Rust scaffolding

Rust scaffolding code

Now we generate some Rust helper code to make the add method available to foreign-language bindings.

First, add uniffi to your crate as both a dependency and build-dependency. Enable the build feature for the build-dependencies. This adds the runtime support code that powers UniFFI and build-time support for generating the Rust scaffolding code.

[dependencies]
uniffi = "0.XX.0"

[build-dependencies]
uniffi = { version = "0.XX.0", features = ["build"] }

Then create a build.rs file next to Cargo.toml that uses uniffi to generate the Rust scaffolding code.

fn main() {
    uniffi::generate_scaffolding("src/math.udl").unwrap();
}

Lastly, we include the generated scaffolding code in our lib.rs using this handy macro:

#![allow(unused)]
fn main() {
uniffi::include_scaffolding!("math");
}

Note: The file name is always <namespace>.uniffi.rs.

Great! add is ready to see the outside world!

Libraries that depend on UniFFI components

Suppose you want to create a shared library that includes one or more components using UniFFI. The typical way to achieve this is to create a new crate that depends on the component crates. However, this can run into rust-lang#50007. Under certain circumstances, the scaffolding functions that the component crates export do not get re-exported by the dependent crate.

Use the uniffi_reexport_scaffolding! macro to work around this issue. If your library depends on foo_component, then add foo_component::uniffi_reexport_scaffolding!(); to your lib.rs file and UniFFI will add workaround code that forces the functions to be re-exported.

Each scaffolding function contains a hash that's derived from the UDL file. This avoids name collisions when combining multiple UniFFI components into one library.