Validate after everything is applied.

Fixes #27.

context.go

@@ -135,7 +135,7 @@ 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 fmt.Errorf("%s must be one of %s but got %q", value.ShortSummary(), value.Enum, value.Target.Interface())
 			}
 		}
 		return next(nil)

defaults.go

@@ -14,9 +14,8 @@ func ApplyDefaults(target interface{}, options ...Option) error {
 	if err != nil {
 		return err
 	}
-	err = ctx.Validate()
-	if err != nil {
+	if err = ctx.ApplyDefaults(); err != nil {
 		return err
 	}
-	return ctx.ApplyDefaults()
+	return ctx.Validate()
 }

kong.go

@@ -209,10 +209,10 @@ func (k *Kong) Parse(args []string) (ctx *Context, err error) {
 	if err = k.applyHook(ctx, "BeforeApply"); err != nil {
 		return nil, &ParseError{error: err, Context: ctx}
 	}
-	if err = ctx.Validate(); err != nil {
+	if _, err = ctx.Apply(); err != nil {
 		return nil, &ParseError{error: err, Context: ctx}
 	}
-	if _, err = ctx.Apply(); err != nil {
+	if err = ctx.Validate(); err != nil {
 		return nil, &ParseError{error: err, Context: ctx}
 	}
 	if err = k.applyHook(ctx, "AfterApply"); err != nil {

kong_test.go

@@ -680,7 +680,7 @@ func TestEnum(t *testing.T) {
 		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 \"\"")
+	require.EqualError(t, err, "--flag must be one of a,b,c but got \"d\"")
 }
 
 type commandWithHook struct {
@@ -734,5 +734,18 @@ func TestDefaultEnumValidated(t *testing.T) {
 	}
 	p := mustNew(t, &cli)
 	_, err := p.Parse(nil)
-	require.Error(t, err)
+	require.EqualError(t, err, "--flag must be one of valid but got \"invalid\"")
+}
+
+func TestEnvarEnumValidated(t *testing.T) {
+	restore := tempEnv(map[string]string{
+		"FLAG": "invalid",
+	})
+	defer restore()
+	var cli struct {
+		Flag string `env:"FLAG" enum:"valid" default:"valid"`
+	}
+	p := mustNew(t, &cli)
+	_, err := p.Parse(nil)
+	require.EqualError(t, err, "--flag must be one of valid but got \"invalid\"")
 }