Examples of compiling Rust code to ewasm contracts
These were compiled with rustc 1.25.0-nightly, and a patched wasm-gc.
$ rustup run nightly rustc --version
rustc 1.25.0-nightly (79a521bb9 2018-01-15)
$ rustup target add wasm32-unknown-unknown --toolchain nightly
$ cargo install --git https://github.com/ewasm/wasm-gc --branch keep-main-func
You also need wabt for wasm2wat.