How to verify a contract deployed using Remix importing OpenZeppelin via GitHub?

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Hi @x5engine,

Welcome to the community :wave:
Thanks for posting in the forum :pray:

The following is an example of verifying a contract deployed using Remix importing OpenZeppelin via GitHub.

:warning: Any solution should be appropriately tested and audited.

When OpenZeppelin CLI supports verifying regular (non-upgradeable) contracts, it will be easier to deploy, interact, test and verify from the CLI. (OpenZeppelin CLI 2.8 Release Candidate supports deploy, interact and using OpenZeppelin Test Environment - testing, but doesn’t yet verify regular contracts).

I deployed the following example contract using Remix:

Token.sol

pragma solidity ^0.5.0;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.5.0/contracts/token/ERC20/ERC20.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.5.0/contracts/token/ERC20/ERC20Detailed.sol";

contract Token is ERC20, ERC20Detailed {

    constructor () public ERC20Detailed("Token", "TKN", 18) {
        _mint(msg.sender, 1000000 * (10 ** uint256(decimals())));
    }
}

I tried using the Flattener plugin for Remix but this failed to verify on Etherscan.

Instead I created a new project locally and installed OpenZeppelin Contracts and Truffle (as truffle-flattener needs Truffle) to flatten locally.

npm i @openzeppelin/contracts
npm i truffle

Token.sol

I converted the imports to use the installed OpenZeppelin Contracts (the version needs to match what is used by the version imported by Remix.

pragma solidity ^0.5.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Detailed.sol";

contract Token is ERC20, ERC20Detailed {

    constructor () public ERC20Detailed("Token", "TKN", 18) {
        _mint(msg.sender, 1000000 * (10 ** uint256(decimals())));
    }
}

Flatten

I used truffle-flattener to create a flattened version of the contract

$ npx truffle-flattener ./contracts/Token.sol > ./contracts/Token_Flat.sol

Verify

I verified the contract on Etherscan as a single flat file, with compiler 0.5.16 and no optimization and it verified successfully.
Note: I didn’t have any constructor parameters in this example.

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