How can I link library and contract in one file? - solidity

Question

I am writing smart contract in solidity with hardhat and facing error like missing links for the following libraries.
I think I should do something with sample-nft-test.js, but I don't have any idea what to do.
Does any body know how to solve the problem?
% bin/npm-install
% bin/test
SampleNft
1) "before each" hook for "should be able to return token name by token id"
0 passing (2s)
1 failing
1) SampleNft
"before each" hook for "should be able to return token name by token id":
NomicLabsHardhatPluginError: The contract SampleNft is missing links for the following libraries:
* contracts/SampleNft.sol:TokenTrait
Learn more about linking contracts at https://hardhat.org/plugins/nomiclabs-hardhat-ethers.html#library-linking
at collectLibrariesAndLink (node_modules/#nomiclabs/hardhat-ethers/src/internal/helpers.ts:258:11)
at getContractFactoryFromArtifact (node_modules/#nomiclabs/hardhat-ethers/src/internal/helpers.ts:149:32)
at getContractFactory (node_modules/#nomiclabs/hardhat-ethers/src/internal/helpers.ts:93:12)
at Context.<anonymous> (test/sample-nft-test.js:13:29)
Source codes to reproduce the error
ArakakiEth/SampleNft
sample-nft-test.js
const {
expect,
} = require("chai");
const {
ethers,
} = require("hardhat");
describe("SampleNft", () => {
beforeEach(async () => {
signers = await ethers.getSigners();
const contractFactory = await ethers.getContractFactory("SampleNft", {
signer: signers[0],
});
contract = await contractFactory.deploy();
});
it("should be able to return token name by token id", async () => {
await contract.deployed();
await contract.getName();
});
});
SampleNft.sol
// SPDX-License-Identifier: MIT
pragma solidity 0.8.4;
struct Token {
string name;
}
library TokenTrait {
function getName(Token memory token) external pure returns (string memory) {
return token.name;
}
}
contract SampleNft {
using TokenTrait for Token;
uint tokenId;
mapping(uint => Token) private _tokenIdTokenMap;
constructor() {
tokenId = 0;
}
function mint() external {
Token memory token = Token("First Token");
_tokenIdTokenMap[tokenId] = token;
}
function getName() external view returns (string memory) {
Token memory token = _tokenIdTokenMap[tokenId];
return token.getName();
}
}

Answer 1

library TokenTrait {
function getName(Token memory token) external pure returns (string memory) {
return token.name;
}
}
You set the visibility of the function as external.
In this case, you have to deploy the library and then need to specify a link for the library in contract deployment.
The way to fix your issue is to make the function visibility internal.

Answer 2

The library link should be added when deploying contract.
Please replace with the following code for beforeEach part
beforeEach(async () => {
signers = await ethers.getSigners();
const Lib = await ethers.getContractFactory("TokenTrait");
const lib = await Lib.deploy();
await lib.deployed();
const contractFactory = await ethers.getContractFactory("SampleNft", {
signer: signers[0],
libraries: {
TokenTrait: lib.address,
},
});
contract = await contractFactory.deploy();
});