ZkSync/ZkSynk.go package contain generated wrapper for zkSync smart contract.
ERC20/ERC20.go package contain generated wrapper for default ERC20 smart contract.
This code was generated by abigen tool, which included in github.com/ethereum/go-ethereum devtools.
Sample of generating commands from this dir is:
abigen --abi=./ZkSync.json --pkg=ZkSync --out=./ZkSync/ZkSync.go
abigen --abi=./ERC20.json --pkg=ERC20 --out=./ERC20/ERC20.go
where files ZkSync.json and ERC20.json must be an appropriate ABI's in JSON format.