Allow configuration of worst case buy execution weight

[girazoki]

Adds worst_case_buy_execution to the Config trait of pallet-xcm-benchmarks with a default implementation that mimics the code that existed previous to this PR.

Rationale: not allowing to set the WeightLimit and the FeeAsset might mean that we dont benchmark the worst case, as with WeightLimit::Unlimited the Trader does not even execute:

polkadot-sdk/polkadot/xcm/xcm-executor/src/lib.rs

Line 833 in c01dbeb

if let Some(weight) = Option::<Weight>::from(weight_limit) {

The new configurable function allows projects to customize the parameters with which the benchmark is run to make sure they account for the worst-case scenario

This is very likely the case of the assethub system chain, with several traders being analyzed and possibly several reads being made:

polkadot-sdk/cumulus/parachains/runtimes/assets/asset-hub-rococo/src/xcm_config.rs

Line 403 in 38d2fa8

cumulus_primitives_utility::TakeFirstAssetTrader<

[girazoki]

CC I am re-opening this #2962. I think it is still valid as right now the buy_execution instruction is being benchmarked with the (Here) asset, which might not include the worst case.

CC @bkchr sorry for not answering before on the closed PR, I somehow missed it

[girazoki]

I remember back in that PR there were a couple of things that needed to be analyzed:

• do we want a default impl for the new helper?
• what is the worst case for assethub? (in which case, I can add it)

[girazoki]

CC @RomarQ

[acatangiu]

cc @franciscoaguirre @bkontur

[girazoki]

Any opinion on this?

[bkontur]

I would not add here default, we want runtimes to set the worst case:

Suggested change

	/// By default returns ((AssetId(Here.into()), 100_000_000u128), Unlimited)
	fn worst_case_buy_execution() -> Result<(Asset, WeightLimit), BenchmarkError> {
	Ok(((AssetId(Junctions::Here.into()), 100_000_000u128).into(), WeightLimit::Unlimited))
	}
	fn worst_case_buy_execution() -> Result<(Asset, WeightLimit), BenchmarkError>;

Just thinking about fn fee_asset() which is supposed to do the same for PayFees,
maybe we could have something like fn worst_case_for_trader() and use it for PayFees and BuyExecution benchmarks.

[franciscoaguirre]

Suggested change

	- name: pallet-xcm-benchmarks
	- name: pallet-xcm-benchmarks
	- bump: major

It's major since you're adding a function with no default.

[acatangiu]

well.. shit! how are we gonna backport then?

I guess we'll have to limit "backport" to just 2503 which hasn't been published yet

[acatangiu]

ah, nevermind, that's fine, we don't really need to backport this too far back