cargo-feature-guard

Validate Cargo feature propagation across a workspace. Catches common mistakes like forgetting to forward a feature flag through intermediate crates.

What it checks

1. Feature propagation — detects crates that define a feature F but don't receive it when building an entry point with --features F
2. Never-enables — verifies that a forbidden feature is never activated in a given build context (e.g. mock must never reach c_api)
3. Duplicate dependencies — reports dependencies present in multiple versions (informational, does not fail the build)

Uses cargo tree as the source of truth, which accounts for feature unification by the Cargo resolver.

Installation

# From crates.io
cargo install cargo-feature-guard

# Or with cargo-binstall (downloads pre-built binary)
cargo binstall cargo-feature-guard

Usage

# Run in your workspace root (looks for feature-guard.toml)
cargo feature-guard

# Specify a custom config file
cargo feature-guard --config path/to/config.toml

Configuration

Create a feature-guard.toml in your workspace root:

# Define entry points and which features they should be built with.
# The tool checks that every crate defining one of these features actually
# receives it through the dependency graph.
[[entry-points]]
package = "my-app"
features = ["mock", "nfc"]

[[entry-points]]
package = "my-lib"
features = ["nfc"]

# Verify that a feature is NEVER enabled for a given package.
# Useful to ensure test-only features don't leak into production builds.
[[never-enables]]
package = "my-lib"
forbidden = "mock"

# Multiple forbidden features can be specified as an array.
[[never-enables]]
package = "my-other-lib"
forbidden = ["mock", "test-only"]

[[entry-points]]

[[never-enables]]

Exit codes

License

MIT