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Implicitly clear ERC721 approval on transfers #3481

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merged 4 commits into from
Jul 4, 2022
Merged

Implicitly clear ERC721 approval on transfers #3481

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b4eb5c7
Implicitly clear approval
AnAllergyToAnalogy Jun 16, 2022
4c19fa9
update tests
Amxx Jun 16, 2022
26190c8
Merge branch 'master' into patch-2
frangio Jul 1, 2022
b7090f7
update changelog and add compatibility warning
frangio Jul 1, 2022
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5 changes: 5 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,11 @@
* `Address`: optimize `functionCall` functions by checking contract size only if there is no returned data. ([#3469](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3469))
* `GovernorCompatibilityBravo`: remove unused `using` statements ([#3506](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3506))
* `ERC20`: optimize `_transfer`, `_mint` and `_burn` by using `unchecked` arithmetic when possible. ([#3513](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3513))
* `ERC721`: optimize transfers by making approval clearing implicit instead of emitting an event. ([#3481](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3481))

### Compatibility Note

ERC-721 integrators that interpret contract state from events should make sure that they implement the clearing of approval that is implicit in every transfer according to the EIP. Previous versions of OpenZeppellin Contracts emitted an explicit `Approval` event even though it was not required by the specification, and this is no longer the case.

## 4.7.0 (2022-06-29)

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2 changes: 1 addition & 1 deletion contracts/token/ERC721/ERC721.sol
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Expand Up @@ -338,7 +338,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
_beforeTokenTransfer(from, to, tokenId);

// Clear approvals from the previous owner
_approve(address(0), tokenId);
delete _tokenApprovals[tokenId];

_balances[from] -= 1;
_balances[to] += 1;
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4 changes: 0 additions & 4 deletions test/token/ERC721/ERC721.behavior.js
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Expand Up @@ -96,10 +96,6 @@ function shouldBehaveLikeERC721 (errorPrefix, owner, newOwner, approved, another
expect(await this.token.getApproved(tokenId)).to.be.equal(ZERO_ADDRESS);
});

it('emits an Approval event', async function () {
expectEvent(receipt, 'Approval', { owner, approved: ZERO_ADDRESS, tokenId: tokenId });
});

it('adjusts owners balances', async function () {
expect(await this.token.balanceOf(owner)).to.be.bignumber.equal('1');
});
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