Worked on the haskell/cabal repository to enhance the reliability and debuggability of the Cabal build system, focusing on resolving incomplete selector warnings. Applied expertise in build system development and compiler internals to refactor code, introducing total getters and invariant checks at usage sites. Improved error messaging to accelerate diagnosis of build issues and reduce warning noise, thereby strengthening data handling and maintainability. Utilized Haskell to implement these targeted fixes, ensuring clearer feedback for developers and downstream users. The work delivered measurable improvements in error reporting and debugging workflows, addressing a key bug and contributing to the overall robustness of the build process.