Account type

[turbolent]

The goal of this proposal is to improve how Cadence provides access to accounts.

The proposed API aims to make account access simpler and safer, by enabling and encouraging the principle of least authority (PoLA) for account access.

This FLIP is based on previous discussion in https://forum.onflow.org/t/super-user-account/4088

[bjartek]

What type will an account we in a prepare statement have?

[turbolent]

@bjartek As described in the "Expose Account Access Through References" section, account values will be only exposed through references, i.e. &Account. The Examples section shows an example.

[austinkline]

Thanks for putting this together @turbolent! My main concern as of now is how an AuthAccount stored in a struct/resource would be migrated. For instance, hybrid custody will need to store an AuthAccount capability in a resource which helps manage access for a parent to get to a child account. Since we're having to add this to a type definition, current type restrictions on contract upgrades would prevent us from migrating to this a new set of interfaces

Any ideas how we can get around that issue?

[turbolent]

@austinkline I clarified in the last commit, 002924e, how a &AuthAccount static type (e.g. used in a Capability), would be migrated.

[austinkline]

Adding another thought as I work through some other hybrid custody related items, what happens if someone has already named an interface or struct of theirs Account in an existing contract?

[turbolent]

@austinkline

What happens if someone has already named an interface or struct of theirs Account in an existing contract

That would lead to an type-checking error where the Account type is declared.

A quick cursory search in https://github.com/bluesign/flow-mainnet-contracts shows that there are currently no such types on Mainnet (yet).

[austinkline]

@austinkline

What happens if someone has already named an interface or struct of theirs Account in an existing contract

That would lead to an type-checking error where the Account type is declared.

A quick cursory search in https://github.com/bluesign/flow-mainnet-contracts shows that there are currently no such types on Mainnet (yet).

Got it, checking for what's out there was my next question. Sounds like only HybridCustody is an issue (we have an Account type in testnet). I'll go ahead and change it tomorrow just to be safe.

[bjartek]

I think the change is good, but i fear the cost of migration here aswell. Is it even possible to do in all cases if we cannot change the type of a field?

[turbolent]

I just realized that we'll also need to rethink getAuthAccount.

Maybe add a type parameter, so any entitled &Account reference can be "summoned"? For example, getAuthAccount<auth(Storage) &Account>(0x1).

We could also "merge" getAuthAccount into getAccount, and have a different type parameter depending on environment, e.g. "hardcode" to &Account in transactions and allow any &Account subtype in scripts.

[turbolent]

@bjartek we'll likely need to somehow allow code to be upgraded in ways that the checker currently rejects, but are actually safe, e.g. here, the name just changes, the underlying value will still be the same (and is actually not storable)

[turbolent]

BTW, there has been an ongoing discussion about naming of entitlements in another FLIP introducing built-in entitlements: https://github.com/onflow/flips/pull/86#discussion_r1192703132

[turbolent]

Some issues I ran into while starting the implementation of this FLIP:

• All contracts have a a predeclared field account, which currently has the type AuthAccount.

  How should we replace this?

  There is intentionally no direct replacement for AuthAccount, so all we can do is to "fully entitle" it as auth(Storage, Contracts, Keys, Inbox, Capabilities) &Account.

• The constructor AuthAccount will also need to change.

  • It should probably be renamed to just Account?
  • Its payer parameter currently has type AuthAccount. Payment at least requires access to storage, so maybe require the Storage entitlement?

  The fine-grained BorrowValue entitlement would probably also suffice, so maybe the entitlement set should be BorrowValue | Storage? cc @dsainati1

[dsainati1]

All contracts have a a predeclared field account, which currently has the type AuthAccount. How should we replace this?

IMO it makes the most sense to just add the fully entitled type here auth(Storage, Contracts, Keys, Inbox, Capabilities) &Account. It's verbose, but users will rarely have to write the full type, and I don't think we should add anything new to the language just for this case.

The fine-grained BorrowValue entitlement would probably also suffice, so maybe the entitlement set should be BorrowValue | Storage?

This makes sense to me.

[turbolent]

Approved in the Cadence Language Design Meeting 🎉