Features

Check why and how a dependency in your workspace gets enabled. This is useful in cases where you encounter weird build errors which are caused by unintentional inclusion of dependencies or features.

Install

bash cargo install -f feature

Example - Fixing feature propagation

Let's check that the runtime-benchmarks feature is properly passed down to all the dependencies of the frame-support crate in the workspace of [Substrate]:

bash feature lint propagate-feature --manifest-path ../substrate/Cargo.toml --feature runtime-benchmarks --workspace -p frame-support

The output reveals that there are some dependencies that expose the feature but don't get it passed down:

pre Analyzing workspace crate "frame-support" feature "runtime-benchmarks" must propagate to: frame-system sp-runtime sp-staking Generated 1 errors and 0 warnings and fixed 0 issues.

Without the --workspace it even detects 243 violations.

Now you can verify this for the frame-support which is indeed missing the feature for sp-runtime while that is clearly sp-runtime it 🤔.

This can be fixed by applying the --fix flag like:

bash feature lint propagate-feature --manifest-path ../substrate/Cargo.toml --feature runtime-benchmarks --workspace -p frame-support --fix

Which results in this diff:

patch -runtime-benchmarks = [] +runtime-benchmarks = [ + "frame-system/runtime-benchmarks", + "sp-runtime/runtime-benchmarks", + "sp-staking/runtime-benchmarks" +]

The auto-fix is currently a bit coarse, and does not check for optional dependencies. It will also not add the feature to crates that do not have it, but need it because of a dependency. This will be fixed soon.

Example - Dependency tracing

Recently there was a build error in the Substrate master CI which was caused by a downstream dependency snow. To investigate this, it is useful to see how Substrate depends on it.

Let's find out how node-cli depends on snow:

bash feature trace --manifest-path substrate/Cargo.toml node-cli snow

output:

node-cli -> try-runtime-cli -> substrate-rpc-client -> sc-rpc-api ->sc-chain-spec -> sc-telemetry -> libp2p -> libp2p-webrtc -> libp2p-noise -> snow

So it comes from libp2p, okay. Good to know.

Roadmap