Check usages of empty features

What it does

Check for all "empty" features in Cargo.toml (a_feature = []), with no optional dependency name collisions, and try to find if any config attribute in the file has that feature, if it doesn't, raise.

Lint Name

unused_crate_feature

Category

pedantic

Advantage

• Allow libraries to clean up unused features, which could then signal downstream that something has changed.
• Cleaner code and crates, with less "cruft"

Drawbacks

Possible false-positives if cargo were to infer more from features in the future (other than optional dependencies and the likes)

Example

[features]
a_thing = []

This feature is nowhere to be found in any source code, so this raises the warning.

Start with the [features] section in Cargo.toml and the source code that handles crate features and config attributes. Check how optional dependency name collisions and feature references are represented before defining the lint. Done means unused_crate_feature reports empty features with no optional dependency collision when no source configuration attribute uses them.