Simplify HelpPrinter and CustomHelpPrinter behaviors

help.go

@@ -47,13 +47,18 @@ type helpPrinter func(w io.Writer, templ string, data interface{})
 // Prints help for the App or Command with custom template function.
 type helpPrinterCustom func(w io.Writer, templ string, data interface{}, customFunc map[string]interface{})
 
-// HelpPrinter is a function that writes the help output. If not set a default
-// is used. The function signature is:
-// func(w io.Writer, templ string, data interface{})
+// HelpPrinter is a function that writes the help output. If not set explicitly,
+// this calls HelpPrinterCustom using only the default template functions.
+//
+// If custom logic for printing help is required, this function can be
+// overridden. If the ExtraInfo field is defined on an App, this function
+// should not be modified, as HelpPrinterCustom will be used directly in order
+// to capture the extra information.
 var HelpPrinter helpPrinter = printHelp
 
-// HelpPrinterCustom is same as HelpPrinter but
-// takes a custom function for template function map.
+// HelpPrinterCustom is a function that writes the help output. It is used as
+// the default implementation of HelpPrinter, and may be called directly if
+// the ExtraInfo field is set on an App.
 var HelpPrinterCustom helpPrinterCustom = printHelpCustom
 
 // VersionPrinter prints the version for the App
@@ -66,20 +71,24 @@ func ShowAppHelpAndExit(c *Context, exitCode int) {
 }
 
 // ShowAppHelp is an action that displays the help.
-func ShowAppHelp(c *Context) (err error) {
-	if c.App.CustomAppHelpTemplate == "" {
-		HelpPrinter(c.App.Writer, AppHelpTemplate, c.App)
-		return
+func ShowAppHelp(c *Context) error {
+	template := c.App.CustomAppHelpTemplate
+	if template == "" {
+		template = AppHelpTemplate
 	}
+
+	if c.App.ExtraInfo == nil {
+		HelpPrinter(c.App.Writer, template, c.App)
+		return nil
+	}
+
 	customAppData := func() map[string]interface{} {
-		if c.App.ExtraInfo == nil {
-			return nil
-		}
 		return map[string]interface{}{
 			"ExtraInfo": c.App.ExtraInfo,
 		}
 	}
-	HelpPrinterCustom(c.App.Writer, c.App.CustomAppHelpTemplate, c.App, customAppData())
+	HelpPrinterCustom(c.App.Writer, template, c.App, customAppData())
+
 	return nil
 }
 
@@ -186,11 +195,13 @@ func ShowCommandHelp(ctx *Context, command string) error {
 
 	for _, c := range ctx.App.Commands {
 		if c.HasName(command) {
-			if c.CustomHelpTemplate != "" {
-				HelpPrinterCustom(ctx.App.Writer, c.CustomHelpTemplate, c, nil)
-			} else {
-				HelpPrinter(ctx.App.Writer, CommandHelpTemplate, c)
+			templ := c.CustomHelpTemplate
+			if templ == "" {
+				templ = CommandHelpTemplate
 			}
+
+			HelpPrinter(ctx.App.Writer, templ, c)
+
 			return nil
 		}
 	}
@@ -238,11 +249,15 @@ func ShowCommandCompletions(ctx *Context, command string) {
 
 }
 
-func printHelpCustom(out io.Writer, templ string, data interface{}, customFunc map[string]interface{}) {
+// printHelpCustom is the default implementation of HelpPrinterCustom.
+//
+// The customFuncs map will be combined with a default template.FuncMap to
+// allow using arbitrary functions in template rendering.
+func printHelpCustom(out io.Writer, templ string, data interface{}, customFuncs map[string]interface{}) {
 	funcMap := template.FuncMap{
 		"join": strings.Join,
 	}
-	for key, value := range customFunc {
+	for key, value := range customFuncs {
 		funcMap[key] = value
 	}
 
@@ -261,7 +276,7 @@ func printHelpCustom(out io.Writer, templ string, data interface{}, customFunc m
 }
 
 func printHelp(out io.Writer, templ string, data interface{}) {
-	printHelpCustom(out, templ, data, nil)
+	HelpPrinterCustom(out, templ, data, nil)
 }
 
 func checkVersion(c *Context) bool {