ERC721: static call for ownerOf function

In the ERC721 contract, the ownerOf function is defined as virtual which allows implementations to change this function.

But invocations of this function do NOT call with virtual dispatch (i.e. they use ERC721.ownerOf).

This creates the possibility somebody will override it and it will stop working.

Proposed solutions:

1. Remove virtual—because the ownership is tightly coupled with other implementation details. This is a “breaking change”, whatever, file this under “Will say’s it’s okay”.
2. Use virtual dispatch (s/ERC721\.//g)—this might be inconsistent and confusing

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P.S., in the past, other ERC721 functions were called without virtual dispatch and it created a security problem risk. This affects past versions of OZC. I’m not sure if those versions are still supported (see https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2759). I have seen an implementation in the wild that is vulnerable as a result of this.

[frangio]

Closing this issue for reasons explained in my previous comment: “The burden of guaranteeing internal consistency [when ownerOf is overriden] is moved to the developer who wishes to override in these niche cases.”

The specific case of isApprovedForAll in Contracts 3.x is tracked in https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2792.

[matthiasgeihs]

Thanks @frangio for pointing out ERC721Consecutive. That was exactly what I needed. (Looks like you have included the necessary modification to ERC721 in https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3311.)