Worked on the scala/scala3 repository to enhance the correctness and stability of pattern matching in Scala 3, focusing on type decomposition during subspace computations. Addressed a bug by implementing a guard that prevents incorrect right-hand side type decomposition, specifically disallowing decomposition on type parameters and deferred type references to avoid false positives. Developed comprehensive tests to verify the new guard’s effectiveness and ensure correct behavior in pattern matching scenarios. Utilized skills in compiler development, pattern matching, and type systems, working primarily with Scala. The changes improved the reliability of type decomposition logic, reducing the risk of incorrect subspace calculations.