FRAME: Move pallets over to use `fungible` traits

[gavofyork]

• Move over all pallets using Currency to fungible traits:
  • Basic code switch over: pallets should provide a utility for cancelling a lock/reserve and instating a freeze/hold.
  • Staking pallet should use hold instead of lock.
  • Permissionless fee-free dispatchable in all pallets to move over.
  • Mark all Currency traits as deprecated.

Eventually, we will also want to deprecate and remove Balances dispatchables:

• Substitute all usages of Balances dispatchables with fungible API.
• Mark dispatchables as deprecated.
• Remove them (this can only be done once XCM execution from private accounts is safe and enabled).

Pallet migrations needed

Here's a list of pallets, turning this into a tracking issue of the migration process.

• [x] CurrencyAdapter, as per https://github.com/paritytech/polkadot-sdk/issues/1833 https://github.com/paritytech/polkadot-sdk/pull/2292.
• [ ] ./frame/staking/src/pallet/mod.rs type Currency: LockableCurrency
• [ ] ./frame/assets/src/lib.rs @gilescope type Currency: ReservableCurrency<Self::AccountId>;
• [ ] ./frame/elections-phragmen/src/lib.rs type Currency: LockableCurrency<Self::AccountId, Moment = Self::BlockNumber> https://github.com/paritytech/polkadot-sdk/pull/2011
• [ ] ./frame/election-provider-multi-phase/src/lib.rs type Currency: ReservableCurrency<Self::AccountId> + Currency<Self::AccountId>;
• [ ] ./frame/lottery/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1810
• [ ] #1861
• [ ] ./frame/treasury/src/lib.rs type Currency: Currency<Self::AccountId> + ReservableCurrency<Self::AccountId>; @juangirini
• [ ] ./frame/nicks/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1801
• [ ] ./frame/state-trie-migration/src/lib.rs type Currency: Currency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1801
• [ ] ./frame/nfts/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1804
• [ ] ./frame/uniques/src/lib.rs @jsidorenko type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1866
• [x] /frame/nis/src/lib.rs type Currency: FunInspect<Self::AccountId, Balance = Self::CurrencyBalance>
• [ ] ./frame/vesting/src/lib.rs type Currency: LockableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1760
• [x] ./frame/contracts/src/lib.rs @juangirini https://github.com/paritytech/substrate/pull/14020 type Currency: ReservableCurrency<Self::AccountId> // TODO: Move to fungible traits
• [ ] ./frame/identity/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; @juangirini https://github.com/paritytech/polkadot-sdk/pull/2822
• [ ] ./frame/scored-pool/src/lib.rs `type Currency: Currency + ReservableCurrency; #1834
• [ ] ./frame/fast-unstake/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1772
• [ ] ./frame/society/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1853
• [ ] ./frame/multisig/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1782
• [x] ./frame/asset-rate/src/lib.rs type Currency: Inspect<Self::AccountId, Balance = Self::Balance>;
• [x] ./frame/nomination-pools/src/lib.rs @Ank4n type Currency: Currency<Self::AccountId>;
• [ ] ./frame/alliance/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1675
• [x] ./frame/statement/src/lib.rs type Currency: Inspect<Self::AccountId>;
• [ ] ./frame/recovery/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; @juangirini https://github.com/paritytech/polkadot-sdk/pull/1807
• [ ] ./frame/preimage/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/substrate/pull/13666
• [ ] ./frame/conviction-voting/src/lib.rs type Currency: ReservableCurrency<Self::AccountId> https://github.com/paritytech/polkadot-sdk/pull/1821
• [ ] ./frame/proxy/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1837
• [ ] ./frame/indices/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1789
• [x] ./frame/transaction-storage/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1800
• [ ] ./frame/referenda/src/lib.rs type Currency: ReservableCurrency<Self::AccountId>; https://github.com/paritytech/polkadot-sdk/pull/1785
• [ ] bridges/modules/relayers/src/stake_adapter.rs Currency: NamedReservableCurrency<AccountId> (@bkontur working on it)
• [ ] bridges/bin/runtime-common/src/refund_relayer_extension.rs ReservableCurrency (@bkontur working on it)

[shawntabrizi]

I made a comment here, but will bring it here too.

While changing from Currency to Fungible trait, I think you should also update the name of the Associated type.

For example, this is weird to me:

/// Currency type that this works on.
type Currency: FunInspect<Self::AccountId, Balance = Self::CurrencyBalance>
    + FunMutate<Self::AccountId>
    + FunBalanced<Self::AccountId>
    + FunHoldMutate<Self::AccountId, Reason = Self::RuntimeHoldReason>;

Perhaps we should use the name NativeBalance for the native token balance (Balances pallet), and TokenBalance for use of the Assets pallet and stuff.

[bkontur]

We can observe various approaches to this refactoring. I think it does not provide the best developer experience to see the "same" stuff implemented in multiple ways within a single repository:

// 1.
type Currency: Mutate<Self::AccountId> + Balanced<Self::AccountId>;

// 2.
type Currency: frame_support::traits::fungible::Inspect<Self::AccountId>;

// 3.
/// This is kind of unclear `Fn` as Function? or `Fn` as Fungible? What about Fungibles? Fns?
type Currency: FnMutate<Self::AccountId>
            + FnMutateHold<Self::AccountId, Reason = Self::RuntimeHoldReason>
            + FnBalanced<Self::AccountId>;

// 4.
/// Also `Fun` as Function? or `Fun` as Fungible? What about Fungibles? Funs?
type Currency: FunMutate<Self::AccountId>
            + FunMutateHold<Self::AccountId, Reason = Self::RuntimeHoldReason>
            + FunBalanced<Self::AccountId>;

// 5.
type Currency: InspectFungible<Self::AccountId>
            + MutateFungible<Self::AccountId>
            + HoldMutateFungible<Self::AccountId, Reason = Self::RuntimeHoldReason>;

If we reach a consensus, I have no problem completing the refactoring according to the chosen approach (at least for already merged code).

I would vote for //5. as it appears to be the most readable and avoids potential discrepancies between fungible and fungibles in the same context.

// 5.
InspectFungible
MutateFungible
HoldMutateFungible
BalancedFungible

Any thoughts?

[liamaharon]

Yeah I also really dislike 2,3,4. Thanks for this, good that we standardise.

I also don't really like 5. Instead I would suggest

• If we are using only one of fungible or fungibles in the scope, approach 1.
• If we are using both of fungible and fungibles in the scope, just use fungible::Inspect, fungibles::Balanced, etc to differentiate them instead of doing a bunch of as namings.

Imo it's cleaner to differentiate traits using our existing module structure rather than making up a new pattern and writing as everywhere which imo is tedious to implement.

Let me know what you think.

[bkontur]

Yeah I also really dislike 2,3,4. Thanks for this, good that we standardise.

I also don't really like 5. Instead I would suggest

* If we are using only one of `fungible` or `fungibles` in the scope, approach 1.

* If we are using both of `fungible` and `fungibles` in the scope, just use `fungible::Inspect`, `fungibles::Balanced`, etc to differentiate them instead of doing a bunch of `as` namings.

Imo it's cleaner to differentiate traits using our existing module structure rather than making up a new pattern and writing as everywhere which imo is tedious to implement.

Let me know what you think.

cool, I am with you, yes, lets avoid those as, and simplify that, I will prepare PR (probably based on https://github.com/paritytech/polkadot-sdk/pull/1801) and lets see

[Polkadot-Forum]

This issue has been mentioned on Polkadot Forum. There might be relevant details there:

https://forum.polkadot.network/t/polkadot-release-analysis-v1-4-0/5152/1