From 64d23c54e3e2a385ce12757939bed9c632d1693c Mon Sep 17 00:00:00 2001
From: Arun Gajaraj <60968728+arun-gajaraj@users.noreply.github.com>
Date: Sun, 1 Oct 2023 04:29:49 +0530
Subject: [PATCH] Improved error message for missing required flags: now list
 all missing required flags for better user guidance. (#340)

Issue: https://github.com/alecthomas/kingpin/issues/215
---
 app.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/app.go b/app.go
index 43d816b..4f1f31b 100644
--- a/app.go
+++ b/app.go
@@ -464,14 +464,18 @@ func (a *Application) validateRequired(context *ParseContext) error {
 	}
 
 	// Check required flags and set defaults.
+	var missingFlags []string
 	for _, flag := range context.flags.long {
 		if flagElements[flag.name] == nil {
 			// Check required flags were provided.
 			if flag.needsValue() {
-				return fmt.Errorf("required flag --%s not provided", flag.name)
+				missingFlags = append(missingFlags, fmt.Sprintf("'--%s'", flag.name))
 			}
 		}
 	}
+	if len(missingFlags) != 0 {
+		return fmt.Errorf("required flag(s) %s not provided", strings.Join(missingFlags, ", "))
+	}
 
 	for _, arg := range context.arguments.args {
 		if argElements[arg.name] == nil {