Generic slashing side-effects (#5623)
# Description ## What? Make it possible for other pallets to implement their own logic when a slash on a balance occurs. ## Why? In the [introduction of holds](https://github.com/paritytech/substrate/pull/12951) @gavofyork said: > Since Holds are designed to be infallibly slashed, this means that any logic using a Freeze must handle the possibility of the frozen amount being reduced, potentially to zero. A permissionless function should be provided in order to allow bookkeeping to be updated in this instance. At Polimec we needed to find a way to reduce the vesting schedules of our users after a slash was made, and after talking to @Kianenigma at the Web3Summit, we realized there was no easy way to implement this with the current traits, so we came up with this solution. ## How? - First we abstract the `done_slash` function of holds::Balanced to it's own trait that any pallet can implement. - Then we add a config type in pallet-balances that accepts a callback tuple of all the pallets that implement this trait. - Finally implement done_slash for pallet-balances such that it calls the config type. ## Integration The default implementation of done_slash is still an empty function, and the new config type of pallet-balances can be set to an empty tuple, so nothing changes by default. ## Review Notes - I suggest to focus on the first commit which contains the main logic changes. - I also have a working implementation of done_slash for pallet_vesting, should I add it to this PR? - If I run `cargo +nightly fmt --all` then I get changes to a lot of unrelated crates, so not sure if I should run it to avoid the fmt failure of the CI - Should I hunt down references to fungible/fungibles documentation and update it accordingly? **Polkadot address:** `15fj1UhQp8Xes7y7LSmDYTy349mXvUwrbNmLaP5tQKBxsQY1` # Checklist * [x] My PR includes a detailed description as outlined in the "Description" and its two subsections above. * [x] My PR follows the [labeling requirements]( https://github.com/paritytech/polkadot-sdk/blob/master/docs/contributor/CONTRIBUTING.md#Process ) of this project (at minimum one label for `T` required) * External contributors: ask maintainers to put the right label on your PR. * [ ] I have made corresponding changes to the documentation (if applicable) --------- Co-authored-by:Kian Paimani <[email protected]> Co-authored-by: command-bot <> Co-authored-by:
Francisco Aguirre <[email protected]>