From 5d7703774f4e8a9a4cb7c3d031e66771125b8b20 Mon Sep 17 00:00:00 2001
From: Alec Thomas <alec@swapoff.org>
Date: Sun, 23 Sep 2018 19:59:25 +1000
Subject: [PATCH] Validate enums (finally).

---
 context.go   | 11 +++++++++++
 kong_test.go |  8 ++++++++
 model.go     |  5 +++++
 3 files changed, 24 insertions(+)

diff --git a/context.go b/context.go
index fca1e81..7f67199 100644
--- a/context.go
+++ b/context.go
@@ -119,6 +119,17 @@ func (c *Context) Empty() bool {
 
 // Validate the current context.
 func (c *Context) Validate() error {
+	err := Visit(c.Model, func(node Visitable, next Next) error {
+		if value, ok := node.(*Value); ok {
+			if value.Enum != "" && !value.EnumMap()[fmt.Sprintf("%v", value.Target.Interface())] {
+				return fmt.Errorf("%s must be one of %s but got %q", value.Summary(), value.Enum, value.Target.Interface())
+			}
+		}
+		return next(nil)
+	})
+	if err != nil {
+		return err
+	}
 	for _, resolver := range c.combineResolvers() {
 		if err := resolver.Validate(c.Model); err != nil {
 			return err
diff --git a/kong_test.go b/kong_test.go
index b3e8d16..5278c54 100644
--- a/kong_test.go
+++ b/kong_test.go
@@ -654,3 +654,11 @@ func TestHooksCalledForDefault(t *testing.T) {
 	require.Equal(t, "default", string(cli.Flag))
 	require.Equal(t, []string{"before:default", "after:default"}, ctx.values)
 }
+
+func TestEnum(t *testing.T) {
+	var cli struct {
+		Flag string `enum:"a,b,c"`
+	}
+	_, err := mustNew(t, &cli).Parse([]string{"--flag", "d"})
+	require.EqualError(t, err, "--flag=STRING must be one of a,b,c but got \"\"")
+}
diff --git a/model.go b/model.go
index 5b90741..6256379 100644
--- a/model.go
+++ b/model.go
@@ -269,6 +269,11 @@ func (v *Value) IsBool() bool {
 
 // Parse tokens into value, parse, and validate, but do not write to the field.
 func (v *Value) Parse(scan *Scanner, target reflect.Value) error {
+	defer func() {
+		if err := recover(); err != nil {
+			panic(fmt.Sprintf("mapper %T failed to apply to %s: %s", v.Mapper, v.Summary(), err))
+		}
+	}()
 	err := v.Mapper.Decode(&DecodeContext{Value: v, Scan: scan}, target)
 	if err != nil {
 		return fmt.Errorf("%s: %s", v.Summary(), err)