@argv_minus_one@mastodon.sdf.org One approach would be a cross crate used/unused pub item tracking with what cfgs the item has. Cargo could then report if all pub items for a feature are unused. This would only have false positives for features that are both behavior changes and API additions. This would also be useful for workspace-private crates for detecting unused code. I'm assuming this would be expensive to track, including the serializing and deserializing of intermediate state between rustc and cargo.