From 52f91680210c02083c45ffb51fecdfde0ffb94f0 Mon Sep 17 00:00:00 2001
From: Onur Cinar <onur.cinar@gmail.com>
Date: Mon, 7 Sep 2026 04:20:29 +0000
Subject: [PATCH] Restore length check for required on empty array/map/slice

reflectRequired was purely IsZero()-based, but reflect.Value.IsZero()
on a slice only reports true for a nil slice -- a non-nil, zero-length
slice/map (e.g. an explicit []string{} or emails: [] in YAML) passed
required/@required silently. v1 had a dedicated length check for
Array/Map/Slice kinds; restore that behavior so an empty collection is
rejected the same way a nil one is.

Fixes #285

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CgPf2eG8h9xHh7kHFJ4eCs
---
 required.go      | 16 ++++++++++++----
 required_test.go | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/required.go b/required.go
index 977131f..1a2def6 100644
--- a/required.go
+++ b/required.go
@@ -24,13 +24,21 @@ func Required[T any](value T) (T, error) {
 	return value, err
 }
 
-// reflectRequired checks if the given value is its zero value. It
-// returns an error if the value is zero.
+// reflectRequired checks if the given value is its zero value, or an
+// empty array, map, or slice. It returns an error if so.
 func reflectRequired(value reflect.Value) (reflect.Value, error) {
 	var err error
 
-	if value.IsZero() {
-		err = ErrRequired
+	switch value.Kind() {
+	case reflect.Array, reflect.Map, reflect.Slice:
+		if value.Len() == 0 {
+			err = ErrRequired
+		}
+
+	default:
+		if value.IsZero() {
+			err = ErrRequired
+		}
 	}
 
 	return value, err
diff --git a/required_test.go b/required_test.go
index 9966878..4c7a0b8 100644
--- a/required_test.go
+++ b/required_test.go
@@ -39,3 +39,43 @@ func TestRequiredMissing(t *testing.T) {
 		t.Fatalf("got unexpected error %v", err)
 	}
 }
+
+func TestRequiredEmptySlice(t *testing.T) {
+	value := []string{}
+
+	_, err := v2.Required(value)
+
+	if !errors.Is(err, v2.ErrRequired) {
+		t.Fatalf("got unexpected error %v", err)
+	}
+}
+
+func TestRequiredNonEmptySlice(t *testing.T) {
+	value := []string{"test"}
+
+	_, err := v2.Required(value)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestRequiredEmptyMap(t *testing.T) {
+	value := map[string]string{}
+
+	_, err := v2.Required(value)
+
+	if !errors.Is(err, v2.ErrRequired) {
+		t.Fatalf("got unexpected error %v", err)
+	}
+}
+
+func TestRequiredNonEmptyMap(t *testing.T) {
+	value := map[string]string{"key": "value"}
+
+	_, err := v2.Required(value)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+}