I found this because we only had two test cases in total for this lint. It turns out the functionality is fully covered by rustc these days. [Playground Examples](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=eb8ee6db389c77180c9fb152d3c608f4) changelog: Deprecate `unused_collect` lint. This is fully covered by rustc's `#[must_use]` on `collect` cc #2846