Hardhat Smart Compare

Hardhat plugin to compare contracts between upgrades to ensure storage compatibility.

What

This plugin generates a storage layout snapshot of the contracts in the project. It is precious for upgradable systems, as it helps you verify that the storage layout of the proxy contracts remains unchanged after the upgrade is done.

Installation

npm install --save-dev @solarity/hardhat-smart-compare

And add the following statement to your hardhat.config.js:

require("@solarity/hardhat-smart-compare");

Or, if you are using TypeScript, add this to your hardhat.config.ts:

import "@solarity/hardhat-smart-compare";

Tasks

There are two tasks:

• storage:save task, which allows you to save the snapshot of the storage layout.
• storage:compare task, which allows you to compare the current version of contracts with the previously saved snapshot.

To view the available options, run the command (help command):

npx hardhat help storage:save 
npx hardhat help storage:compare 

Environment extensions

This plugin does not extend the environment.

Usage

To make a snapshot of the storage layout, run the following command:

npx hardhat storage:save

To compare the current version of contracts with the previously saved snapshot, run the following command:

npx hardhat storage:compare

How it works

The plugin completes the compile task, retrieves artifacts from the Hardhat Runtime Environment (HRE), and performs the following actions depending on the task:

• save:

It will parse the build-info file to get the compiler output and retrieve storage layout of contracts from the outputSelection field. After that it will parse and save the storage layout for each contract with an inheritance "map" in a JSON file.

• compare:

Initially, it will execute the same steps as the save task. It will then thoroughly compare the existing snapshot and the newly generated version, scrutinizing each field and type. Ultimately, if the --print-diff flag is provided, it will display any differences that were identified.

Configuration

The default configuration looks as follows. You may customize all fields in your hardhat config file.

module.exports = {
  compare: {
    snapshotPath: "./storage_snapshots",
    snapshotFileName: "storage_snapshot.json",
  },
};

Parameter explanation

• snapshotPath: Path to the directory where the storage layout snapshot is saved.
• snapshotFileName: File name of the snapshot.

Known limitations

• Doesn't detect non-storage variables changes.
• Printed results are hard to comprehend.
• Vyper is currently not supported.