Add ERC721URIStorage extension

[Amxx]

Fixes #2554

PR Checklist

• Tests
• Documentation
• Changelog entry

[frangio]

It seems the contract was designed as fully compatible with Contracts 3.x, but I thought the only thing we wanted to preserve was the ability to customize the URI per-token, so only _setTokenURI. Defining the base URI through overriding is a better mechanism for gas, and I don't think we lose a significant feature if we remove _setBaseURI.

And I would consider defining tokenURI so that it delegates to super.tokenURI in the fallback case.

I would also remove the public baseURI.

Regarding the name, I was thinking something like ERC721URIStorage?

[frangio]

Are these changes related to the PR? I don't understand why they're here.

[Amxx]

Some ERC721 mocks make all internal functions available, other don't. I wanted to improve consistency by making all the mocks show all the functions.

[sambacha]

Any chance this will be backported? 

Thanks!

[Amxx]

Hello @sambacha,

The ERC721 implementation that is part of previous version of contracts (3.x) does include this by default. We are only adding this as a separate module because this logic was removed from the base ERC721 implementation in 4.0.

What version of contracts are you using, and what exactly do you find missing ?

[superphly]

So, how does one implement this contract without having to mutate the other contracts in the repo? I'm currently developing on this 4.0 branch, but I don't want a mutated copy.

[frangio]

@superphly I'm not sure I understood your question! But this is an example of how you would use this contract:

import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";

contracts MyNFT is ERC721URIStorage {
  constructor() ERC721("Name", "SYM") 
}

It's not necessary to add ERC721 in the inheritance list because it is implied by ERC721URIStorage.

If you have any further questions feel free to ask for help in the OpenZeppelin Forum.