feature-manifest

feature-manifest is a small Rust crate plus Cargo subcommand for documenting, validating, and rendering Cargo feature flags.

It gives crate authors a place to describe feature intent today, using Cargo.toml, while also producing outputs that are useful for README tables, docs pages, CI, and editor tooling.

As of 2026-05-02, a quick cargo search for both feature-manifest and cargo-feature-manifest returned no matches, so the crate name appears open on crates.io.

Why this exists

Cargo features are powerful, but feature intent is often trapped in a raw [features] table. feature-manifest creates a lightweight authoring layer on top of that table so maintainers can:

• keep every feature documented in one place,
• fail CI when metadata drifts out of sync,
• generate Markdown for docs and READMEs,
• emit JSON for tooling and editor integrations,
• visualize feature relationships with Mermaid.

Installation

Once published:

cargo install feature-manifest

This installs the cargo-feature-manifest binary, which you then invoke as cargo feature-manifest.

From source today:

git clone https://github.com/funwithcthulhu/feature-manifest.git
cd feature-manifest
cargo install --path .

Commands

cargo feature-manifest check
cargo feature-manifest markdown > FEATURES.md
cargo feature-manifest json
cargo feature-manifest graph

The default command is check, so cargo feature-manifest is valid shorthand.

During local development, you can run the same commands with:

cargo run -- check
cargo run -- markdown
cargo run -- json
cargo run -- graph

You can point the tool at another crate with either a crate directory or a direct manifest path:

cargo feature-manifest check --manifest-path path/to/crate
cargo feature-manifest markdown --manifest-path path/to/crate/Cargo.toml

Metadata format

Structured form:

[features]
default = ["serde"]
serde = ["dep:serde"]
tokio = ["dep:tokio"]
unstable = []
internal-codegen = []

[package.metadata.feature-manifest.features]
serde = { description = "Enables Serialize/Deserialize impls." }
tokio = { description = "Enables async APIs backed by Tokio." }
unstable = { description = "Experimental APIs; semver not guaranteed.", unstable = true }
internal-codegen = { description = "Internal codegen support.", public = false }

[[package.metadata.feature-manifest.groups]]
name = "runtime"
description = "Choose one async runtime backend."
members = ["tokio", "async-std"]
mutually_exclusive = true

Flat shorthand is also supported:

[package.metadata.feature-manifest]
serde = "Enables Serialize/Deserialize impls."
tokio = { description = "Enables async APIs backed by Tokio." }

Supported metadata fields:

Group fields:

What check validates

• Features declared in [features] but missing metadata.
• Metadata entries that do not correspond to a real feature.
• Empty or missing descriptions.
• Unstable, deprecated, or private features that are enabled by default without allow_default = true.
• Mutually exclusive groups that default-enable more than one member.
• Unknown or duplicate feature names inside configured groups.

Output goals

• markdown produces a docs-friendly feature table.
• json emits normalized machine-readable metadata.
• graph emits a Mermaid dependency graph for feature relationships.

Example JSON output shape:

{
  "package_name": "demo",
  "features": {
    "serde": {
      "name": "serde",
      "default_enabled": true,
      "dependencies": ["dep:serde"],
      "has_metadata": true,
      "metadata": {
        "description": "Enables Serialize/Deserialize impls.",
        "public": true,
        "unstable": false,
        "deprecated": false,
        "allow_default": false,
        "note": null
      }
    }
  }
}

Example Mermaid output:

graph TD
    default_["default"]
    feature_serde["serde\nstable, default"]
    feature_tokio["tokio\nstable"]
    ref_dep_serde["dep:serde"]
    ref_dep_tokio["dep:tokio"]
    default_ --> feature_serde
    feature_serde --> ref_dep_serde
    feature_tokio --> ref_dep_tokio

Dogfooding Fixture

A small sample crate lives at fixtures/basic/Cargo.toml. You can try the current CLI against it with:

cargo run -- check --manifest-path fixtures/basic
cargo run -- markdown --manifest-path fixtures/basic
cargo run -- graph --manifest-path fixtures/basic

Publish Checklist

• Confirm the version, CHANGELOG.md, and README examples are ready for the release.
• Run cargo fmt, cargo test, and cargo publish --dry-run.
• Install the binary locally with cargo install --path . and smoke-test the CLI against a real crate.
• Generate and review FEATURES.md output from a non-trivial fixture crate.

Why this layout

The crate is split into a reusable library and a cargo-feature-manifest binary so the validation logic stays testable and future integrations can call the library directly.

License

Licensed under either of the following, at your option:

• Apache License, Version 2.0
• MIT license