cargo-check-external-types is a static analysis tool for Rust library authors to set and verify which types from other libraries are allowed to be are exposed in their public API. This is useful for ensuring that a breaking change to a dependency doesn't force a breaking change in the library that's using it.

The tool has two output formats to cover different use-cases:

• errors (the default): Output error messages for each type that is exposed in the public API and exit with status 1 if there is at least one error. This is useful for continuous integration.
• markdown-table: Output the places types are exposed as a Markdown table. This is intended as a discovery tool for established projects.

The tool has an optional configuration file where types can by explicitly allowed.

The test suite has a Rust library that relies on some external types. When the tool is run against this library without any configuration, it emits errors for each occurrence of an external type in the public API.

When a config file is provided, the allowed external types no longer show up in the output.

When the output format is set to markdown-table, then a table of external types is output.

Important: This tool requires a nightly build of Rust to be installed since it relies on the rustdoc JSON output, which hasn't been stabilized yet. It was last tested against nightly-2023-05-31.

To install, run the following from this README path:

cargo install --locked cargo-check-external-types

Then, in your library crate path, run:

cargo +nightly check-external-types

This will produce errors if any external types are used in a public API at all. That's not terribly useful on its own, so the tool can be given a config file to allow certain types. For example, we can allow any type in bytes with:

allowed_external_types = [
    "bytes::*",
]

Save that file somewhere in your project (in this example, we choose the name external-types.toml), and then run the command with:

cargo +nightly check-external-types --config external-types.toml

When public types and modules declared inside a #[doc(hidden)] module are reexported from a public module, they aren't checked for external types. This is because of how they are recorded in RustDoc's index. When such types and modules are encountered by this tool, a warning will be logged.

See CONTRIBUTING for more information.

This project is licensed under the Apache-2.0 License.