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Branislav Kontur
bb8ddc46c1
I started this investigation/issue based on @liamaharon question [here](https://github.com/paritytech/polkadot-sdk/pull/1801#discussion_r1410452499). ## Problem The `pallet_balances` integrity test should correctly detect that the runtime has correct distinct `HoldReasons` variant count. I assume the same situation exists for RuntimeFreezeReason. It is not a critical problem, if we set `MaxHolds` with a sufficiently large value, everything should be ok. However, in this case, the integrity_test check becomes less useful. **Situation for "any" runtime:** - `HoldReason` enums from different pallets: ```rust /// from pallet_nis #[pallet::composite_enum] pub enum HoldReason { NftReceipt, } /// from pallet_preimage #[pallet::composite_enum] pub enum HoldReason { Preimage, } // from pallet_state-trie-migration #[pallet::composite_enum] pub enum HoldReason { SlashForContinueMigrate, SlashForMigrateCustomTop, SlashForMigrateCustomChild, } ``` - generated `RuntimeHoldReason` enum looks like: ```rust pub enum RuntimeHoldReason { #[codec(index = 32u8)] Preimage(pallet_preimage::HoldReason), #[codec(index = 38u8)] Nis(pallet_nis::HoldReason), #[codec(index = 42u8)] StateTrieMigration(pallet_state_trie_migration::HoldReason), } ``` - composite enum `RuntimeHoldReason` variant count is detected as `3` - we set `type MaxHolds = ConstU32<3>` - `pallet_balances::integrity_test` is ok with `3`(at least 3) However, the real problem can occur in a live runtime where some functionality might stop working. This is due to a total of 5 distinct hold reasons (for pallets with multi-instance support, it is even more), and not all of them can be used because of an incorrect `MaxHolds`, which is deemed acceptable according to the `integrity_test`: ``` // pseudo-code - if we try to call all of these: T::Currency::hold(&pallet_nis::HoldReason::NftReceipt.into(), &nft_owner, deposit)?; T::Currency::hold(&pallet_preimage::HoldReason::Preimage.into(), &nft_owner, deposit)?; T::Currency::hold(&pallet_state_trie_migration::HoldReason::SlashForContinueMigrate.into(), &nft_owner, deposit)?; // With `type MaxHolds = ConstU32<3>` these two will fail T::Currency::hold(&pallet_state_trie_migration::HoldReason::SlashForMigrateCustomTop.into(), &nft_owner, deposit)?; T::Currency::hold(&pallet_state_trie_migration::HoldReason::SlashForMigrateCustomChild.into(), &nft_owner, deposit)?; ``` ## Solutions A macro `#[pallet::*]` expansion is extended of `VariantCount` implementation for the `#[pallet::composite_enum]` enum type. This expansion generates the `VariantCount` implementation for pallets' `HoldReason`, `FreezeReason`, `LockId`, and `SlashReason`. Enum variants must be plain enum values without fields to ensure a deterministic count. The composite runtime enum, `RuntimeHoldReason` and `RuntimeFreezeReason`, now sets `VariantCount::VARIANT_COUNT` as the sum of pallets' enum `VariantCount::VARIANT_COUNT`: ```rust #[frame_support::pallet(dev_mode)] mod module_single_instance { #[pallet::composite_enum] pub enum HoldReason { ModuleSingleInstanceReason1, ModuleSingleInstanceReason2, } ... } #[frame_support::pallet(dev_mode)] mod module_multi_instance { #[pallet::composite_enum] pub enum HoldReason<I: 'static = ()> { ModuleMultiInstanceReason1, ModuleMultiInstanceReason2, ModuleMultiInstanceReason3, } ... } impl self::sp_api_hidden_includes_construct_runtime::hidden_include::traits::VariantCount for RuntimeHoldReason { const VARIANT_COUNT: u32 = 0 + module_single_instance::HoldReason::VARIANT_COUNT + module_multi_instance::HoldReason::<module_multi_instance::Instance1>::VARIANT_COUNT + module_multi_instance::HoldReason::<module_multi_instance::Instance2>::VARIANT_COUNT + module_multi_instance::HoldReason::<module_multi_instance::Instance3>::VARIANT_COUNT; } ``` In addition, `MaxHolds` is removed (as suggested [here](https://github.com/paritytech/polkadot-sdk/pull/2657#discussion_r1443324573)) from `pallet_balances`, and its `Holds` are now bounded to `RuntimeHoldReason::VARIANT_COUNT`. Therefore, there is no need to let the runtime specify `MaxHolds`. ## For reviewers Relevant changes can be found here: - `substrate/frame/support/procedural/src/lib.rs` - `substrate/frame/support/procedural/src/pallet/parse/composite.rs` - `substrate/frame/support/procedural/src/pallet/expand/composite.rs` - `substrate/frame/support/procedural/src/construct_runtime/expand/composite_helper.rs` - `substrate/frame/support/procedural/src/construct_runtime/expand/hold_reason.rs` - `substrate/frame/support/procedural/src/construct_runtime/expand/freeze_reason.rs` - `substrate/frame/support/src/traits/misc.rs` And the rest of the files is just about removed `MaxHolds` from `pallet_balances` ## Next steps Do the same for `MaxFreezes` https://github.com/paritytech/polkadot-sdk/issues/2997. --------- Co-authored-by: command-bot <> Co-authored-by: Bastian Köcher <git@kchr.de> Co-authored-by: Dónal Murray <donal.murray@parity.io> Co-authored-by: gupnik <nikhilgupta.iitk@gmail.com>
FRAME
The FRAME development environment provides modules (called "pallets") and support libraries that you can use, modify, and extend to build the runtime logic to suit the needs of your blockchain.
Documentation
https://docs.substrate.io/reference/frame-pallets/