From c6ba770ffda937f7343861146acf776577a30bcc Mon Sep 17 00:00:00 2001
From: Nick Miyake <nmiyake@palantir.com>
Date: Fri, 10 Nov 2017 09:37:15 -0800
Subject: [PATCH] Improve error message for missing required flags

Make the error message distinguish between singular and plural
to make it more human-readable.
---
 command.go      |  6 +++++-
 command_test.go | 20 ++++++++++++++++++--
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/command.go b/command.go
index 6cb64264..c50ab4e3 100644
--- a/command.go
+++ b/command.go
@@ -823,7 +823,11 @@ func (c *Command) validateRequiredFlags() error {
 	})
 
 	if len(missingFlagNames) > 0 {
-		return fmt.Errorf(`Required flag(s) "%s" have/has not been set`, strings.Join(missingFlagNames, `", "`))
+		errFmtStr := `Required flags "%s" have not been set`
+		if len(missingFlagNames) == 1 {
+			errFmtStr = `Required flag "%s" has not been set`
+		}
+		return fmt.Errorf(errFmtStr, strings.Join(missingFlagNames, `", "`))
 	}
 	return nil
 }
diff --git a/command_test.go b/command_test.go
index edffc150..cea3e99d 100644
--- a/command_test.go
+++ b/command_test.go
@@ -673,6 +673,22 @@ func TestPersistentFlagsOnChild(t *testing.T) {
 	}
 }
 
+func TestRequiredFlagsSingular(t *testing.T) {
+	c := &Command{Use: "c", Run: func(*Command, []string) {}}
+	output := new(bytes.Buffer)
+	c.SetOutput(output)
+	c.Flags().String("foo1", "", "required foo1")
+	c.MarkFlagRequired("foo1")
+
+	expected := fmt.Sprintf("Required flag %q has not been set", "foo1")
+
+	if err := c.Execute(); err != nil {
+		if err.Error() != expected {
+			t.Errorf("expected %v, got %v", expected, err.Error())
+		}
+	}
+}
+
 func TestRequiredFlags(t *testing.T) {
 	c := &Command{Use: "c", Run: emptyRun}
 	c.Flags().String("foo1", "", "")
@@ -681,7 +697,7 @@ func TestRequiredFlags(t *testing.T) {
 	c.MarkFlagRequired("foo2")
 	c.Flags().String("bar", "", "")
 
-	expected := fmt.Sprintf("Required flag(s) %q, %q have/has not been set", "foo1", "foo2")
+	expected := fmt.Sprintf("Required flags %q, %q have not been set", "foo1", "foo2")
 
 	_, err := executeCommand(c)
 	got := err.Error()
@@ -708,7 +724,7 @@ func TestPersistentRequiredFlags(t *testing.T) {
 
 	parent.AddCommand(child)
 
-	expected := fmt.Sprintf("Required flag(s) %q, %q, %q, %q have/has not been set", "bar1", "bar2", "foo1", "foo2")
+	expected := fmt.Sprintf("Required flags %q, %q, %q, %q have not been set", "bar1", "bar2", "foo1", "foo2")
 
 	_, err := executeCommand(parent, "child")
 	if err.Error() != expected {