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// Copyright 2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.
// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Substrate. If not, see <http://www.gnu.org/licenses/>.
//! A slashing implementation for NPoS systems.
//!
//! For the purposes of the economic model, it is easiest to think of each validator
//! of a nominator which nominates only its own identity.
//!
//! The act of nomination signals intent to unify economic identity with the validator - to take part in the
//! rewards of a job well done, and to take part in the punishment of a job done badly.
//!
//! There are 3 main difficulties to account for with slashing in NPoS:
//! - A nominator can nominate multiple validators and be slashed via any of them.
//! - Until slashed, stake is reused from era to era. Nominating with N coins for E eras in a row
//! does not mean you have N*E coins to be slashed - you've only ever had N.
//! - Slashable offences can be found after the fact and out of order.
//!
//! The algorithm implemented in this module tries to balance these 3 difficulties.
//!
//! First, we only slash participants for the _maximum_ slash they receive in some time period,
//! rather than the sum. This ensures a protection from overslashing.
//!
//! Second, we do not want the time period (or "span") that the maximum is computed
//! over to last indefinitely. That would allow participants to begin acting with
//! impunity after some point, fearing no further repercussions. For that reason, we
//! automatically "chill" validators and withdraw a nominator's nomination after a slashing event,
//! requiring them to re-enlist voluntarily (acknowledging the slash) and begin a new
//! slashing span.
//!
//! Typically, you will have a single slashing event per slashing span. Only in the case
//! where a validator releases many misbehaviors at once, or goes "back in time" to misbehave in
//! eras that have already passed, would you encounter situations where a slashing span
//! has multiple misbehaviors. However, accounting for such cases is necessary
//! to deter a class of "rage-quit" attacks.
//!
//! Based on research at https://research.web3.foundation/en/latest/polkadot/slashing/npos/
use super::{
EraIndex, Trait, Module, Store, BalanceOf, Exposure, Perbill, SessionInterface,
NegativeImbalanceOf, UnappliedSlash,
};
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use support::{
StorageMap, StorageDoubleMap,
traits::{Currency, OnUnbalanced, Imbalance},
};
use rstd::vec::Vec;
use codec::{Encode, Decode};
/// The proportion of the slashing reward to be paid out on the first slashing detection.
/// This is f_1 in the paper.
const REWARD_F1: Perbill = Perbill::from_percent(50);
/// The index of a slashing span - unique to each stash.
pub(crate) type SpanIndex = u32;
// A range of start..end eras for a slashing span.
#[derive(Encode, Decode)]
#[cfg_attr(test, derive(Debug, PartialEq))]
pub(crate) struct SlashingSpan {
pub(crate) index: SpanIndex,
pub(crate) start: EraIndex,
pub(crate) length: Option<EraIndex>, // the ongoing slashing span has indeterminate length.
}
impl SlashingSpan {
fn contains_era(&self, era: EraIndex) -> bool {
self.start <= era && self.length.map_or(true, |l| self.start + l > era)
}
}
/// An encoding of all of a nominator's slashing spans.
#[derive(Encode, Decode)]
pub struct SlashingSpans {
// the index of the current slashing span of the nominator. different for
// every stash, resets when the account hits free balance 0.
span_index: SpanIndex,
// the start era of the most recent (ongoing) slashing span.
last_start: EraIndex,
// all prior slashing spans start indices, in reverse order (most recent first)
// encoded as offsets relative to the slashing span after it.
prior: Vec<EraIndex>,
}
impl SlashingSpans {
// creates a new record of slashing spans for a stash, starting at the beginning
// of the bonding period, relative to now.
fn new(window_start: EraIndex) -> Self {
SlashingSpans {
span_index: 0,
last_start: window_start,
prior: Vec::new(),
}
}
// update the slashing spans to reflect the start of a new span at the era after `now`
// returns `true` if a new span was started, `false` otherwise. `false` indicates
// that internal state is unchanged.
fn end_span(&mut self, now: EraIndex) -> bool {
let next_start = now + 1;
if next_start <= self.last_start { return false }
let last_length = next_start - self.last_start;
self.prior.insert(0, last_length);
self.last_start = next_start;
self.span_index += 1;
true
}
// an iterator over all slashing spans in _reverse_ order - most recent first.
pub(crate) fn iter(&'_ self) -> impl Iterator<Item = SlashingSpan> + '_ {
let mut last_start = self.last_start;
let mut index = self.span_index;
let last = SlashingSpan { index, start: last_start, length: None };
let prior = self.prior.iter().cloned().map(move |length| {
let start = last_start - length;
last_start = start;
index -= 1;
SlashingSpan { index, start, length: Some(length) }
});
rstd::iter::once(last).chain(prior)
}
/// Yields the era index where the last (current) slashing span started.
pub(crate) fn last_start(&self) -> EraIndex {
self.last_start
}
// prune the slashing spans against a window, whose start era index is given.
//
// If this returns `Some`, then it includes a range start..end of all the span
// indices which were pruned.
fn prune(&mut self, window_start: EraIndex) -> Option<(SpanIndex, SpanIndex)> {
let old_idx = self.iter()
.skip(1) // skip ongoing span.
.position(|span| span.length.map_or(false, |len| span.start + len <= window_start));
let earliest_span_index = self.span_index - self.prior.len() as SpanIndex;
let pruned = match old_idx {
Some(o) => {
self.prior.truncate(o);
let new_earliest = self.span_index - self.prior.len() as SpanIndex;
Some((earliest_span_index, new_earliest))
}
None => None,
};
// readjust the ongoing span, if it started before the beginning of the window.
self.last_start = rstd::cmp::max(self.last_start, window_start);
pruned
}
}
/// A slashing-span record for a particular stash.
#[derive(Encode, Decode, Default)]
pub(crate) struct SpanRecord<Balance> {
slashed: Balance,
paid_out: Balance,
}
impl<Balance> SpanRecord<Balance> {
/// The value of stash balance slashed in this span.
#[cfg(test)]
pub(crate) fn amount_slashed(&self) -> &Balance {
&self.slashed
}
}
/// Parameters for performing a slash.
#[derive(Clone)]
pub(crate) struct SlashParams<'a, T: 'a + Trait> {
/// The stash account being slashed.
pub(crate) stash: &'a T::AccountId,
/// The proportion of the slash.
pub(crate) slash: Perbill,
/// The exposure of the stash and all nominators.
pub(crate) exposure: &'a Exposure<T::AccountId, BalanceOf<T>>,
/// The era where the offence occurred.
pub(crate) slash_era: EraIndex,
/// The first era in the current bonding period.
pub(crate) window_start: EraIndex,
/// The current era.
pub(crate) now: EraIndex,
/// The maximum percentage of a slash that ever gets paid out.
/// This is f_inf in the paper.
pub(crate) reward_proportion: Perbill,
}
/// Computes a slash of a validator and nominators. It returns an unapplied
/// record to be applied at some later point. Slashing metadata is updated in storage,
/// since unapplied records are only rarely intended to be dropped.
///
/// The pending slash record returned does not have initialized reporters. Those have
/// to be set at a higher level, if any.
pub(crate) fn compute_slash<T: Trait>(params: SlashParams<T>)
-> Option<UnappliedSlash<T::AccountId, BalanceOf<T>>>
{
let SlashParams {
stash,
slash,
exposure,
slash_era,
window_start,
now,
reward_proportion,
} = params.clone();
let mut reward_payout = Zero::zero();
let mut val_slashed = Zero::zero();
// is the slash amount here a maximum for the era?
let own_slash = slash * exposure.own;
if slash * exposure.total == Zero::zero() {
// kick out the validator even if they won't be slashed,
// as long as the misbehavior is from their most recent slashing span.
kick_out_if_recent::<T>(params);
return None;
}
let (prior_slash_p, _era_slash) = <Module<T> as Store>::ValidatorSlashInEra::get(
&slash_era,
stash,
).unwrap_or((Perbill::zero(), Zero::zero()));
// compare slash proportions rather than slash values to avoid issues due to rounding
// error.
if slash.deconstruct() > prior_slash_p.deconstruct() {
<Module<T> as Store>::ValidatorSlashInEra::insert(
&slash_era,
stash,
&(slash, own_slash),
);
} else {
// we slash based on the max in era - this new event is not the max,
// so neither the validator or any nominators will need an update.
//
// this does lead to a divergence of our system from the paper, which
// pays out some reward even if the latest report is not max-in-era.
// we opt to avoid the nominator lookups and edits and leave more rewards
// for more drastic misbehavior.
return None;
}
// apply slash to validator.
{
let mut spans = fetch_spans::<T>(
stash,
window_start,
&mut reward_payout,
&mut val_slashed,
reward_proportion,
);
let target_span = spans.compare_and_update_span_slash(
slash_era,
own_slash,
);
if target_span == Some(spans.span_index()) {
// misbehavior occurred within the current slashing span - take appropriate
// actions.
// chill the validator - it misbehaved in the current span and should
// not continue in the next election. also end the slashing span.
spans.end_span(now);
<Module<T>>::chill_stash(stash);
// make sure to disable validator till the end of this session
if T::SessionInterface::disable_validator(stash).unwrap_or(false) {
// force a new era, to select a new validator set
<Module<T>>::ensure_new_era()
}
}
}
let mut nominators_slashed = Vec::new();
reward_payout += slash_nominators::<T>(params, prior_slash_p, &mut nominators_slashed);
Some(UnappliedSlash {
validator: stash.clone(),
own: val_slashed,
others: nominators_slashed,
reporters: Vec::new(),
payout: reward_payout,
})
}
// doesn't apply any slash, but kicks out the validator if the misbehavior is from
// the most recent slashing span.
fn kick_out_if_recent<T: Trait>(
params: SlashParams<T>,
) {
// these are not updated by era-span or end-span.
let mut reward_payout = Zero::zero();
let mut val_slashed = Zero::zero();
let mut spans = fetch_spans::<T>(
params.stash,
params.window_start,
&mut reward_payout,
&mut val_slashed,
params.reward_proportion,
);
if spans.era_span(params.slash_era).map(|s| s.index) == Some(spans.span_index()) {
spans.end_span(params.now);
<Module<T>>::chill_stash(params.stash);
// make sure to disable validator till the end of this session
if T::SessionInterface::disable_validator(params.stash).unwrap_or(false) {
// force a new era, to select a new validator set
<Module<T>>::ensure_new_era()
}
}
}
/// Slash nominators. Accepts general parameters and the prior slash percentage of the validator.
///
/// Returns the amount of reward to pay out.
fn slash_nominators<T: Trait>(
params: SlashParams<T>,
prior_slash_p: Perbill,
nominators_slashed: &mut Vec<(T::AccountId, BalanceOf<T>)>,
) -> BalanceOf<T> {
let SlashParams {
stash: _,
slash,
exposure,
slash_era,
window_start,
now,
reward_proportion,
} = params;
let mut reward_payout = Zero::zero();
nominators_slashed.reserve(exposure.others.len());
for nominator in &exposure.others {
let stash = &nominator.who;
let mut nom_slashed = Zero::zero();
// the era slash of a nominator always grows, if the validator
// had a new max slash for the era.
let era_slash = {
let own_slash_prior = prior_slash_p * nominator.value;
let own_slash_by_validator = slash * nominator.value;
let own_slash_difference = own_slash_by_validator.saturating_sub(own_slash_prior);
let mut era_slash = <Module<T> as Store>::NominatorSlashInEra::get(
&slash_era,
stash,
).unwrap_or(Zero::zero());
era_slash += own_slash_difference;
<Module<T> as Store>::NominatorSlashInEra::insert(
&slash_era,
stash,
&era_slash,
);
era_slash
};
// compare the era slash against other eras in the same span.
{
let mut spans = fetch_spans::<T>(
stash,
window_start,
&mut reward_payout,
&mut nom_slashed,
reward_proportion,
);
let target_span = spans.compare_and_update_span_slash(
slash_era,
era_slash,
);
if target_span == Some(spans.span_index()) {
// Chill the nominator outright, ending the slashing span.
spans.end_span(now);
<Module<T>>::chill_stash(stash);
}
}
nominators_slashed.push((stash.clone(), nom_slashed));
}
reward_payout
}
// helper struct for managing a set of spans we are currently inspecting.
// writes alterations to disk on drop, but only if a slash has been carried out.
//
// NOTE: alterations to slashing metadata should not be done after this is dropped.
// dropping this struct applies any necessary slashes, which can lead to free balance
// being 0, and the account being garbage-collected -- a dead account should get no new
// metadata.
struct InspectingSpans<'a, T: Trait + 'a> {
dirty: bool,
window_start: EraIndex,
stash: &'a T::AccountId,
spans: SlashingSpans,
paid_out: &'a mut BalanceOf<T>,
slash_of: &'a mut BalanceOf<T>,
reward_proportion: Perbill,
_marker: rstd::marker::PhantomData<T>,
}
// fetches the slashing spans record for a stash account, initializing it if necessary.
fn fetch_spans<'a, T: Trait + 'a>(
stash: &'a T::AccountId,
window_start: EraIndex,
paid_out: &'a mut BalanceOf<T>,
slash_of: &'a mut BalanceOf<T>,
reward_proportion: Perbill,
) -> InspectingSpans<'a, T> {
let spans = <Module<T> as Store>::SlashingSpans::get(stash).unwrap_or_else(|| {
let spans = SlashingSpans::new(window_start);
<Module<T> as Store>::SlashingSpans::insert(stash, &spans);
spans
});
InspectingSpans {
dirty: false,
window_start,
stash,
spans,
slash_of,
paid_out,
reward_proportion,
_marker: rstd::marker::PhantomData,
}
}
impl<'a, T: 'a + Trait> InspectingSpans<'a, T> {
fn span_index(&self) -> SpanIndex {
self.spans.span_index
}
fn end_span(&mut self, now: EraIndex) {
self.dirty = self.spans.end_span(now) || self.dirty;
}
fn add_slash(&mut self, amount: BalanceOf<T>) {
*self.slash_of += amount;
}
// find the span index of the given era, if covered.
fn era_span(&self, era: EraIndex) -> Option<SlashingSpan> {
self.spans.iter().find(|span| span.contains_era(era))
}
// compares the slash in an era to the overall current span slash.
// if it's higher, applies the difference of the slashes and then updates the span on disk.
//
// returns the span index of the era where the slash occurred, if any.
fn compare_and_update_span_slash(
&mut self,
slash_era: EraIndex,
slash: BalanceOf<T>,
) -> Option<SpanIndex> {
let target_span = self.era_span(slash_era)?;
let span_slash_key = (self.stash.clone(), target_span.index);
let mut span_record = <Module<T> as Store>::SpanSlash::get(&span_slash_key);
let mut changed = false;
let reward = if span_record.slashed < slash {
// new maximum span slash. apply the difference.
let difference = slash - span_record.slashed;
span_record.slashed = slash;
// compute reward.
let reward = REWARD_F1
* (self.reward_proportion * slash).saturating_sub(span_record.paid_out);
self.add_slash(difference);
changed = true;
reward
} else if span_record.slashed == slash {
// compute reward. no slash difference to apply.
REWARD_F1 * (self.reward_proportion * slash).saturating_sub(span_record.paid_out)
} else {
Zero::zero()
};
if !reward.is_zero() {
changed = true;
span_record.paid_out += reward;
*self.paid_out += reward;
}
if changed {
self.dirty = true;
<Module<T> as Store>::SpanSlash::insert(&span_slash_key, &span_record);
}
Some(target_span.index)
}
}
impl<'a, T: 'a + Trait> Drop for InspectingSpans<'a, T> {
fn drop(&mut self) {
// only update on disk if we slashed this account.
if !self.dirty { return }
if let Some((start, end)) = self.spans.prune(self.window_start) {
for span_index in start..end {
<Module<T> as Store>::SpanSlash::remove(&(self.stash.clone(), span_index));
}
}
<Module<T> as Store>::SlashingSpans::insert(self.stash, &self.spans);
}
}
/// Clear slashing metadata for an obsolete era.
pub(crate) fn clear_era_metadata<T: Trait>(obsolete_era: EraIndex) {
<Module<T> as Store>::ValidatorSlashInEra::remove_prefix(&obsolete_era);
<Module<T> as Store>::NominatorSlashInEra::remove_prefix(&obsolete_era);
}
/// Clear slashing metadata for a dead account.
pub(crate) fn clear_stash_metadata<T: Trait>(stash: &T::AccountId) {
let spans = match <Module<T> as Store>::SlashingSpans::take(stash) {
None => return,
Some(s) => s,
};
// kill slashing-span metadata for account.
//
// this can only happen while the account is staked _if_ they are completely slashed.
// in that case, they may re-bond, but it would count again as span 0. Further ancient
// slashes would slash into this new bond, since metadata has now been cleared.
for span in spans.iter() {
<Module<T> as Store>::SpanSlash::remove(&(stash.clone(), span.index));
}
}
// apply the slash to a stash account, deducting any missing funds from the reward
// payout, saturating at 0. this is mildly unfair but also an edge-case that
// can only occur when overlapping locked funds have been slashed.
fn do_slash<T: Trait>(
stash: &T::AccountId,
value: BalanceOf<T>,
reward_payout: &mut BalanceOf<T>,
slashed_imbalance: &mut NegativeImbalanceOf<T>,
) {
let controller = match <Module<T>>::bonded(stash) {
None => return, // defensive: should always exist.
Some(c) => c,
};
let mut ledger = match <Module<T>>::ledger(&controller) {
Some(ledger) => ledger,
None => return, // nothing to do.
};
let value = ledger.slash(value, T::Currency::minimum_balance());
if !value.is_zero() {
let (imbalance, missing) = T::Currency::slash(stash, value);
slashed_imbalance.subsume(imbalance);
if !missing.is_zero() {
// deduct overslash from the reward payout
*reward_payout = reward_payout.saturating_sub(missing);
}
<Module<T>>::update_ledger(&controller, &ledger);
// trigger the event
<Module<T>>::deposit_event(
super::RawEvent::Slash(stash.clone(), value)
);
}
}
/// Apply a previously-unapplied slash.
pub(crate) fn apply_slash<T: Trait>(unapplied_slash: UnappliedSlash<T::AccountId, BalanceOf<T>>) {
let mut slashed_imbalance = NegativeImbalanceOf::<T>::zero();
let mut reward_payout = unapplied_slash.payout;
do_slash::<T>(
&unapplied_slash.validator,
unapplied_slash.own,
&mut reward_payout,
&mut slashed_imbalance,
);
for &(ref nominator, nominator_slash) in &unapplied_slash.others {
do_slash::<T>(
&nominator,
nominator_slash,
&mut reward_payout,
&mut slashed_imbalance,
);
}
pay_reporters::<T>(reward_payout, slashed_imbalance, &unapplied_slash.reporters);
}
/// Apply a reward payout to some reporters, paying the rewards out of the slashed imbalance.
fn pay_reporters<T: Trait>(
reward_payout: BalanceOf<T>,
slashed_imbalance: NegativeImbalanceOf<T>,
reporters: &[T::AccountId],
) {
if reward_payout.is_zero() || reporters.is_empty() {
// nobody to pay out to or nothing to pay;
// just treat the whole value as slashed.
T::Slash::on_unbalanced(slashed_imbalance);
return
}
// take rewards out of the slashed imbalance.
let reward_payout = reward_payout.min(slashed_imbalance.peek());
let (mut reward_payout, mut value_slashed) = slashed_imbalance.split(reward_payout);
let per_reporter = reward_payout.peek() / (reporters.len() as u32).into();
for reporter in reporters {
let (reporter_reward, rest) = reward_payout.split(per_reporter);
reward_payout = rest;
// this cancels out the reporter reward imbalance internally, leading
// to no change in total issuance.
T::Currency::resolve_creating(reporter, reporter_reward);
}
// the rest goes to the on-slash imbalance handler (e.g. treasury)
value_slashed.subsume(reward_payout); // remainder of reward division remains.
T::Slash::on_unbalanced(value_slashed);
}
// TODO: function for undoing a slash.
//
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn span_contains_era() {
// unbounded end
let span = SlashingSpan { index: 0, start: 1000, length: None };
assert!(!span.contains_era(0));
assert!(!span.contains_era(999));
assert!(span.contains_era(1000));
assert!(span.contains_era(1001));
assert!(span.contains_era(10000));
// bounded end - non-inclusive range.
let span = SlashingSpan { index: 0, start: 1000, length: Some(10) };
assert!(!span.contains_era(0));
assert!(!span.contains_era(999));
assert!(span.contains_era(1000));
assert!(span.contains_era(1001));
assert!(span.contains_era(1009));
assert!(!span.contains_era(1010));
assert!(!span.contains_era(1011));
}
#[test]
fn single_slashing_span() {
let spans = SlashingSpans {
span_index: 0,
last_start: 1000,
prior: Vec::new(),
};
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![SlashingSpan { index: 0, start: 1000, length: None }],
);
}
#[test]
fn many_prior_spans() {
let spans = SlashingSpans {
span_index: 10,
last_start: 1000,
prior: vec![10, 9, 8, 10],
};
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 10, start: 1000, length: None },
SlashingSpan { index: 9, start: 990, length: Some(10) },
SlashingSpan { index: 8, start: 981, length: Some(9) },
SlashingSpan { index: 7, start: 973, length: Some(8) },
SlashingSpan { index: 6, start: 963, length: Some(10) },
],
)
}
#[test]
fn pruning_spans() {
let mut spans = SlashingSpans {
span_index: 10,
last_start: 1000,
prior: vec![10, 9, 8, 10],
};
assert_eq!(spans.prune(981), Some((6, 8)));
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 10, start: 1000, length: None },
SlashingSpan { index: 9, start: 990, length: Some(10) },
SlashingSpan { index: 8, start: 981, length: Some(9) },
],
);
assert_eq!(spans.prune(982), None);
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 10, start: 1000, length: None },
SlashingSpan { index: 9, start: 990, length: Some(10) },
SlashingSpan { index: 8, start: 981, length: Some(9) },
],
);
assert_eq!(spans.prune(989), None);
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 10, start: 1000, length: None },
SlashingSpan { index: 9, start: 990, length: Some(10) },
SlashingSpan { index: 8, start: 981, length: Some(9) },
],
);
assert_eq!(spans.prune(1000), Some((8, 10)));
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 10, start: 1000, length: None },
],
);
assert_eq!(spans.prune(2000), None);
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 10, start: 2000, length: None },
],
);
// now all in one shot.
let mut spans = SlashingSpans {
span_index: 10,
last_start: 1000,
prior: vec![10, 9, 8, 10],
};
assert_eq!(spans.prune(2000), Some((6, 10)));
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 10, start: 2000, length: None },
],
);
}
#[test]
fn ending_span() {
let mut spans = SlashingSpans {
span_index: 1,
last_start: 10,
prior: Vec::new(),
};
assert!(spans.end_span(10));
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 2, start: 11, length: None },
SlashingSpan { index: 1, start: 10, length: Some(1) },
],
);
assert!(spans.end_span(15));
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 3, start: 16, length: None },
SlashingSpan { index: 2, start: 11, length: Some(5) },
SlashingSpan { index: 1, start: 10, length: Some(1) },
],
);
// does nothing if not a valid end.
assert!(!spans.end_span(15));
assert_eq!(
spans.iter().collect::<Vec<_>>(),
vec![
SlashingSpan { index: 3, start: 16, length: None },
SlashingSpan { index: 2, start: 11, length: Some(5) },
SlashingSpan { index: 1, start: 10, length: Some(1) },
],
);
}
}