Add ERC721ALowCap + tests

contracts/ERC721A.sol

@@ -106,7 +106,7 @@ contract ERC721A is Context, ERC165, IERC721, IERC721Metadata {
         // Counter underflow is impossible as _burnCounter cannot be incremented
         // more than _currentIndex times
         unchecked {
-            return _currentIndex - _burnCounter;    
+            return _currentIndex - _burnCounter;
         }
     }
 
@@ -175,8 +175,8 @@ contract ERC721A is Context, ERC165, IERC721, IERC721Metadata {
                     if (ownership.addr != address(0)) {
                         return ownership;
                     }
-                    // Invariant: 
-                    // There will always be an ownership that has an address and is not burned 
+                    // Invariant:
+                    // There will always be an ownership that has an address and is not burned
                     // before an ownership that does not have an address and is not burned.
                     // Hence, curr will not underflow.
                     while (true) {
@@ -493,7 +493,7 @@ contract ERC721A is Context, ERC165, IERC721, IERC721Metadata {
         _afterTokenTransfers(prevOwnership.addr, address(0), tokenId, 1);
 
         // Overflow not possible, as _burnCounter cannot be exceed _currentIndex times.
-        unchecked { 
+        unchecked {
             _burnCounter++;
         }
     }

contracts/extensions/ERC721ALowCap.sol

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: MIT
+// Creator: Chiru Labs
+
+pragma solidity ^0.8.4;
+
+import '../ERC721A.sol';
+
+/**
+ * @title ERC721A Low Cap
+ * @dev ERC721A Helper functions for Low Cap (<= 10,000) totalSupply.
+ */
+abstract contract ERC721ALowCap is ERC721A {
+
+    /**
+     * @dev Returns the tokenIds of the address. O(totalSupply) in complexity.
+     */
+    function tokensOfOwner(address owner) public view returns (uint256[] memory) {
+        uint256 holdingAmount = balanceOf(owner);
+        uint256 currSupply    = _currentIndex;
+        uint256 tokenIdsIdx;
+        address currOwnershipAddr;
+
+        uint256[] memory list = new uint256[](holdingAmount);
+
+        unchecked {
+            for (uint256 i; i < currSupply; i++) {
+                TokenOwnership memory ownership = _ownerships[i];
+
+                if (ownership.burned) {
+                    continue;
+                }
+
+                // Find out who owns this sequence
+                if (ownership.addr != address(0)) {
+                    currOwnershipAddr = ownership.addr;
+                }
+
+                // Append tokens the last found owner owns in the sequence
+                if (currOwnershipAddr == owner) {
+                    list[tokenIdsIdx++] = i;
+                }
+
+                // All tokens have been found, we don't need to keep searching
+                if(tokenIdsIdx == holdingAmount) {
+                    break;
+                }
+            }
+        }
+
+        return list;
+    }
+}

contracts/mocks/ERC721ALowCap.sol

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: MIT
+// Creators: Chiru Labs
+
+pragma solidity ^0.8.4;
+
+import '../extensions/ERC721ALowCap.sol';
+
+contract ERC721ALowCapMock is ERC721ALowCap {
+    constructor(string memory name_, string memory symbol_) ERC721A(name_, symbol_) {}
+
+    function safeMint(address to, uint256 quantity) public {
+        _safeMint(to, quantity);
+    }
+}

projects.md

@@ -31,4 +31,4 @@ Here are a list of projects that have or will be implementing ERC721A as part of
 - Anim Ape | [Etherscan](https://etherscan.io/address/0xc4f44b646353b1a07053ebc939954f62d35c80b8) | [Twitter](https://twitter.com/Mysthereum_NFT)
 - [Capsule Machine NFT](https://www.capsulemachinenft.com/) | [Etherscan](https://etherscan.io/address/0xc19ced6633f0da7cef642b7a3f6b3ff0bb2465c0) | [Twitter](https://twitter.com/_capsulemachine) 
 - [Mister Otter River Club](https://morc.vercel.app/) | [Etherscan](https://etherscan.io/address/0xa8c724a829a48f551950a783c6ec50e728725026) | [Twitter](https://twitter.com/misterotternft) 
-- [Tasty Bones NFT](https://tastybones.xyz/) | [Etherscan](https://etherscan.io/address/0x1b79c7832ed9358E024F9e46E9c8b6f56633691B) | [Twitter](https://twitter.com/tastybonesnft) 
+- [Tasty Bones NFT](https://tastybones.xyz/) | [Etherscan](https://etherscan.io/address/0x1b79c7832ed9358E024F9e46E9c8b6f56633691B) | [Twitter](https://twitter.com/tastybonesnft) 

test/extensions/ERC721ALowCap.test.js

@@ -0,0 +1,58 @@
+const { expect } = require('chai');
+
+describe('ERC721ALowCap', function () {
+  beforeEach(async function () {
+    this.ERC721ALowCap = await ethers.getContractFactory('ERC721ALowCapMock');
+    this.token = await this.ERC721ALowCap.deploy('Azuki', 'AZUKI');
+    await this.token.deployed();
+  });
+
+  context('with minted tokens', async function() {
+    beforeEach(async function () {
+        const [owner, addr1, addr2, addr3, addr4] = await ethers.getSigners();
+        this.owner = owner;
+        this.addr1 = addr1;
+        this.addr2 = addr2;
+        this.addr3 = addr3;
+        this.addr4 = addr4;
+        await this.token['safeMint(address,uint256)'](addr1.address, 1);
+        await this.token['safeMint(address,uint256)'](addr2.address, 2);
+        await this.token['safeMint(address,uint256)'](addr3.address, 3);
+    });
+
+    describe('tokensOfOwner', async function() {
+        it('returns the correct token ids', async function() {
+            const expected_results = [
+                // Address 1 -- Single token
+                { owner: this.addr1, tokens : [0] },
+                // Address 3 -- Multiple tokens
+                { owner: this.addr3, tokens : [3,4,5] },
+                // Address 4 -- No tokens
+                { owner: this.addr4, tokens : [] }
+            ];
+
+            for(const expected_result of expected_results) {
+                const bn_tokens = await this.token['tokensOfOwner(address)'](expected_result.owner.address);
+                expect(bn_tokens.map(bn => bn.toNumber())).to.eql(expected_result.tokens);
+            }
+        });
+
+        it('returns the correct token ids after a transfer interferes with the normal logic', async function() {
+            // Owner of 6,7,8
+            await this.token['safeMint(address,uint256)'](this.owner.address, 3);
+
+            // Break sequential order
+            await this.token['transferFrom(address,address,uint256)'](this.owner.address, this.addr4.address, 7);
+
+            // Load balances
+            const owner_bn_tokens = await this.token['tokensOfOwner(address)'](this.owner.address);
+            const addr4_bn_tokens = await this.token['tokensOfOwner(address)'](this.addr4.address);
+
+            // Verify the function can still read the correct token ids
+            expect(owner_bn_tokens.map(bn => bn.toNumber())).to.eql([6,8]);
+            expect(addr4_bn_tokens.map(bn => bn.toNumber())).to.eql([7]);
+        });
+    });
+  });
+
+});