The author shares their experience migrating a service from Scala 2.13 to Scala 3, which initially seemed successful but later revealed performance issues. They discovered that a bug in a library caused a significant slowdown, highlighting the importance of testing and benchmarking when upgrading language versions.

tsdown is an elegant and fast bundler for libraries, leveraging Oxc and Rolldown for quick builds and declaration file generation. It supports a robust ecosystem including Rollup and Vite plugins, while offering an easy-to-use setup that allows developers to focus on coding. The tool also ensures a seamless migration from tsup, enhancing the user experience.