hardhat-zksync-solc

This plugin is used to provide a convenient interface for compiling Solidity smart contracts before deploying them to zkSync Era.

Learn more about the latest updates in the changelog

Prerequisite

To use the hardhat-zksync-solc in your project, we recommend that:

• You have a Node installation and yarn or npm package manager.

Installation

@matterlabs/hardhat-zksync-solc

Add the latest version of this plugin to your project with the following command:

yarn add -D @matterlabs/hardhat-zksync-solc

npm i -D @matterlabs/hardhat-zksync-solc

Configuration

Import the package in the hardhat.config.ts file:

import "@matterlabs/hardhat-zksync-solc";

Default config in hardhat-zksync-solc ^0.4.0

Version 0.4.0 introduced a default configuration making all parameters optional. You can override the default configuration in the hardhat.config.ts file.

Support for missing libraries in hardhat-zksync-solc ^0.4.2

Version 0.4.2 introduced a mode that detects non-inlinable libraries that are missing and that are required for the compilation of contracts. This feature works with the hardhat-zksync-deploy plugin, specifically the deploy-zksync:libraries task, to compile and deploy the missing libraries. There are no new commands, just follow the instructions logged by the yarn hardhat compile output.

Upon encountering missing non-inline libraries during the compilation process, the compiler logged steps to follow, while compilation is not valid. This results with empty artifacts-zk and cache-zk folders.

Any configuration parameters should be added inside a zksolc property in the hardhat.config.ts file:

zksolc: {
    version: "latest", // optional.
    settings: {
      compilerPath: "zksolc",  // optional. Ignored for compilerSource "docker". Can be used if compiler is located in a specific folder
      libraries:{}, // optional. References to non-inlinable libraries
      missingLibrariesPath: "./.zksolc-libraries-cache/missingLibraryDependencies.json", // optional. This path serves as a cache that stores all the libraries that are missing or have dependencies on other libraries. A `hardhat-zksync-deploy` plugin uses this cache later to compile and deploy the libraries, especially when the `deploy-zksync:libraries` task is executed
      isSystem: false, // optional.  Enables Yul instructions available only for zkSync system contracts and libraries
      forceEvmla: false, // optional. Falls back to EVM legacy assembly if there is a bug with Yul
      optimizer: {
        enabled: true, // optional. True by default
        mode: '3', // optional. 3 by default, z to optimize bytecode size
        fallback_to_optimizing_for_size: false, // optional. Try to recompile with optimizer mode "z" if the bytecode is too large
      },
      experimental: {
        dockerImage: '', // deprecated
        tag: ''   // deprecated
      },
      contractsToCompile: [] //optional. Compile only specific contracts
    }
},

Note

• Compilers are no longer released as Docker images and its usage is no longer recommended.

• version is the zksolc compiler version. Compiler versions can be found in the following repository.
• compilerSource indicates the compiler source and can be either binary (default) or docker (deprecated). If there isn't a compiler binary already installed, the plugin will automatically download it.
• compilerPath (optional) is a field with the path to the zksolc binary. By default, the binary in $PATH is used.
• libraries if your contract uses non-inlinable libraries as dependencies, they have to be defined here. Learn more about compiling libraries here
• missingLibrariesPath (optional) serves as a cache that stores all the libraries that are missing or have dependencies on other libraries. A hardhat-zksync-deploy plugin uses this cache later to compile and deploy the libraries, especially when the deploy-zksync:libraries task is executed. Defaults to ./.zksolc-libraries-cache/missingLibraryDependencies.json.
• isSystem - required if contracts use enables Yul instructions available only for zkSync system contracts and libraries
• forceEvmla - falls back to EVM legacy assembly if there is an issue with the Yul IR compilation pipeline.
• optimizer - Compiler optimizations:
  • enabled: true (default) or false.
  • mode: 3 (default) recommended for most projects. Mode z reduces bytecode size for large projects that make heavy use of keccak and far calls.
  • fallback_to_optimizing_for_size (optional) indicates that the compiler will try to recompile with optimizer mode "z" if the bytecode is too large.
• metadata: Metadata settings. If the option is omitted, the metadata hash appends by default:
  • bytecodeHash: Can only be none. It removes metadata hash from the bytecode.
• dockerImage and tag are deprecated options used to identify the name of the compiler docker image.
• contractsToCompile (optional) field is utilized to compile only the specified contracts. The contract names do not necessarily need to be written in full qualified form. The plugin will perform an include operation, attempting to match the provided contract names.

forceEvmla usage

Setting the forceEvmla field to true can have the following negative impacts:

• No support for recursion.
• No support for internal function pointers.
• Possible contract size and performance impact.

For Solidity versions older than 0.8, only this compilation mode is available and it is used by default.

fallback_to_optimizing_for_size usage

fallback_to_optimizing_for_size option is supported for zksolc compiler version 1.3.21 or higher.

Compiler informations

The zksolc compilers are stored in the cache folder with the path {cache}/hardhat-nodejs/compilers-v2/zksolc. In this location, you can inspect the locally stored compiler versions.

{cache} is a placeholder for a path that is resolved by Hardhat

The compilerVersion.json file is used by the plugin to get the latest available version and the minimum required compiler version. This file undergoes invalidation every 24 hours (currently), subsequently being updated with fresh information. This approach is implemented to provide a caching mechanism, avoiding the risk of encountering GitHub throttling issues during fetching new releases.

zkSync Era Solidity compiler

Due to the identified limitations of the upstream Solidity compiler, our team has developed a new edition of the compiler, which effectively addresses and resolves these constraints.

For usage of EraVM compiler, eraVersion should be added inside solidity property in the hardhat.config.ts file:

solidity: {
    version: "0.8.17",
    eraVersion: "1.0.0" //optional. Compile contracts with EraVM compiler
},

• eraVersion - (optional) field used to specify version of EraVM compiler

eraVersion usage

Using latest as the field value is not supported. Instead, the eraVersion field must be filled with a specific version.

EraVM compiler usage

To use the EraVM compiler, the zksolc compiler version must be equal to or greater than 1.3.22.

Network configuration

Configure the zksync parameter in the networks to enable the zksolc compiler:

defaultNetwork: "zkSyncTestnet",
networks: {
  sepolia: {
    url: "https://sepolia.infura.io/v3/<API_KEY>", // The Ethereum Web3 RPC URL (optional).
    zksync: false, // disables zksolc compiler
  },
  zkSyncTestnet: {
    url: "https://sepolia.era.zksync.dev", // The testnet RPC URL of zkSync Era network.
    ethNetwork: "sepolia", // The Ethereum Web3 RPC URL, or the identifier of the network (e.g. `mainnet` or `sepolia`)
    zksync: true, // enables zksolc compiler
  }
},

• zksync network option indicates whether zksolc is enabled on a certain network. false by default. Useful for multichain projects in which you can enable zksync only for specific networks.

Commands

yarn hardhat compile

npx hardhat compile

Compiles all the smart contracts in the contracts directory and creates the artifacts-zk folder with all the compilation artifacts, including factory dependencies for the contracts, which could be used for contract deployment.

To understand what the factory dependencies are, read more about them in the Web3 API documentation.

Troubleshooting

Error in plugin @matterlabs/hardhat-zksync-solc: Invalid zksolc compiler version

This error is returned when the version defined in the hardhat.config.ts file is lower than the minimal required (versions are defined in file compilerVersion.json). Update the version to solve the issue.

Why is there an unexpected end of JSON input compilation error?

This is an error that is usually thrown when compiling a large smart contract codebase.

If you encounter such an error, please do the following:

• Update the @matterlabs/hardhat-zksync-solc library and try to re-compile the smart contracts afterwards.
• If after the recompilation you get the Library not found error, then you should follow the instructions from here.