Solidityにおけるlibraryの使い方について

前提・実現したいこと

こちらのレポジトリを実験しています。
solcのv0.5.12を推奨されていますが、最新のv0.8.9で開発をしているため、多少コードを書き換えています。

発生している問題・エラーメッセージ

npm run compileSolの部分でエラーとなり、困っています。

% npm run compileSol


> semaphore-contracts@0.0.1 compileSol /Users/username/semaphore-card/semaphore/contracts
> ./scripts/compileSol.sh

Building contracts
Compiling ./sol/IncrementalMerkleTree.sol...
中略
Compiling ./sol/verifier.sol...

{ Error: TypeError: Library functions must be implemented if declared.
  --> /Users/username/semaphore-card/semaphore/contracts/sol/MiMC.sol:28:5:
   |
28 |     function MiMCSponge(uint256 in_xL, uint256 in_xR)
   |     ^ (Relevant source part starts here and spans across multiple lines).

,TypeError: Library functions must be implemented if declared.
  --> sol/MiMC.sol:28:5:
   |
28 |     function MiMCSponge(uint256 in_xL, uint256 in_xR)
   |     ^ (Relevant source part starts here and spans across multiple lines).
    at new ExtendableError (/Users/username/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-error/index.js:7:19)
    at new CompileError (/Users/username/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/compile-error.js:11:5)
    at Promise (/Users/username/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/index.js:81:18)
    at process.runNextTicks [as _tickCallback] (internal/process/task_queues.js:52:5)
    at Function.Module.runMain (internal/modules/cjs/loader.js:880:11)
    at findNodeScript.then.existing (/usr/local/lib/node_modules/npm/node_modules/libnpx/index.js:268:14)
  message:
   'TypeError: Library functions must be implemented if declared.\n  --> /Users/username/semaphore-card/semaphore/contracts/sol/MiMC.sol:28:5:\n   |\n28 |     function MiMCSponge(uint256 in_xL, uint256 in_xR)\n   |     ^ (Relevant source part starts here and spans across multiple lines).\n\n,TypeError: Library functions must be implemented if declared.\n  --> sol/MiMC.sol:28:5:\n   |\n28 |     function MiMCSponge(uint256 in_xL, uint256 in_xR)\n   |     ^ (Relevant source part starts here and spans across multiple lines).\n\u001b[31mCompilation failed. See above.\u001b[39m',
  stack:
   'Error: TypeError: Library functions must be implemented if declared.\n  --> /Users/username/semaphore-card/semaphore/contracts/sol/MiMC.sol:28:5:\n   |\n28 |     function MiMCSponge(uint256 in_xL, uint256 in_xR)\n   |     ^ (Relevant source part starts here and spans across multiple lines).\n\n,TypeError: Library functions must be implemented if declared.\n  --> sol/MiMC.sol:28:5:\n   |\n28 |     function MiMCSponge(uint256 in_xL, uint256 in_xR)\n   |     ^ (Relevant source part starts here and spans across multiple lines).\n    at new ExtendableError (/Users/username/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-error/index.js:7:19)\n    at new CompileError (/Users/username/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/compile-error.js:11:5)\n    at Promise (/Users/username/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/index.js:81:18)\n    at process.runNextTicks [as _tickCallback] (internal/process/task_queues.js:52:5)\n    at Function.Module.runMain (internal/modules/cjs/loader.js:880:11)\n    at findNodeScript.then.existing (/usr/local/lib/node_modules/npm/node_modules/libnpx/index.js:268:14)',
  name: 'CompileError' }
internal/modules/cjs/loader.js:670
    throw err;
    ^

Error: Cannot find module '/Users/username/semaphore-card/semaphore/contracts/build/buildMiMC.js'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:668:15)
    at Function.Module._load (internal/modules/cjs/loader.js:591:27)
    at Function.Module.runMain (internal/modules/cjs/loader.js:877:12)
    at internal/main/run_main_module.js:21:11
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! semaphore-contracts@0.0.1 compileSol: `./scripts/compileSol.sh`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the semaphore-contracts@0.0.1 compileSol script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/username/.npm/_logs/2021-10-07T06_58_24_211Z-debug.log

「MiMC.solで定義してあるlibraryの中のfunctionが使用されていない」とあるのですが、実際にはIncrementalMerkleTree.solというファイルにおいて呼び出されています。

該当のソースコード

MiMC.solはこちらになります。

solidity
1
2//SPDX-License-Identifier: Unlicense
3
4pragma solidity ^0.8.0;
5
6library MiMC {
7    function MiMCSponge(uint256 in_xL, uint256 in_xR)
8        public
9        pure
10        returns (uint256 xL, uint256 xR);
11}
12

呼び出し元のファイルはこちら
IncrementalMerkleTree.sol

solidity
1
2
3//SPDX-License-Identifier: Unlicense
4
5pragma solidity ^0.8.0;
6
7import {SnarkConstants} from "./SnarkConstants.sol";
8import {MiMC} from "./MiMC.sol";
9
10contract IncrementalMerkleTree is SnarkConstants {
11    uint8 internal constant MAX_DEPTH = 32;
12
13    uint8 internal treeLevels;
14
15    uint256 internal nextLeafIndex = 0;
16
17    uint256 public root;
18
19    uint256[MAX_DEPTH] internal zeros;
20
21    uint256[MAX_DEPTH] internal filledSubtrees;
22
23    mapping(uint256 => bool) public rootHistory;
24
25    event LeafInsertion(uint256 indexed leaf, uint256 indexed leafIndex);
26
27    constructor(uint8 _treeLevels, uint256 _zeroValue) {
28        require(
29            _treeLevels > 0 && _treeLevels <= MAX_DEPTH,
30            "IncrementalMerkleTree: _treeLevels must be between 0 and 33"
31        );
32
33
34        treeLevels = _treeLevels;
35
36        zeros[0] = _zeroValue;
37
38        uint256 currentZero = _zeroValue;
39        for (uint8 i = 1; i < _treeLevels; i++) {
40            uint256 hashed = hashLeftRight(currentZero, currentZero);
41            zeros[i] = hashed;
42            filledSubtrees[i] = hashed;
43            currentZero = hashed;
44        }
45
46        root = hashLeftRight(currentZero, currentZero);
47    }
48
49
50    function insertLeaf(uint256 _leaf) internal returns (uint256) {
51        require(
52            _leaf < SNARK_SCALAR_FIELD,
53            "IncrementalMerkleTree: insertLeaf argument must be < SNARK_SCALAR_FIELD"
54        );
55
56        uint256 currentIndex = nextLeafIndex;
57
58        uint256 depth = uint256(treeLevels);
59        require(
60            currentIndex < uint256(2)**depth,
61            "IncrementalMerkleTree: tree is full"
62        );
63
64        uint256 currentLevelHash = _leaf;
65        uint256 left;
66        uint256 right;
67
68        for (uint8 i = 0; i < treeLevels; i++) {
69            if (currentIndex % 2 == 0) {
70                left = currentLevelHash;
71                right = zeros[i];
72
73                filledSubtrees[i] = currentLevelHash;
74            } else {
75                left = filledSubtrees[i];
76                right = currentLevelHash;
77            }
78
79            currentLevelHash = hashLeftRight(left, right);
80
81            currentIndex >>= 1;
82        }
83
84        root = currentLevelHash;
85        rootHistory[root] = true;
86
87        uint256 n = nextLeafIndex;
88        nextLeafIndex += 1;
89
90        emit LeafInsertion(_leaf, n);
91
92        return currentIndex;
93    }
94
95    function hashLeftRight(uint256 _left, uint256 _right)
96        internal
97        pure
98        returns (uint256)
99    {
100
101        uint256 R = _left;
102        uint256 C = 0;
103
104        (R, C) = MiMC.MiMCSponge(R, 0);
105
106        R = addmod(R, _right, SNARK_SCALAR_FIELD);
107        (R, C) = MiMC.MiMCSponge(R, C);
108
109        return R;
110    }
111}
112

試したこと

MiMCSpongeにおいて、returnsがあるにも関わらず、return文が記述されていないのは何故でしょうか？
つまり、次のような書き方になると思います。

library MiMC {
    function MiMCSponge(uint256 in_xL, uint256 in_xR)
        public
        pure
        returns (uint256, uint256)
    {
        return (in_xL, in_xR);
    }
}

実際に実行してみると、別のエラーとなります。

 % npm run compileSol


> semaphore-contracts@0.0.1 compileSol /Users/usernaeme/semaphore-card/semaphore/contracts
> ./scripts/compileSol.sh

Building contracts
Compiling ./sol/IncrementalMerkleTree.sol...
中略
Compiling ./sol/verifier.sol...
Thu, 07 Oct 2021 07:19:49 GMT unhandledRejection: Cannot read property 'children' of undefined
TypeError: Cannot read property 'children' of undefined
    at orderABI (/Users/usernaeme/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/index.js:155:41)
    at Object.keys.forEach (/Users/usernaeme/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/index.js:115:31)
    at Array.forEach (<anonymous>)
    at Object.keys.forEach (/Users/usernaeme/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/index.js:94:33)
    at Array.forEach (<anonymous>)
    at Promise (/Users/usernaeme/semaphore-card/semaphore/contracts/node_modules/etherlime/cli-commands/compiler/etherlime-compile/index.js:92:26)
    at process.runNextTicks [as _tickCallback] (internal/process/task_queues.js:52:5)
    at Function.Module.runMain (internal/modules/cjs/loader.js:880:11)
    at findNodeScript.then.existing (/usr/local/lib/node_modules/npm/node_modules/libnpx/index.js:268:14)

バージョンの違いが原因で書き方が変わったのかと思い調べてみましたが、参考になるようなことはありませんでした。

https://docs.soliditylang.org/en/v0.8.9/contracts.html#libraries

他に見落としてることがあれば、ご享受いただけると幸いです