pallet-balances: Fix inactive funds migration

[bkchr]

Fixes the inactive funds migration. It was missing to set the storage_version attribute for the Pallet struct. Besides that it also removes the old StorageVersion representation and adds support for instances of pallet-balances.

PR that added the migration: #12813

[joepetrowski]

Does the migration or the new pallet get applied first? Because in the pallet you set the storage version to 1, so if that applies first then IIUC this migration won't actually run.

/// The current storage version.
const STORAGE_VERSION: frame_support::traits::StorageVersion =
	frame_support::traits::StorageVersion::new(1);

[muharem]

On chain version will return 0, at this point this storage item even does not exist.

here the trait

substrate/frame/support/src/traits/metadata.rs

Line 242 in a1d014d

fn on_chain_storage_version() -> StorageVersion;

here the impl

substrate/frame/support/src/dispatch.rs

Line 2518 in a1d014d

impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::traits::GetStorageVersion

and below here in the migration you can see where we updating on chain storage version
https://github.com/paritytech/substrate/pull/12840/files#diff-d3a8ee05060d4cc1bb98df686418ec5aeba54698bd793a46c9095dde576eaa77R41

[bkchr]

The storage version is only set on genesis to the "current version" (aka the version you set in the code). After genesis, you need to bump the version "manually".

[joepetrowski]

On chain version will return 0, at this point this storage item even does not exist.

Maybe I don't understand, because it looks like to me that it is being initialized to 1, so it would exist:
https://github.com/paritytech/substrate/pull/12840/files#diff-7f35e750129ddf17862e61be2ce506a120ac7d4de151633d2c026525130bba7dR251

[muharem]

@joepetrowski that constant, is not persisted anywhere by frame, its only returned by on_chain_storage_version
here

substrate/frame/support/src/dispatch.rs

Line 2522 in a1d014d

$( $storage_version )*

[muharem]

On chain version will return 0, at this point this storage item even does not exist.

here the trait

substrate/frame/support/src/traits/metadata.rs

Line 242 in a1d014d

fn on_chain_storage_version() -> StorageVersion;

here the impl

substrate/frame/support/src/dispatch.rs

Line 2518 in a1d014d

impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::traits::GetStorageVersion

and below here in the migration you can see where we updating on chain storage version
https://github.com/paritytech/substrate/pull/12840/files#diff-d3a8ee05060d4cc1bb98df686418ec5aeba54698bd793a46c9095dde576eaa77R41

[joepetrowski]

I still don't entirely understand the storage version macro, but the other logic in the PR looks correct to me.