[standard v2] Remove INFT interface from NonFungibleToken

[SupunS]

Issue To Be Solved

I guess the reason for keeping that was to make the NonFungibleToken backward compatible, and to make the life easier for the migrations.

Now that the migrations and contract update validator support changing the type from NonFungibleToken.INFT to NonFungibleToken.NFT (added in onflow/flow-go#5564), we could remove the old INFT interface, and ask developers to start using the new NFT.

In-fact now it is also unsafe from migrations point of view, to have both the INFT and the NFT around, because it could theoretically cause "type confusion" for certain migrated values. So removing the INFT interface, and requiring people to start using NFT instead seems the best option.

[joshuahannan]

I'm hesitant to make any more breaking changes to the standard because we said that it was finalized. Is this something we really need to do?

[SupunS]

So the problem for the migrations is that developers now have two options to go with (could either use INFT or NFT), and that will create ambiguity for the migrations.

I opened this PR: onflow/cadence#3193, to add a restriction to the contract update validation, such that it will enforce the developers to use the new NFT when updating conformance in their contracts. So removing it here physically would not be required, but people will have to switch to start using the new one when updating their code.

Would that going to be OK? Or do you think we should still let them use the old one?

[SupunS]

Just to be clear, as an alternative solution, we can let people use both INFT and NFT for conformances. But if we take this path, then anyone who wants to change their conformance from the old INFT to the new NFT would not be able to do so.
i.e: converting

flow-nft/contracts/ExampleNFT.cdc

Line 39 in 4c0c684

pub resource NFT: NonFungibleToken.INFT, MetadataViews.Resolver {

to

flow-nft/contracts/ExampleNFT.cdc

Line 25 in 3a595a3

access(all) resource NFT: NonFungibleToken.NFT, ViewResolver.Resolver {

will not be supported. They would have to keep using the NFT: NonFungibleToken.INFT conformance as is.

[turbolent]

Even though this change is not required, it would be great to still get it in.

It would improve the situation for existing code, which currently may and will have to keep using INFT, while new code will likely use NFT. Old code can currently not switch to using NFT. This leaves a confusing situation where some code uses INFT and other code uses NFT. We might want to make this cleaner.

The proposed change, the removal of the INFT type, was already previously agreed on in the FLIP, and it was only re-introduced as a work-around to keep the migration simple.

[joshuahannan]

It isn't about whether or not I agree with the change, it is that we told everyone that the standards were finalized and that we wouldn't be making any more breaking changes to them and I'm trying to figure out if it is okay to go back on that.

[joshuahannan]

After thinking a little bit, I believe it is probably okay. I made the change in supun's branch. Nobody has staged any updates yet, right?

[turbolent]

I guess this issue can be closed now?

[SupunS]

Added in #205