Fix some lint warnings reported on 6.25 (#8945)

Summary:
Fix some lint warnings

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8945

Test Plan: existing tests, linters

Reviewed By: zhichao-cao

Differential Revision: D31103824

Pulled By: pdillinger

fbshipit-source-id: 4dd9b0c30fa50e588107ac6ed392b2dfb507a5d4

db/arena_wrapped_db_iter.h

@@ -34,7 +34,7 @@ class Version;
 // the same as the inner DBIter.
 class ArenaWrappedDBIter : public Iterator {
  public:
-  virtual ~ArenaWrappedDBIter() {
+  ~ArenaWrappedDBIter() override {
     if (db_iter_ != nullptr) {
       db_iter_->~DBIter();
     } else {

db/kv_checksum.h

@@ -117,7 +117,7 @@ class ProtectionInfoKVO {
   friend class ProtectionInfoKVOS<T>;
   friend class ProtectionInfoKVOC<T>;
 
-  ProtectionInfoKVO<T>(T val) : info_(val) {
+  explicit ProtectionInfoKVO<T>(T val) : info_(val) {
     static_assert(sizeof(ProtectionInfoKVO<T>) == sizeof(T), "");
   }
 
@@ -155,7 +155,7 @@ class ProtectionInfoKVOC {
  private:
   friend class ProtectionInfoKVO<T>;
 
-  ProtectionInfoKVOC<T>(T val) : kvo_(val) {
+  explicit ProtectionInfoKVOC<T>(T val) : kvo_(val) {
     static_assert(sizeof(ProtectionInfoKVOC<T>) == sizeof(T), "");
   }
 
@@ -193,7 +193,7 @@ class ProtectionInfoKVOS {
  private:
   friend class ProtectionInfoKVO<T>;
 
-  ProtectionInfoKVOS<T>(T val) : kvo_(val) {
+  explicit ProtectionInfoKVOS<T>(T val) : kvo_(val) {
     static_assert(sizeof(ProtectionInfoKVOS<T>) == sizeof(T), "");
   }
 

db/listener_test.cc

@@ -1427,12 +1427,6 @@ TEST_F(EventListenerTest, BlobDBCompactFiles) {
 
 class BlobDBFileLevelEventListener : public EventListener {
  public:
-  BlobDBFileLevelEventListener() {
-    files_started_.store(0);
-    files_created_.store(0);
-    files_deleted_.store(0);
-  }
-
   void OnBlobFileCreationStarted(
       const BlobFileCreationBriefInfo& info) override {
     files_started_++;
@@ -1471,9 +1465,9 @@ class BlobDBFileLevelEventListener : public EventListener {
   }
 
  private:
-  std::atomic<uint32_t> files_started_;
-  std::atomic<uint32_t> files_created_;
-  std::atomic<uint32_t> files_deleted_;
+  std::atomic<uint32_t> files_started_{};
+  std::atomic<uint32_t> files_created_{};
+  std::atomic<uint32_t> files_deleted_{};
 };
 
 TEST_F(EventListenerTest, BlobDBFileTest) {