Reorganising the repository - external renames and moves (#4074)

* Adding first rough ouline of the repository structure * Remove old CI stuff * add title * formatting fixes * move node-exits job's script to scripts dir * Move docs into subdir * move to bin * move maintainence scripts, configs and helpers into its own dir * add .local to ignore * move core->client * start up 'test' area * move test client * move test runtime * make test move compile * Add dependencies rule enforcement. * Fix indexing. * Update docs to reflect latest changes * Moving /srml->/paint * update docs * move client/sr-* -> primitives/ * clean old readme * remove old broken code in rhd * update lock * Step 1. * starting to untangle client * Fix after merge. * start splitting out client interfaces * move children and blockchain interfaces * Move trie and state-machine to primitives. * Fix WASM builds. * fixing broken imports * more interface moves * move backend and light to interfaces * move CallExecutor * move cli off client * moving around more interfaces * re-add consensus crates into the mix * fix subkey path * relieve client from executor * starting to pull out client from grandpa * move is_decendent_of out of client * grandpa still depends on client directly * lemme tests pass * rename srml->paint * Make it compile. * rename interfaces->client-api * Move keyring to primitives. * fixup libp2p dep * fix broken use * allow dependency enforcement to fail * move fork-tree * Moving wasm-builder * make env * move build-script-utils * fixup broken crate depdencies and names * fix imports for authority discovery * fix typo * update cargo.lock * fixing imports * Fix paths and add missing crates * re-add missing crates
2026-05-30 17:31:03 +00:00 · 2019-11-14 21:51:17 +01:00
parent becc3b0a4f
commit 60e5011c72
809 changed files with 7801 additions and 6464 deletions
@@ -0,0 +1,787 @@
+// Copyright 2018-2019 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/>.
+
+//! Utilities for dealing with authorities, authority sets, and handoffs.
+
+use fork_tree::ForkTree;
+use parking_lot::RwLock;
+use grandpa::voter_set::VoterSet;
+use codec::{Encode, Decode};
+use log::{debug, info};
+use substrate_telemetry::{telemetry, CONSENSUS_INFO};
+use fg_primitives::{AuthorityId, AuthorityList};
+
+use std::cmp::Ord;
+use std::fmt::Debug;
+use std::ops::Add;
+use std::sync::Arc;
+
+/// A shared authority set.
+pub(crate) struct SharedAuthoritySet<H, N> {
+	inner: Arc<RwLock<AuthoritySet<H, N>>>,
+}
+
+impl<H, N> Clone for SharedAuthoritySet<H, N> {
+	fn clone(&self) -> Self {
+		SharedAuthoritySet { inner: self.inner.clone() }
+	}
+}
+
+impl<H, N> SharedAuthoritySet<H, N> {
+	/// Acquire a reference to the inner read-write lock.
+	pub(crate) fn inner(&self) -> &RwLock<AuthoritySet<H, N>> {
+		&*self.inner
+	}
+}
+
+impl<H: Eq, N> SharedAuthoritySet<H, N>
+where N: Add<Output=N> + Ord + Clone + Debug,
+	  H: Clone + Debug
+{
+	/// Get the earliest limit-block number, if any.
+	pub(crate) fn current_limit(&self) -> Option<N> {
+		self.inner.read().current_limit()
+	}
+
+	/// Get the current set ID. This is incremented every time the set changes.
+	pub(crate) fn set_id(&self) -> u64 {
+		self.inner.read().set_id
+	}
+
+	/// Get the current authorities and their weights (for the current set ID).
+	pub(crate) fn current_authorities(&self) -> VoterSet<AuthorityId> {
+		self.inner.read().current_authorities.iter().cloned().collect()
+	}
+}
+
+impl<H, N> From<AuthoritySet<H, N>> for SharedAuthoritySet<H, N> {
+	fn from(set: AuthoritySet<H, N>) -> Self {
+		SharedAuthoritySet { inner: Arc::new(RwLock::new(set)) }
+	}
+}
+
+/// Status of the set after changes were applied.
+#[derive(Debug)]
+pub(crate) struct Status<H, N> {
+	/// Whether internal changes were made.
+	pub(crate) changed: bool,
+	/// `Some` when underlying authority set has changed, containing the
+	/// block where that set changed.
+	pub(crate) new_set_block: Option<(H, N)>,
+}
+
+/// A set of authorities.
+#[derive(Debug, Clone, Encode, Decode, PartialEq)]
+pub(crate) struct AuthoritySet<H, N> {
+	pub(crate) current_authorities: AuthorityList,
+	pub(crate) set_id: u64,
+	// Tree of pending standard changes across forks. Standard changes are
+	// enacted on finality and must be enacted (i.e. finalized) in-order across
+	// a given branch
+	pub(crate) pending_standard_changes: ForkTree<H, N, PendingChange<H, N>>,
+	// Pending forced changes across different forks (at most one per fork).
+	// Forced changes are enacted on block depth (not finality), for this reason
+	// only one forced change should exist per fork.
+	pub(crate) pending_forced_changes: Vec<PendingChange<H, N>>,
+}
+
+impl<H, N> AuthoritySet<H, N>
+where H: PartialEq,
+	  N: Ord,
+{
+	/// Get a genesis set with given authorities.
+	pub(crate) fn genesis(initial: AuthorityList) -> Self {
+		AuthoritySet {
+			current_authorities: initial,
+			set_id: 0,
+			pending_standard_changes: ForkTree::new(),
+			pending_forced_changes: Vec::new(),
+		}
+	}
+
+	/// Get the current set id and a reference to the current authority set.
+	pub(crate) fn current(&self) -> (u64, &[(AuthorityId, u64)]) {
+		(self.set_id, &self.current_authorities[..])
+	}
+}
+
+impl<H: Eq, N> AuthoritySet<H, N>
+where
+	N: Add<Output=N> + Ord + Clone + Debug,
+	H: Clone + Debug
+{
+	fn add_standard_change<F, E>(
+		&mut self,
+		pending: PendingChange<H, N>,
+		is_descendent_of: &F,
+	) -> Result<(), fork_tree::Error<E>> where
+		F: Fn(&H, &H) -> Result<bool, E>,
+		E:  std::error::Error,
+	{
+		let hash = pending.canon_hash.clone();
+		let number = pending.canon_height.clone();
+
+		debug!(target: "afg", "Inserting potential standard set change signaled at block {:?} \
+							   (delayed by {:?} blocks).",
+			   (&number, &hash), pending.delay);
+
+		self.pending_standard_changes.import(
+			hash.clone(),
+			number.clone(),
+			pending,
+			is_descendent_of,
+		)?;
+
+		debug!(target: "afg", "There are now {} alternatives for the next pending standard change (roots), \
+							   and a total of {} pending standard changes (across all forks).",
+			self.pending_standard_changes.roots().count(),
+			self.pending_standard_changes.iter().count(),
+		);
+
+		Ok(())
+	}
+
+	fn add_forced_change<F, E>(
+		&mut self,
+		pending: PendingChange<H, N>,
+		is_descendent_of: &F,
+	) -> Result<(), fork_tree::Error<E>> where
+		F: Fn(&H, &H) -> Result<bool, E>,
+		E:  std::error::Error,
+	{
+		for change in self.pending_forced_changes.iter() {
+			if change.canon_hash == pending.canon_hash ||
+				is_descendent_of(&change.canon_hash, &pending.canon_hash)?
+			{
+				return Err(fork_tree::Error::UnfinalizedAncestor);
+			}
+		}
+
+		// ordered first by effective number and then by signal-block number.
+		let key = (pending.effective_number(), pending.canon_height.clone());
+		let idx = self.pending_forced_changes
+			.binary_search_by_key(&key, |change| (
+				change.effective_number(),
+				change.canon_height.clone(),
+			))
+			.unwrap_or_else(|i| i);
+
+		debug!(target: "afg", "Inserting potential forced set change at block {:?} \
+							   (delayed by {:?} blocks).",
+			   (&pending.canon_height, &pending.canon_hash), pending.delay);
+
+		self.pending_forced_changes.insert(idx, pending);
+
+		debug!(target: "afg", "There are now {} pending forced changes.", self.pending_forced_changes.len());
+
+		Ok(())
+	}
+
+	/// Note an upcoming pending transition. Multiple pending standard changes
+	/// on the same branch can be added as long as they don't overlap. Forced
+	/// changes are restricted to one per fork. This method assumes that changes
+	/// on the same branch will be added in-order. The given function
+	/// `is_descendent_of` should return `true` if the second hash (target) is a
+	/// descendent of the first hash (base).
+	pub(crate) fn add_pending_change<F, E>(
+		&mut self,
+		pending: PendingChange<H, N>,
+		is_descendent_of: &F,
+	) -> Result<(), fork_tree::Error<E>> where
+		F: Fn(&H, &H) -> Result<bool, E>,
+		E:  std::error::Error,
+	{
+		match pending.delay_kind {
+			DelayKind::Best { .. } => {
+				self.add_forced_change(pending, is_descendent_of)
+			},
+			DelayKind::Finalized => {
+				self.add_standard_change(pending, is_descendent_of)
+			},
+		}
+	}
+
+	/// Inspect pending changes. Standard pending changes are iterated first,
+	/// and the changes in the tree are traversed in pre-order, afterwards all
+	/// forced changes are iterated.
+	pub(crate) fn pending_changes(&self) -> impl Iterator<Item=&PendingChange<H, N>> {
+		self.pending_standard_changes.iter().map(|(_, _, c)| c)
+			.chain(self.pending_forced_changes.iter())
+	}
+
+	/// Get the earliest limit-block number, if any. If there are pending changes across
+	/// different forks, this method will return the earliest effective number (across the
+	/// different branches). Only standard changes are taken into account for the current
+	/// limit, since any existing forced change should preclude the voter from voting.
+	pub(crate) fn current_limit(&self) -> Option<N> {
+		self.pending_standard_changes.roots()
+			.min_by_key(|&(_, _, c)| c.effective_number())
+			.map(|(_, _, c)| c.effective_number())
+	}
+
+	/// Apply or prune any pending transitions based on a best-block trigger.
+	///
+	/// Returns `Ok((median, new_set))` when a forced change has occurred. The
+	/// median represents the median last finalized block at the time the change
+	/// was signaled, and it should be used as the canon block when starting the
+	/// new grandpa voter. Only alters the internal state in this case.
+	///
+	/// These transitions are always forced and do not lead to justifications
+	/// which light clients can follow.
+	pub(crate) fn apply_forced_changes<F, E>(
+		&self,
+		best_hash: H,
+		best_number: N,
+		is_descendent_of: &F,
+	) -> Result<Option<(N, Self)>, E>
+		where F: Fn(&H, &H) -> Result<bool, E>,
+	{
+		let mut new_set = None;
+
+		for change in self.pending_forced_changes.iter()
+			.take_while(|c| c.effective_number() <= best_number) // to prevent iterating too far
+			.filter(|c| c.effective_number() == best_number)
+		{
+			// check if the given best block is in the same branch as the block that signaled the change.
+			if is_descendent_of(&change.canon_hash, &best_hash)? {
+				// apply this change: make the set canonical
+				info!(target: "finality", "Applying authority set change forced at block #{:?}",
+					  change.canon_height);
+				telemetry!(CONSENSUS_INFO; "afg.applying_forced_authority_set_change";
+					"block" => ?change.canon_height
+				);
+
+				let median_last_finalized = match change.delay_kind {
+					DelayKind::Best { ref median_last_finalized } => median_last_finalized.clone(),
+					_ => unreachable!("pending_forced_changes only contains forced changes; forced changes have delay kind Best; qed."),
+				};
+
+				new_set = Some((median_last_finalized, AuthoritySet {
+					current_authorities: change.next_authorities.clone(),
+					set_id: self.set_id + 1,
+					pending_standard_changes: ForkTree::new(), // new set, new changes.
+					pending_forced_changes: Vec::new(),
+				}));
+
+				break;
+			}
+
+			// we don't wipe forced changes until another change is
+			// applied
+		}
+
+		Ok(new_set)
+	}
+
+	/// Apply or prune any pending transitions based on a finality trigger. This
+	/// method ensures that if there are multiple changes in the same branch,
+	/// finalizing this block won't finalize past multiple transitions (i.e.
+	/// transitions must be finalized in-order). The given function
+	/// `is_descendent_of` should return `true` if the second hash (target) is a
+	/// descendent of the first hash (base).
+	///
+	/// When the set has changed, the return value will be `Ok(Some((H, N)))`
+	/// which is the canonical block where the set last changed (i.e. the given
+	/// hash and number).
+	pub(crate) fn apply_standard_changes<F, E>(
+		&mut self,
+		finalized_hash: H,
+		finalized_number: N,
+		is_descendent_of: &F,
+	) -> Result<Status<H, N>, fork_tree::Error<E>>
+		where F: Fn(&H, &H) -> Result<bool, E>,
+			  E: std::error::Error,
+	{
+		let mut status = Status {
+			changed: false,
+			new_set_block: None,
+		};
+
+		match self.pending_standard_changes.finalize_with_descendent_if(
+			&finalized_hash,
+			finalized_number.clone(),
+			is_descendent_of,
+			|change| change.effective_number() <= finalized_number
+		)? {
+			fork_tree::FinalizationResult::Changed(change) => {
+				status.changed = true;
+
+				// if we are able to finalize any standard change then we can
+				// discard all pending forced changes (on different forks)
+				self.pending_forced_changes.clear();
+
+				if let Some(change) = change {
+					info!(target: "finality", "Applying authority set change scheduled at block #{:?}",
+						  change.canon_height);
+					telemetry!(CONSENSUS_INFO; "afg.applying_scheduled_authority_set_change";
+						"block" => ?change.canon_height
+					);
+
+					self.current_authorities = change.next_authorities;
+					self.set_id += 1;
+
+					status.new_set_block = Some((
+						finalized_hash,
+						finalized_number,
+					));
+				}
+			},
+			fork_tree::FinalizationResult::Unchanged => {},
+		}
+
+		Ok(status)
+	}
+
+	/// Check whether the given finalized block number enacts any standard
+	/// authority set change (without triggering it), ensuring that if there are
+	/// multiple changes in the same branch, finalizing this block won't
+	/// finalize past multiple transitions (i.e. transitions must be finalized
+	/// in-order). Returns `Some(true)` if the block being finalized enacts a
+	/// change that can be immediately applied, `Some(false)` if the block being
+	/// finalized enacts a change but it cannot be applied yet since there are
+	/// other dependent changes, and `None` if no change is enacted. The given
+	/// function `is_descendent_of` should return `true` if the second hash
+	/// (target) is a descendent of the first hash (base).
+	pub fn enacts_standard_change<F, E>(
+		&self,
+		finalized_hash: H,
+		finalized_number: N,
+		is_descendent_of: &F,
+	) -> Result<Option<bool>, fork_tree::Error<E>>
+	where F: Fn(&H, &H) -> Result<bool, E>,
+		  E: std::error::Error,
+	{
+		self.pending_standard_changes.finalizes_any_with_descendent_if(
+			&finalized_hash,
+			finalized_number.clone(),
+			is_descendent_of,
+			|change| change.effective_number() == finalized_number
+		)
+	}
+}
+
+/// Kinds of delays for pending changes.
+#[derive(Debug, Clone, Encode, Decode, PartialEq)]
+pub(crate) enum DelayKind<N> {
+	/// Depth in finalized chain.
+	Finalized,
+	/// Depth in best chain. The median last finalized block is calculated at the time the
+	/// change was signaled.
+	Best { median_last_finalized: N },
+}
+
+/// A pending change to the authority set.
+///
+/// This will be applied when the announcing block is at some depth within
+/// the finalized or unfinalized chain.
+#[derive(Debug, Clone, Encode, PartialEq)]
+pub(crate) struct PendingChange<H, N> {
+	/// The new authorities and weights to apply.
+	pub(crate) next_authorities: AuthorityList,
+	/// How deep in the chain the announcing block must be
+	/// before the change is applied.
+	pub(crate) delay: N,
+	/// The announcing block's height.
+	pub(crate) canon_height: N,
+	/// The announcing block's hash.
+	pub(crate) canon_hash: H,
+	/// The delay kind.
+	pub(crate) delay_kind: DelayKind<N>,
+}
+
+impl<H: Decode, N: Decode> Decode for PendingChange<H, N> {
+	fn decode<I: codec::Input>(value: &mut I) -> Result<Self, codec::Error> {
+		let next_authorities = Decode::decode(value)?;
+		let delay = Decode::decode(value)?;
+		let canon_height = Decode::decode(value)?;
+		let canon_hash = Decode::decode(value)?;
+
+		let delay_kind = DelayKind::decode(value).unwrap_or(DelayKind::Finalized);
+
+		Ok(PendingChange {
+			next_authorities,
+			delay,
+			canon_height,
+			canon_hash,
+			delay_kind,
+		})
+	}
+}
+
+impl<H, N: Add<Output=N> + Clone> PendingChange<H, N> {
+	/// Returns the effective number this change will be applied at.
+	pub fn effective_number(&self) -> N {
+		self.canon_height.clone() + self.delay.clone()
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use primitives::crypto::Public;
+
+	fn static_is_descendent_of<A>(value: bool)
+		-> impl Fn(&A, &A) -> Result<bool, std::io::Error>
+	{
+		move |_, _| Ok(value)
+	}
+
+	fn is_descendent_of<A, F>(f: F) -> impl Fn(&A, &A) -> Result<bool, std::io::Error>
+		where F: Fn(&A, &A) -> bool
+	{
+		move |base, hash| Ok(f(base, hash))
+	}
+
+	#[test]
+	fn changes_iterated_in_pre_order() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_standard_changes: ForkTree::new(),
+			pending_forced_changes: Vec::new(),
+		};
+
+		let change_a = PendingChange {
+			next_authorities: Vec::new(),
+			delay: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		let change_b = PendingChange {
+			next_authorities: Vec::new(),
+			delay: 0,
+			canon_height: 5,
+			canon_hash: "hash_b",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		let change_c = PendingChange {
+			next_authorities: Vec::new(),
+			delay: 5,
+			canon_height: 10,
+			canon_hash: "hash_c",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		authorities.add_pending_change(change_a.clone(), &static_is_descendent_of(false)).unwrap();
+		authorities.add_pending_change(change_b.clone(), &static_is_descendent_of(false)).unwrap();
+		authorities.add_pending_change(change_c.clone(), &is_descendent_of(|base, hash| match (*base, *hash) {
+			("hash_a", "hash_c") => true,
+			("hash_b", "hash_c") => false,
+			_ => unreachable!(),
+		})).unwrap();
+
+		// forced changes are iterated last
+		let change_d = PendingChange {
+			next_authorities: Vec::new(),
+			delay: 2,
+			canon_height: 1,
+			canon_hash: "hash_d",
+			delay_kind: DelayKind::Best { median_last_finalized: 0 },
+		};
+
+		let change_e = PendingChange {
+			next_authorities: Vec::new(),
+			delay: 2,
+			canon_height: 0,
+			canon_hash: "hash_e",
+			delay_kind: DelayKind::Best { median_last_finalized: 0 },
+		};
+
+		authorities.add_pending_change(change_d.clone(), &static_is_descendent_of(false)).unwrap();
+		authorities.add_pending_change(change_e.clone(), &static_is_descendent_of(false)).unwrap();
+
+		assert_eq!(
+			authorities.pending_changes().collect::<Vec<_>>(),
+			vec![&change_b, &change_a, &change_c, &change_e, &change_d],
+		);
+	}
+
+	#[test]
+	fn apply_change() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_standard_changes: ForkTree::new(),
+			pending_forced_changes: Vec::new(),
+		};
+
+		let set_a = vec![(AuthorityId::from_slice(&[1; 32]), 5)];
+		let set_b = vec![(AuthorityId::from_slice(&[2; 32]), 5)];
+
+		// two competing changes at the same height on different forks
+		let change_a = PendingChange {
+			next_authorities: set_a.clone(),
+			delay: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		let change_b = PendingChange {
+			next_authorities: set_b.clone(),
+			delay: 10,
+			canon_height: 5,
+			canon_hash: "hash_b",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		authorities.add_pending_change(change_a.clone(), &static_is_descendent_of(true)).unwrap();
+		authorities.add_pending_change(change_b.clone(), &static_is_descendent_of(true)).unwrap();
+
+		assert_eq!(
+			authorities.pending_changes().collect::<Vec<_>>(),
+			vec![&change_b, &change_a],
+		);
+
+		// finalizing "hash_c" won't enact the change signaled at "hash_a" but it will prune out "hash_b"
+		let status = authorities.apply_standard_changes("hash_c", 11, &is_descendent_of(|base, hash| match (*base, *hash) {
+			("hash_a", "hash_c") => true,
+			("hash_b", "hash_c") => false,
+			_ => unreachable!(),
+		})).unwrap();
+
+		assert!(status.changed);
+		assert_eq!(status.new_set_block, None);
+		assert_eq!(
+			authorities.pending_changes().collect::<Vec<_>>(),
+			vec![&change_a],
+		);
+
+		// finalizing "hash_d" will enact the change signaled at "hash_a"
+		let status = authorities.apply_standard_changes("hash_d", 15, &is_descendent_of(|base, hash| match (*base, *hash) {
+			("hash_a", "hash_d") => true,
+			_ => unreachable!(),
+		})).unwrap();
+
+		assert!(status.changed);
+		assert_eq!(status.new_set_block, Some(("hash_d", 15)));
+
+		assert_eq!(authorities.current_authorities, set_a);
+		assert_eq!(authorities.set_id, 1);
+		assert_eq!(authorities.pending_changes().count(), 0);
+	}
+
+	#[test]
+	fn disallow_multiple_changes_being_finalized_at_once() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_standard_changes: ForkTree::new(),
+			pending_forced_changes: Vec::new(),
+		};
+
+		let set_a = vec![(AuthorityId::from_slice(&[1; 32]), 5)];
+		let set_c = vec![(AuthorityId::from_slice(&[2; 32]), 5)];
+
+		// two competing changes at the same height on different forks
+		let change_a = PendingChange {
+			next_authorities: set_a.clone(),
+			delay: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		let change_c = PendingChange {
+			next_authorities: set_c.clone(),
+			delay: 10,
+			canon_height: 30,
+			canon_hash: "hash_c",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		authorities.add_pending_change(change_a.clone(), &static_is_descendent_of(true)).unwrap();
+		authorities.add_pending_change(change_c.clone(), &static_is_descendent_of(true)).unwrap();
+
+		let is_descendent_of = is_descendent_of(|base, hash| match (*base, *hash) {
+			("hash_a", "hash_b") => true,
+			("hash_a", "hash_c") => true,
+			("hash_a", "hash_d") => true,
+
+			("hash_c", "hash_b") => false,
+			("hash_c", "hash_d") => true,
+
+			("hash_b", "hash_c") => true,
+			_ => unreachable!(),
+		});
+
+		// trying to finalize past `change_c` without finalizing `change_a` first
+		match authorities.apply_standard_changes("hash_d", 40, &is_descendent_of) {
+			Err(fork_tree::Error::UnfinalizedAncestor) => {},
+			_ => unreachable!(),
+		}
+
+		let status = authorities.apply_standard_changes("hash_b", 15, &is_descendent_of).unwrap();
+		assert!(status.changed);
+		assert_eq!(status.new_set_block, Some(("hash_b", 15)));
+
+		assert_eq!(authorities.current_authorities, set_a);
+		assert_eq!(authorities.set_id, 1);
+
+		// after finalizing `change_a` it should be possible to finalize `change_c`
+		let status = authorities.apply_standard_changes("hash_d", 40, &is_descendent_of).unwrap();
+		assert!(status.changed);
+		assert_eq!(status.new_set_block, Some(("hash_d", 40)));
+
+		assert_eq!(authorities.current_authorities, set_c);
+		assert_eq!(authorities.set_id, 2);
+	}
+
+	#[test]
+	fn enacts_standard_change_works() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_standard_changes: ForkTree::new(),
+			pending_forced_changes: Vec::new(),
+		};
+
+		let set_a = vec![(AuthorityId::from_slice(&[1; 32]), 5)];
+
+		let change_a = PendingChange {
+			next_authorities: set_a.clone(),
+			delay: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		let change_b = PendingChange {
+			next_authorities: set_a.clone(),
+			delay: 10,
+			canon_height: 20,
+			canon_hash: "hash_b",
+			delay_kind: DelayKind::Finalized,
+		};
+
+		authorities.add_pending_change(change_a.clone(), &static_is_descendent_of(false)).unwrap();
+		authorities.add_pending_change(change_b.clone(), &static_is_descendent_of(true)).unwrap();
+
+		let is_descendent_of = is_descendent_of(|base, hash| match (*base, *hash) {
+			("hash_a", "hash_d") => true,
+			("hash_a", "hash_e") => true,
+			("hash_b", "hash_d") => true,
+			("hash_b", "hash_e") => true,
+			("hash_a", "hash_c") => false,
+			("hash_b", "hash_c") => false,
+			_ => unreachable!(),
+		});
+
+		// "hash_c" won't finalize the existing change since it isn't a descendent
+		assert_eq!(
+			authorities.enacts_standard_change("hash_c", 15, &is_descendent_of).unwrap(),
+			None,
+		);
+
+		// "hash_d" at depth 14 won't work either
+		assert_eq!(
+			authorities.enacts_standard_change("hash_d", 14, &is_descendent_of).unwrap(),
+			None,
+		);
+
+		// but it should work at depth 15 (change height + depth)
+		assert_eq!(
+			authorities.enacts_standard_change("hash_d", 15, &is_descendent_of).unwrap(),
+			Some(true),
+		);
+
+		// finalizing "hash_e" at depth 20 will trigger change at "hash_b", but
+		// it can't be applied yet since "hash_a" must be applied first
+		assert_eq!(
+			authorities.enacts_standard_change("hash_e", 30, &is_descendent_of).unwrap(),
+			Some(false),
+		);
+	}
+
+	#[test]
+	fn forced_changes() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_standard_changes: ForkTree::new(),
+			pending_forced_changes: Vec::new(),
+		};
+
+		let set_a = vec![(AuthorityId::from_slice(&[1; 32]), 5)];
+		let set_b = vec![(AuthorityId::from_slice(&[2; 32]), 5)];
+
+		let change_a = PendingChange {
+			next_authorities: set_a.clone(),
+			delay: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+			delay_kind: DelayKind::Best { median_last_finalized: 42 },
+		};
+
+		let change_b = PendingChange {
+			next_authorities: set_b.clone(),
+			delay: 10,
+			canon_height: 5,
+			canon_hash: "hash_b",
+			delay_kind: DelayKind::Best { median_last_finalized: 0 },
+		};
+
+		authorities.add_pending_change(change_a, &static_is_descendent_of(false)).unwrap();
+		authorities.add_pending_change(change_b, &static_is_descendent_of(false)).unwrap();
+
+		// there's an effective change triggered at block 15 but not a standard one.
+		// so this should do nothing.
+		assert_eq!(
+			authorities.enacts_standard_change("hash_c", 15, &static_is_descendent_of(true)).unwrap(),
+			None,
+		);
+
+		// throw a standard change into the mix to prove that it's discarded
+		// for being on the same fork.
+		//
+		// NOTE: after https://github.com/paritytech/substrate/issues/1861
+		// this should still be rejected based on the "span" rule -- it overlaps
+		// with another change on the same fork.
+		let change_c = PendingChange {
+			next_authorities: set_b.clone(),
+			delay: 3,
+			canon_height: 8,
+			canon_hash: "hash_a8",
+			delay_kind: DelayKind::Best { median_last_finalized: 0 },
+		};
+
+		let is_descendent_of_a = is_descendent_of(|base: &&str, _| {
+			base.starts_with("hash_a")
+		});
+
+		assert!(authorities.add_pending_change(change_c, &is_descendent_of_a).is_err());
+
+		// too early.
+		assert!(authorities.apply_forced_changes("hash_a10", 10, &static_is_descendent_of(true)).unwrap().is_none());
+
+		// too late.
+		assert!(authorities.apply_forced_changes("hash_a16", 16, &static_is_descendent_of(true)).unwrap().is_none());
+
+		// on time -- chooses the right change.
+		assert_eq!(
+			authorities.apply_forced_changes("hash_a15", 15, &is_descendent_of_a).unwrap().unwrap(),
+			(42, AuthoritySet {
+				current_authorities: set_a,
+				set_id: 1,
+				pending_standard_changes: ForkTree::new(),
+				pending_forced_changes: Vec::new(),
+			})
+		);
+	}
+}