Repository: paritytech/substrate
File: frame/support/src/migrations.rs (Rust)

Code before:
	weights::{RuntimeDbWeight, Weight},
};

/// Trait used by [`migrate_from_pallet_version_to_storage_version`] to do the actual migration.
pub trait PalletVersionToStorageVersionHelper {
	fn migrate(db_weight: &RuntimeDbWeight) -> Weight;
}

impl<T: GetStorageVersion + PalletInfoAccess> PalletVersionToStorageVersionHelper for T {
	fn migrate(db_weight: &RuntimeDbWeight) -> Weight {
		const PALLET_VERSION_STORAGE_KEY_POSTFIX: &[u8] = b":__PALLET_VERSION__:";

		fn pallet_version_key(name: &str) -> [u8; 32] {
			crate::storage::storage_prefix(name.as_bytes(), PALLET_VERSION_STORAGE_KEY_POSTFIX)
		}

		sp_io::storage::clear(&pallet_version_key(<T as PalletInfoAccess>::name()));

		let version = <T as GetStorageVersion>::current_storage_version();
		version.put::<T>();

		db_weight.writes(2)
	}
}

#[impl_trait_for_tuples::impl_for_tuples(100)]
impl PalletVersionToStorageVersionHelper for T {
	fn migrate(db_weight: &RuntimeDbWeight) -> Weight {
		let mut weight: Weight = 0;

		for_tuples!( #( weight = weight.saturating_add(T::migrate(db_weight)); )* );

		weight
	}
}

/// Migrate from the `PalletVersion` struct to the new
/// [`StorageVersion`](crate::traits::StorageVersion) struct.
///
/// This will remove all `PalletVersion's` from the state and insert the current storage version.
pub fn migrate_from_pallet_version_to_storage_version<
	Pallets: PalletVersionToStorageVersionHelper,
>(
	db_weight: &RuntimeDbWeight,
) -> Weight {
	Pallets::migrate(db_weight)
}


Review comment (suggestion):
```suggestion
#[cfg_attr(all(not(feature = "tuples-96"), not(feature = "tuples-128")), impl_for_tuples(64))]
#[cfg_attr(all(feature = "tuples-96", not(feature = "tuples-128")), impl_for_tuples(96))]
#[cfg_attr(feature = "tuples-128", impl_for_tuples(128))]
```

Code after:
	weights::{RuntimeDbWeight, Weight},
};
use impl_trait_for_tuples::impl_for_tuples;

/// Trait used by [`migrate_from_pallet_version_to_storage_version`] to do the actual migration.
pub trait PalletVersionToStorageVersionHelper {
	fn migrate(db_weight: &RuntimeDbWeight) -> Weight;
}

impl<T: GetStorageVersion + PalletInfoAccess> PalletVersionToStorageVersionHelper for T {
	fn migrate(db_weight: &RuntimeDbWeight) -> Weight {
		const PALLET_VERSION_STORAGE_KEY_POSTFIX: &[u8] = b":__PALLET_VERSION__:";

		fn pallet_version_key(name: &str) -> [u8; 32] {
			crate::storage::storage_prefix(name.as_bytes(), PALLET_VERSION_STORAGE_KEY_POSTFIX)
		}

		sp_io::storage::clear(&pallet_version_key(<T as PalletInfoAccess>::name()));

		let version = <T as GetStorageVersion>::current_storage_version();
		version.put::<T>();

		db_weight.writes(2)
	}
}

#[cfg_attr(all(not(feature = "tuples-96"), not(feature = "tuples-128")), impl_for_tuples(64))]
#[cfg_attr(all(feature = "tuples-96", not(feature = "tuples-128")), impl_for_tuples(96))]
#[cfg_attr(feature = "tuples-128", impl_for_tuples(128))]
impl PalletVersionToStorageVersionHelper for T {
	fn migrate(db_weight: &RuntimeDbWeight) -> Weight {
		let mut weight: Weight = 0;

		for_tuples!( #( weight = weight.saturating_add(T::migrate(db_weight)); )* );

		weight
	}
}

/// Migrate from the `PalletVersion` struct to the new
/// [`StorageVersion`](crate::traits::StorageVersion) struct.
///
/// This will remove all `PalletVersion's` from the state and insert the current storage version.
pub fn migrate_from_pallet_version_to_storage_version<
	Pallets: PalletVersionToStorageVersionHelper,
>(
	db_weight: &RuntimeDbWeight,
) -> Weight {
	Pallets::migrate(db_weight)
}