public-api

List and diff the public API of Rust library crates by analyzing rustdoc JSON output files from rustdoc +nightly.

Usage

… as a Rust library

See docs.rs for library documentation and example code.

… as a CLI

Use cargo public-api for CLI use cases.

… as a CI Check

With a regular cargo test that you run in CI you will be able to

• prevent accidental changes to your public API
• review the public API diff of deliberate changes

First add the latest versions of the recommended libraries to your [dev-dependencies]:

cargo add --dev \
    rustup-toolchain \
    rustdoc-json \
    public-api

Then add the following test to your project. As the author of the below test code, I hereby associate it with CC0 and to the extent possible under law waive all copyright and related or neighboring rights to it:

#[test]
fn public_api() {
    // Install a compatible nightly toolchain if it is missing.
    rustup_toolchain::install(public_api::MINIMUM_NIGHTLY_RUST_VERSION).unwrap();

    // Build rustdoc JSON.
    let rustdoc_json = rustdoc_json::Builder::default()
        .toolchain(public_api::MINIMUM_NIGHTLY_RUST_VERSION)
        .build()
        .unwrap();

    // Derive the public API from rustdoc JSON.
    let public_api = public_api::Builder::from_rustdoc_json(rustdoc_json)
        .build()
        .unwrap();

    // Assert that the public API matches the latest snapshot.
    // Run with env var `UPDATE_SNAPSHOTS=yes` to update the snapshot.
    public_api.assert_eq_or_update("./tests/snapshots/public-api.txt");
}

Before you run the test the first time you need create a snapshot of the current public API:

UPDATE_SNAPSHOTS=yes cargo test

This creates a tests/public-api.txt file in your project that you git add together with your other project files. Then a regular

cargo test

will fail if your public API is accidentally or deliberately changed. Run

UPDATE_SNAPSHOTS=yes cargo test

again to update the public API snapshot and review the git diff.

Maintainers

See here.