Add Email validation checker and tests to v2. (#134)

# Describe Request

Add Email validation checker and tests to v2.

# Change Type

New code.

v2/email.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2
+
+import (
+	"net/mail"
+	"reflect"
+)
+
+const (
+	// nameEmail is the name of the email check.
+	nameEmail = "email"
+)
+
+var (
+	// ErrNotEmail indicates that the given value is not a valid email address.
+	ErrNotEmail = NewCheckError("Email")
+)
+
+// IsEmail checks if the value is a valid email address.
+func IsEmail(value string) (string, error) {
+	_, err := mail.ParseAddress(value)
+	if err != nil {
+		return value, ErrNotEmail
+	}
+	return value, nil
+}
+
+// checkEmail checks if the value is a valid email address.
+func checkEmail(value reflect.Value) (reflect.Value, error) {
+	_, err := IsEmail(value.Interface().(string))
+	return value, err
+}
+
+// makeEmail makes a checker function for the email checker.
+func makeEmail(_ string) CheckFunc[reflect.Value] {
+	return checkEmail
+}

v2/email_test.go

@@ -0,0 +1,76 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2_test
+
+import (
+	"fmt"
+	"testing"
+
+	v2 "github.com/cinar/checker/v2"
+)
+
+func ExampleIsEmail() {
+	_, err := v2.IsEmail("test@example.com")
+	if err != nil {
+		fmt.Println(err)
+	}
+}
+
+func TestIsEmailInvalid(t *testing.T) {
+	_, err := v2.IsEmail("invalid-email")
+	if err == nil {
+		t.Fatal("expected error")
+	}
+}
+
+func TestIsEmailValid(t *testing.T) {
+	_, err := v2.IsEmail("test@example.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestCheckEmailNonString(t *testing.T) {
+	defer FailIfNoPanic(t, "expected panic")
+
+	type User struct {
+		Email int `checkers:"email"`
+	}
+
+	user := &User{}
+
+	v2.CheckStruct(user)
+}
+
+func TestCheckEmailInvalid(t *testing.T) {
+	type User struct {
+		Email string `checkers:"email"`
+	}
+
+	user := &User{
+		Email: "invalid-email",
+	}
+
+	_, ok := v2.CheckStruct(user)
+	if ok {
+		t.Fatal("expected error")
+	}
+}
+
+func TestCheckEmailValid(t *testing.T) {
+	type User struct {
+		Email string `checkers:"email"`
+	}
+
+	user := &User{
+		Email: "test@example.com",
+	}
+
+	_, ok := v2.CheckStruct(user)
+	if !ok {
+		t.Fatal("expected valid")
+	}
+}

v2/maker.go

@@ -20,6 +20,7 @@ var makers = map[string]MakeCheckFunc{
 	nameASCII:        makeASCII,
 	nameCIDR:         makeCIDR,
 	nameDigits:       makeDigits,
+	nameEmail:        makeEmail,
 	nameMaxLen:       makeMaxLen,
 	nameMinLen:       makeMinLen,
 	nameRequired:     makeRequired,