can add prev_owner/from attributes at transfer_nft and send_nft?

[ALPAC-4]

When owner approve the token and contract execute transfer, we can't know where is the token came from by the logs.

This is really hard to track token transfer. I made an example on terra.

1. User A make approve to transfer the cw721 token to contract B
   https://finder.terra.money/columbus-5/tx/14D4251F41053E7572A740D7FDB1760A2D3FD593870B0D70FB1EDBCA7121F211

2. User C execute the contract B to send it to B
   https://finder.terra.money/columbus-5/tx/AEA9F3EEF1AD4A29644355777BD4157422E55E50130C2D330BC6EC0F4E63F51F

The token transferred to B from A. But there is no information about that at tx of 2.

Because of this Cw20 have transfer_from and send_from.

It is possible to make the attribute that can show the previous owner?

[ALPAC-4]

    fn transfer_nft(
        &self,
        deps: DepsMut,
        env: Env,
        info: MessageInfo,
        recipient: String,
        token_id: String,
    ) -> Result<Response<C>, ContractError> {
        let token = self.tokens.load(deps.storage, &token_id)?;
        let owner = token.owner;
        self._transfer_nft(deps, &env, &info, &recipient, &token_id)?;
        Ok(Response::new()
            .add_attribute("action", "transfer_nft")
            .add_attribute("sender", info.sender)
            .add_attribute("from", owner)
            .add_attribute("recipient", recipient)
            .add_attribute("token_id", token_id))
    }

maybe like this?

[larry0x]

Second this. Contracts receiving the NFT more likely will want to know who's the previous owner instead of who initiated the transfer.

In ERC-721 specs, the Transfer event simply contains from and to attributes. I think CW721 should do the same.

Also Transfer should really be their own events instead of lumped together with other logging info. This makes is much easier for indexers to parse transactions.

[JakeHartnell]

Feel free to make a PR.

[peara]

@shanev @JakeHartnell should we reopen this one? I don't quite understand why previous PR was not approved.
I'd like to understand your view on this first. After that, I can open a new PR.
I want to change sender to the NFT owner, and omit the transaction sender from the event as it can always be found from the transaction data.
This could be a breaking change for some but we have versioning now and indexer can use that to determine the value.