From a341a59d82867c96d0d1abfa2161bfc8d584dd60 Mon Sep 17 00:00:00 2001
From: Alec Thomas <alec@swapoff.org>
Date: Wed, 20 Nov 2019 17:36:53 +1100
Subject: [PATCH] Don't validate enum values for unused required paths.

Fixes #40.
---
 context.go   | 17 +++++++++++++++--
 kong_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/context.go b/context.go
index 80c262f..9baca0e 100644
--- a/context.go
+++ b/context.go
@@ -132,10 +132,10 @@ func (c *Context) Empty() bool {
 }
 
 // Validate the current context.
-func (c *Context) Validate() error {
+func (c *Context) Validate() error { // nolint: gocyclo
 	err := Visit(c.Model, func(node Visitable, next Next) error {
 		if value, ok := node.(*Value); ok {
-			if value.Enum != "" {
+			if value.Enum != "" && (!value.Required || value.Default != "") {
 				if err := checkEnum(value, value.Target); err != nil {
 					return err
 				}
@@ -152,6 +152,19 @@ func (c *Context) Validate() error {
 		}
 	}
 	for _, path := range c.Path {
+		var value *Value
+		switch {
+		case path.Flag != nil:
+			value = path.Flag.Value
+
+		case path.Positional != nil:
+			value = path.Positional
+		}
+		if value != nil && value.Tag.Enum != "" {
+			if err := checkEnum(value, value.Target); err != nil {
+				return err
+			}
+		}
 		if err := checkMissingFlags(path.Flags); err != nil {
 			return err
 		}
diff --git a/kong_test.go b/kong_test.go
index b6fcc5f..75a7fcd 100644
--- a/kong_test.go
+++ b/kong_test.go
@@ -791,3 +791,27 @@ func TestEnumSequence(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, []string{"a"}, cli.State)
 }
+
+func TestIssue40EnumAcrossCommands(t *testing.T) {
+	var cli struct {
+		One struct {
+			OneArg string `arg:"" required:""`
+		} `cmd:""`
+		Two struct {
+			TwoArg string `arg:"" enum:"a,b,c" required:""`
+		} `cmd:""`
+		Three struct {
+			ThreeArg string `arg:"" optional:"" default:"a" enum:"a,b,c"`
+		} `cmd:""`
+	}
+
+	p := mustNew(t, &cli)
+	_, err := p.Parse([]string{"one", "two"})
+	require.NoError(t, err)
+	_, err = p.Parse([]string{"two", "d"})
+	require.Error(t, err)
+	_, err = p.Parse([]string{"three", "d"})
+	require.Error(t, err)
+	_, err = p.Parse([]string{"three", "c"})
+	require.NoError(t, err)
+}