To compile release version of the smart contract you can run:

cargo build --target wasm32-unknown-unknown --release

Note: The above build command is setting a target flag to create a WebAssembly .wasm file.

Notice that your project directory now has a few additional items:

.

├── Cargo.lock ⟵ created during build to lock dependencies

├── Cargo.toml

├── src

│ └── lib.rs

└── target ⟵ created during build, holds the compiled wasm

Build and Flags

We recommend you to optimize your build artifact with the use of the next flags in your Cargo.toml file. If you are performing a multi-contract build, you should include these settings in the Cargo.toml that is at the root of your project.

[profile.release]

codegen-units = 1

# Tell `rustc` to optimize for small code size.

opt-level = "z"

lto = true

debug = false

panic = "abort"

# Opt into extra safety checks on arithmetic operations https://stackoverflow.com/a/64136471/249801

overflow-checks = true

The above command is essentially setting special flags and optimizing the resulting .wasm file. At the end of the day, this allows you to customize the cargo build --release command.

Custom Flags

If you wish to add custom flags to your build, you can perform this by adding build flags to your ProjectFolder/.cargo/config.toml as illustrated in this example.

[target.wasm32-unknown-unknown]

rustflags = ["-C", "link-arg=-s"]

A full set of build options can be accessed at https://doc.rust-lang.org/cargo/reference/config.html.

You can find an example here.