *Command) startApp(ctx *Context) error {
 // VisibleFlagCategories returns a slice containing all the visible flag categories with the flags they contain
 func (c *Command) VisibleFlagCategories() []VisibleFlagCategory {
 	if c.flagCategories == nil {
-		c.flagCategories = newFlagCategories()
+		return []VisibleFlagCategory{}
 	}
 	return c.flagCategories.VisibleCategories()
 }