ERC4626: Sweep residual assets on final withdraw to avoid stranded funds

[viktorking7]

Description

Prevents stranded assets when totalSupply == 0 by sweeping any residual underlying tokens to the current receiver on the last withdraw, and reflecting the swept amount in the Withdraw event.

Direct donations or rounding can leave non-zero totalAssets with zero shares, causing future deposits to mint 0 shares and making assets effectively stuck.

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Latest commit: 2d1ce226cb38fb3f074b55d9c88ce14ec341c6db

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[coderabbitai[bot]]

Walkthrough

The ERC4626 contract's _withdraw method was modified to handle residual asset balances. After burning shares and transferring assets, the implementation now sweeps any remaining asset balance to the receiver when the vault is emptied (when totalSupply() equals zero). The total amount swept is added to withdrawnAssets, and the Withdraw event emission was updated to report withdrawnAssets instead of the original assets parameter to accurately reflect the total amount transferred, including swept residuals. The deposit path remains unchanged.

Possibly related PRs

• OpenZeppelin/openzeppelin-contracts#5970: Both PRs modify the ERC4626 _withdraw flow, with this PR adding post-withdrawal sweeping of residual assets while the other introduces overridable _transferOut for direct transfer operations.

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: sweeping residual assets on final withdraw to prevent stranded funds in ERC4626, which directly matches the implementation in the changeset.
Description check	✅ Passed	The description clearly explains the problem (stranded assets when totalSupply == 0), the solution (sweeping residual tokens), and the motivation (direct donations or rounding), all directly related to the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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• contracts/token/ERC20/extensions/ERC4626.sol (1 hunks)

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🔇 Additional comments (1)

contracts/token/ERC20/extensions/ERC4626.sol (1)

298-308: Great dust-sweep addition

Sweeping the leftover balance once the last shares are burned cleanly fixes the stranded-asset edge case without widening the reentrancy surface, and updating the event to report the actual amount withdrawn keeps downstream accounting intact. Nicely done.

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[Amxx]

I'm worried this would possibly be used by an attacker to extract value that is supposed to be burned.

This change give access to all the rounding error that accumulate through the life of the contract. It also allows recovering the the part of donations that is lost to the offset, possibly negating the effectiveness of the protection.