PHP 遗留代码现代化实战：坏味道识别、绞杀者模式与灰度切换

cloc src/                                                     # 规模分布
find src -name '*.php' | xargs wc -l | sort -rn | head -20     # 最大的文件
ls tests/ 2>/dev/null || echo "无测试目录"
vendor/bin/phpstan analyse src --level=0 --no-progress         # 最低等级摸底
composer outdated --direct && composer audit

composer require --dev phpmd/phpmd rector/rector
vendor/bin/phpmd src text codesize,unusedcode        # 圈复杂度与重复度
vendor/bin/rector process src --dry-run              # 列出可自动化的改动

public function test_legacy_discount_calculation_snapshot(): void
{
    $calculator = new LegacyDiscountCalculator($this->db());

    // 用真实历史数据喂进去，首次运行生成快照，之后作为回归基线
    $result = $calculator->calculate(orderId: 1001);

    $this->assertSame(1850, $result['discountCents']);
    $this->assertSame(['满减', '会员'], $result['appliedRules']);
}

public function test_legacy_order_endpoint_snapshot(): void
{
    $response = $this->post('/legacy/order/create', [
        'sku' => 'A-100', 'qty' => 2, 'user_id' => 9527,
    ]);

    $response->assertStatus(200);
    $this->assertMatchesSnapshot($response->json());   // 全量响应快照
}

阶段 1：[ 旧系统 ] ← 100%
阶段 2：[ 路由 ] ─ 80% → [ 旧系统 ]，20% → [ 新系统 ]
阶段 3：[ 路由 ] → [ 新系统 ]      [ 旧系统 ]（只读兜底）
阶段 4：关停旧系统

$feature = Feature::for($userId);
if ($feature->active('new-order-flow')) {
    return $this->forwardToNewApp($request);   // 新系统
}
return $this->legacyDispatch($request);        // 旧逻辑

// ❌ 硬编码：无法替换、无法测试
class OrderService
{
    public function notify(int $orderId): void
    {
        $client = new AliyunSmsClient('key', 'secret');   // 接缝为零
        $client->send('13800000000', "订单 {$orderId} 已发货");
    }
}

// ✅ 引入接缝：依赖从外部注入
interface SmsSender { public function send(string $to, string $msg): void; }

class OrderService
{
    public function __construct(private SmsSender $sms) {}

    public function notify(int $orderId, string $phone): void
    {
        $this->sms->send($phone, "订单 {$orderId} 已发货");
    }
}

// rector.php
return RectorConfig::configure()
    ->withPaths([__DIR__ . '/src'])
    ->withSets([
        \Rector\Set\ValueObject\LevelSetList::UP_TO_PHP_80,
        \Rector\Set\ValueObject\SetList::DEAD_CODE,
    ]);

vendor/bin/rector process src --dry-run   # 先看会改什么
vendor/bin/rector process src             # 执行（务必先提交或分支）

final class DualWriteOrderRepository implements OrderRepository
{
    public function __construct(
        private OrderRepository $legacy,
        private OrderRepository $modern,
        private LoggerInterface $logger,
    ) {}

    public function save(Order $order): void
    {
        $this->legacy->save($order);            // 主写：失败则整体失败
        try {
            $this->modern->save($order);        // 副写：失败只记录
        } catch (\Throwable $e) {
            $this->logger->error('新表写入失败', ['order' => $order->id()]);
        }
    }
}

$legacy = $this->legacy->find($id);
$modern = $this->modern->find($id);
if (!$this->equals($legacy, $modern)) {
    $this->metrics->increment('dual_read_mismatch');
}
return $legacy;   // 直到差异率归零才切换读路径

final class FeatureFlags
{
    public function __construct(private CacheInterface $cache) {}

    public function enabled(string $flag, string $userId): bool
    {
        $percent = (int) $this->cache->get("flag:{$flag}:percent", 0);
        if ($percent >= 100) { return true; }
        return $percent > 0 && (crc32($userId) % 100) < $percent;
    }
}