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

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:

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:

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:

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

Which results in this diff:

-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:

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

• Add feature information to the enabled deps
• Allow manual skipping of dev dependencies (currently always skipped)
• Introduce filters for versions and features for argument to
• Optimize shortest_path function
• Create lint rules which can be used to validate that certain constraints in the work-space hold