Implement pallet-assets-freezer

[pandres95]

Closes #3342

cc/ @liamaharon

TODO:

• Improve docs.
• Define public interface (See [Assets] Implement fungibles::freeze::Mutate #3342).
  In case we define public calls to the pallet implementation:
  • Implement public calls.
  • Benchmarks.

polkadot address: 12gMhxHw8QjEwLQvnqsmMVY1z5gFa54vND74aMUbhhwN6mJR

[liamaharon]

Pallet extension generally looking really good!

pallet-assets also needs to be modified to allow attaching it, let me know if it's clear enough from Gav's PR how to could do that or if you need some pointers.

[muharem]

can you tell please why two separate types?

[pandres95]

This follows the logic present in pallet-balances:

polkadot-sdk/substrate/frame/balances/src/lib.rs

Line 250 in 0d71753

type RuntimeFreezeReason: VariantCount;

This is used to constraint the maximum amount of freezes to the count of variants in RuntimeFreezeReason on the integrity test, but allowing the implementor of the pallet to use any other type as freeze identifier in case that's needed by the runtime dev.

[liamaharon]

@muharem I was also curious and asked in Element but no one answered.

My best guess is it's to allow constraining the FreezeReasons allowed to be used in the pallet?

[muharem]

Lets imagine FreezeIdentifier is some non enum type, u32 for example. The overarching freeze reason in this case same - u32. The varian count some const u32 number.
So I would imagine this as

trat Config {
    /// The overarching freeze reason.
    type RuntimeFreezeReason: Parameter + Member + MaxEncodedLen + Copy;
    /// Ax number of freezes possible for a single asset account.
    type MaxFreezes: Get<u32>;
}

where any type that implements VariantCount, implements Get<u32> by default via generic impl.

[muharem]

there is actually an adapter VariantCountOf

[pandres95]

Good catch! In pallet-balances, the struct VariantCountOf is used to constraint the limit of Holds, like this:

polkadot-sdk/substrate/frame/balances/src/lib.rs

Lines 476 to 485 in 0d71753

	pub type Holds<T: Config<I>, I: 'static = ()> = StorageMap<
	_,
	Blake2_128Concat,
	T::AccountId,
	BoundedVec<
	IdAmount<T::RuntimeHoldReason, T::Balance>,
	VariantCountOf<T::RuntimeHoldReason>,
	>,
	ValueQuery,
	>;

This approach works in such a way there's no need to test for integrity, removes the need for a MaxHolds, and the ambiguity between RuntimeFreezeReason and FreezeIdentifier. I can apply the same strategy for RuntimeFreezeReason in pallet-assets-freezer.

Open question: considering a freeze reason can be of type RuntimeFreezeReason or any open-ended type that implements VariantCount, should it really be named Runtime in the type?

Note: I also suggest opening an issue to consider whether to standardize this approach to replace FreezeIdentifier/MaxFreezes in pallet-balances in favour of using RuntimeFreezeReason as the freezes Identifier there. Noticeably, for a potentially future implementation of fungibles::hold in pallet-assets either via a pallet extension, or via a direct implementation of those traits. would be good to apply the same approach.

[pandres95]

@muharem just removed FreezeIdentifier in favour of RuntimeFreezeReason as an unambiguous type for identifying freezes on the pallet. Left a comment above to explain the decision, and proposed some other questions and follow-up steps.

[liamaharon]

/tip medium

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[Polkadot-Forum]

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[muharem]

@pandres95 can you please resolve the conflicts and merge the master. we merge this after

[pandres95]

Done @muharem

[muharem]

@pandres95 can you check failing check-umbrella CI, it's marked as required

[pandres95]

@muharem fixed

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

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