How kotlinx.serialization generates code: a compiler plugin deep dive

Kotlinx.serialization serves as the standard serialization library for Kotlin, providing features such as compile-time code generation, multiplatform support, and format-agnostic design. By annotating a class with @Serializable, developers benefit from the library's ability to handle serialization without the need for reflection, which can be slow and platform-dependent. The library achieves this through a sophisticated two-pass IR generation strategy that first creates function declarations with empty bodies before filling in implementations, allowing for efficient handling of forward references. The plugin generates a nested $serializer class with methods for serialization and deserialization, and employs optimizations such as the golden mask pattern for validating required fields, enhancing performance and safety. It also supports both the K1 and K2 compiler frontends, ensuring compatibility during Kotlin's transition to a new frontend. Understanding these mechanisms aids developers in creating custom serializers, debugging, and effectively utilizing the library for various projects, including those requiring cross-platform consistency or handling complex API responses.