Update to write to a sibling file rather than a tmp one

src/watchman/WatchmanBackend.cc

@@ -238,20 +238,21 @@ std::string WatchmanBackend::clock(Watcher &watcher) {
   return found->second.stringValue();
 }
 
-void WatchmanBackend::writeSnapshot(Watcher &watcher, std::string *snapshotPath) {
+void WatchmanBackend::writeSnapshot(Watcher &watcher, std::string *inputSnapshotPath) {
   std::unique_lock<std::mutex> lock(mMutex);
   watchmanWatch(watcher.mDir);
 
-  auto clockValue = clock(watcher);
-  auto temporaryDirectory = std::filesystem::temp_directory_path();
-  auto temporaryFilePath = temporaryDirectory.append("tmp-parcel-snapshot.txt");
+  const auto clockValue = clock(watcher);
+  const auto snapshotPath = std::filesystem::path(*inputSnapshotPath);
+  auto temporaryFilePath = std::filesystem::path(snapshotPath);
+  temporaryFilePath.replace_filename(".parcel-temporary-snapshot.txt");
   {
     std::ofstream ofs(temporaryFilePath);
     ofs << clockValue;
     ofs.flush();
     ofs.close();
   }
-  std::filesystem::rename(temporaryFilePath, *snapshotPath);
+  std::filesystem::rename(temporaryFilePath, snapshotPath);
 }
 
 void WatchmanBackend::getEventsSince(Watcher &watcher, std::string *snapshotPath) {