Generic slashing side-effects

[JuaniRios]

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 @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 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)

[kianenigma]

Someday this can help us/one implement https://github.com/paritytech/polkadot-sdk/issues/339.

[franciscoaguirre]

bot fmt

[command-bot[bot]]

@franciscoaguirre https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7395715 was started for your command "$PIPELINE_SCRIPTS_DIR/commands/fmt/fmt.sh". Check out https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/pipelines?page=1&scope=all&username=group_605_bot to know what else is being executed currently.

Comment bot cancel 4-483b8645-287c-4c87-8f54-ef9967c4660c to cancel this command or bot cancel to cancel all commands in this pull request.

[command-bot[bot]]

@franciscoaguirre Command "$PIPELINE_SCRIPTS_DIR/commands/fmt/fmt.sh" has finished. Result: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7395715 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7395715/artifacts/download.

[JuaniRios]

bot fmt

[command-bot[bot]]

@JuaniRios Requester could not be detected as a member of an allowed organization.

[franciscoaguirre]

bot fmt

[command-bot[bot]]

@franciscoaguirre https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7421120 was started for your command "$PIPELINE_SCRIPTS_DIR/commands/fmt/fmt.sh". Check out https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/pipelines?page=1&scope=all&username=group_605_bot to know what else is being executed currently.

Comment bot cancel 2-df158727-91f6-49d9-84b9-cb7164a6a85e to cancel this command or bot cancel to cancel all commands in this pull request.

[command-bot[bot]]

@franciscoaguirre Command "$PIPELINE_SCRIPTS_DIR/commands/fmt/fmt.sh" has finished. Result: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7421120 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7421120/artifacts/download.

[JuaniRios]

@franciscoaguirre @kianenigma PR is passing the main checks. We only need a call to the fmt bot, and I think that will also fix the umbrella check.

I ran python3 ./scripts/generate-umbrella.py --sdk . --version 0.1.0 for the umbrella fix, is that the right command?