  Clippy lints are considered as essential tools for Rust developers, as they
can be configured as gate-keeping rules for a Rust project during continuous
integration. Despite their availability, little was known about practical
application and cost-effectiveness of the lints in reducing code quality
issues. In this study, we embark on a comprehensive analysis to unveil the true
impact of Clippy lints in the Rust development landscape. The study is
structured around three interrelated components, each contributing to the
overall effectiveness of Clippy. Firstly, we conduct a comprehensive analysis
of Clippy lints in all idiomatic crates-io Rust projects with an average
warning density of 21/KLOC. The analysis identifies the most cost-effective
lint fixes, offering valuable opportunities for optimizing code quality.
Secondly, we actively engage Rust developers through a user survey to garner
invaluable feedback on their experiences with Clippy. User insights shed light
on two crucial concerns: the prevalence of false positives in warnings and the
need for auto-fix support for most warnings. Thirdly, building upon these
findings, we engineer three innovative automated refactoring techniques to
effectively fix the four most frequent Clippy lints. As a result, the warning
density in Rosetta benchmarks has significantly decreased from 195/KLOC to an
impressive 18/KLOC, already lower than the average density of the crates-io
Rust projects. These results demonstrate tangible benefit and impact of our
efforts in enhancing the overall code quality and maintainability for Rust
developers.
