Building the contract

Now that our contract correctly compiles into Wasm, let's digest our build command.

$ cargo build --target wasm32-unknown-unknown --release --lib

The --target argument tells cargo to perform cross-compilation for a given target, instead of building a native binary for an OS it is running on. In this case the target is wasm32-unknown-unknown, which is a fancy name for Wasm target.

Our contract would be also properly compiled without --lib flag, but later, when we add query, this flag will be required, so using it from the beginning is a good habit.

Additionally, I passed the --release argument to the command - it is not required, but in most cases, debug information is not very useful while running on-chain. It is crucial to reduce the uploaded binary size for gas cost minimization. It is worth knowing that there is a CosmWasm Rust Optimizer tool that takes care of building even smaller binaries. For production, all the contracts should be compiled using this tool, but it is now not essential for learning purposes.

Aliasing build command

Now I see you are disappointed in building your contracts with some overcomplicated command instead of simple cargo build. Hopefully, it is not the case. The common practice is to alias the building command, to make it as simple as building a native application.

Let's create .cargo/config file in your contract project directory with the following content:

[alias]
wasm = "build --target wasm32-unknown-unknown --release --lib"
wasm-debug = "build --target wasm32-unknown-unknown --lib"

Building your Wasm binary is now as easy as executing cargo wasm. We also added the additional wasm-debug command for rare cases, when we want to build the Wasm binary with debug information included.

Checking contract validity

When the contract is built, the last step to ensure that it is a valid CosmWasm contract is to call cosmwasm-check on it:

$ cargo wasm
    .
    . (compilation messages)
    .
    Finished release [optimized] target(s) in 0.03s

$ cosmwasm-check target/wasm32-unknown-unknown/release/contract.wasm
Available capabilities: {"cosmwasm_1_1", "iterator", "staking", "stargate"}

target/wasm32-unknown-unknown/release/contract.wasm: pass

All contracts (1) passed checks!