nguyenthdat/opencode-manager

UniFFI

Use this skill for creating multi-language bindings from Rust to Kotlin and Swift. UniFFI generates a C-compatible FFI layer from Rust, then produces idiomatic foreign language bindings.

Working rules

• Choose proc-macros for new projects. #[uniffi::export] is the modern, ergonomic approach. Use UDL files only for legacy or complex cross-crate scenarios.
• The Rust crate must produce a cdylib. Set crate-type = ["cdylib"] in Cargo.toml. This is required for the shared library that Kotlin/Swift will load.
• Call uniffi::setup_scaffolding!() in lib.rs or build.rs. Proc-macros need this macro invoked once in the crate. UDL-based setups call uniffi::include_scaffolding!() instead.
• Use uniffi-bindgen to generate foreign code. Point it at the .udl file or the compiled cdylib (--library mode). Library mode is preferred for multi-crate projects.
• Async Rust maps to Kotlin coroutines (Deferred) and Swift's async/await. Requires kotlinx-coroutines-core on Android.
• Type mappings are automatic: Vec<T> → List<T> (Kotlin) / [T] (Swift), HashMap<K,V> → Map<K,V> / Dictionary<K,V>, Option<T> → T?, String → String, Vec<u8> → ByteArray / Data.
• Check exact docs before complex types. Custom types, external types, and callback interfaces have specific requirements. Refer to the official docs.

First checks

cargo install uniffi_bindgen
uniffi-bindgen --version
cargo add uniffi --features cli

Pipeline overview

Rust source (proc-macros or UDL)
       │
       ▼
  uniffi::setup_scaffolding!()
       │
       ▼
  cargo build --release          →  lib<name>.so / .dylib
       │
       ▼
  uniffi-bindgen generate        →  <name>.kt / <name>.swift
       │
       ▼
  Kotlin / Swift consumer code

Pick the right reference

Goal	Read
Project setup, Cargo.toml, build.rs, first scaffold	references/getting-started.md
Rust API: proc macros, UDL, types, objects, errors, async	references/rust-api.md
Kotlin: bindings generation, Gradle, consumer code, coroutines	references/kotlin-bindings.md
Swift: bindings generation, iOS integration, consumer code, module	references/swift-bindings.md

Load only the relevant reference file before writing code.

Rust → Kotlin / Swift type map

Rust	Kotlin	Swift
bool	Boolean	Bool
u8–u64, i8–i64	UByte–ULong, Byte–Long	UInt8–UInt64, Int8–Int64
f32, f64	Float, Double	Float, Double
String	String	String
Vec<T>	List<T>	[T]
HashMap<K,V>	Map<K,V>	Dictionary<K,V>
Option<T>	T?	T?
Vec<u8>	ByteArray	Data
()	Unit	Void / ()
SystemTime	java.time.Instant	Date
Duration	java.time.Duration	TimeInterval