Offchain Phragmén BREAKING. (#4517)

* Initial skeleton for offchain phragmen

* Basic compact encoding decoding for results

* add compact files

* Bring back Self::ensure_storage_upgraded();

* Make staking use compact stuff.

* First seemingly working version of reduce, full of todos

* Everything phragmen related works again.

* Signing made easier, still issues.

* Signing from offchain compile fine 😎

* make compact work with staked asssignment

* Evaluation basics are in place.

* Move reduce into crate. Document stuff

* move reduce into no_std

* Add files

* Remove other std deps. Runtime compiles

* Seemingly it is al stable; cycle implemented but not integrated.

* Add fuzzing code.

* Cleanup reduce a bit more.

* a metric ton of tests for staking; wip 🔨

* Implement a lot more of the tests.

* wip getting the unsigned stuff to work

* A bit gleanup for unsigned debug

* Clean and finalize compact code.

* Document reduce.

* Still problems with signing

* We officaly duct taped the transaction submission stuff. 🤓

* Deadlock with keys again

* Runtime builds

* Unsigned test works 🙌

* Some cleanups

* Make all the tests compile and stuff

* Minor cleanup

* fix more merge stuff

* Most tests work again.

* a very nasty bug in reduce

* Fix all integrations

* Fix more todos

* Revamp everything and everything

* Remove bogus test

* Some review grumbles.

* Some fixes

* Fix doc test

* loop for submission

* Fix cli, keyring etc.

* some cleanup

* Fix staking tests again

* fix per-things; bring patches from benchmarking

* better score prediction

* Add fuzzer, more patches.

* Some fixes

* More docs

* Remove unused generics

* Remove max-nominator footgun

* Better fuzzer

* Disable it ❌

* Bump.

* Another round of self-review

* Refactor a lot

* More major fixes in perThing

* Add new fuzz file

* Update lock

* fix fuzzing code.

* Fix nominator retain test

* Add slashing check

* Update frame/staking/src/tests.rs

Co-Authored-By: Joshy Orndorff <JoshOrndorff@users.noreply.github.com>

* Some formatting nits

* Review comments.

* Fix cargo file

* Almost all tests work again

* Update frame/staking/src/tests.rs

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

* Fix review comments

* More review stuff

* Some nits

* Fix new staking / session / babe relation

* Update primitives/phragmen/src/lib.rs

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

* Update primitives/phragmen/src/lib.rs

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

* Update primitives/phragmen/compact/src/lib.rs

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

* Some doc updates to slashing

* Fix derive

* Remove imports

* Remove unimplemented tests

* nits

* Remove dbg

* Better fuzzing params

* Remove unused pref map

* Deferred Slashing/Offence for offchain Phragmen  (#5151)

* Some boilerplate

* Add test

* One more test

* Review comments

* Fix build

* review comments

* fix more

* fix build

* Some cleanups and self-reviews

* More minor self reviews

* Final nits

* Some merge fixes.

* opt comment

* Fix build

* Fix build again.

* Update frame/staking/fuzz/fuzz_targets/submit_solution.rs

Co-Authored-By: Gavin Wood <gavin@parity.io>

* Update frame/staking/src/slashing.rs

Co-Authored-By: Gavin Wood <gavin@parity.io>

* Update frame/staking/src/offchain_election.rs

Co-Authored-By: Gavin Wood <gavin@parity.io>

* Fix review comments

* fix test

* === 🔑 Revamp without staking key.

* final round of changes.

* Fix cargo-deny

* Update frame/staking/src/lib.rs

Co-Authored-By: Gavin Wood <gavin@parity.io>

Co-authored-by: Joshy Orndorff <JoshOrndorff@users.noreply.github.com>
Co-authored-by: thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Gavin Wood <gavin@parity.io>

substrate/frame/session/src/lib.rs

@@ -102,13 +102,15 @@
 use sp_std::{prelude::*, marker::PhantomData, ops::{Sub, Rem}};
 use codec::Decode;
 use sp_runtime::{KeyTypeId, Perbill, RuntimeAppPublic, BoundToRuntimeAppPublic};
-use sp_runtime::traits::{Convert, Zero, Member, OpaqueKeys};
+use sp_runtime::traits::{Convert, Zero, Member, OpaqueKeys, Saturating};
 use sp_staking::SessionIndex;
 use frame_support::{
 	ensure, decl_module, decl_event, decl_storage, decl_error, ConsensusEngineId, Parameter,
-	weights::{Weight, SimpleDispatchInfo, WeighData},
-	traits::{Get, FindAuthor, ValidatorRegistration},
+	traits::{
+		Get, FindAuthor, ValidatorRegistration, EstimateNextSessionRotation, EstimateNextNewSession,
+	},
 	dispatch::{self, DispatchResult, DispatchError},
+	weights::{Weight, SimpleDispatchInfo, WeighData},
 };
 use frame_system::{self as system, ensure_signed};
 
@@ -147,6 +149,29 @@ impl<
 	}
 }
 
+impl<
+	BlockNumber: Rem<Output=BlockNumber> + Sub<Output=BlockNumber> + Zero + PartialOrd + Saturating + Clone,
+	Period: Get<BlockNumber>,
+	Offset: Get<BlockNumber>,
+> EstimateNextSessionRotation<BlockNumber> for PeriodicSessions<Period, Offset> {
+	fn estimate_next_session_rotation(now: BlockNumber) -> Option<BlockNumber> {
+		let offset = Offset::get();
+		let period = Period::get();
+		Some(if now > offset {
+			let block_after_last_session = (now.clone() - offset) % period.clone();
+			if block_after_last_session > Zero::zero() {
+				now.saturating_add(
+					period.saturating_sub(block_after_last_session)
+				)
+			} else {
+				Zero::zero()
+			}
+		} else {
+			offset
+		})
+	}
+}
+
 /// A trait for managing creation of new validator set.
 pub trait SessionManager<ValidatorId> {
 	/// Plan a new session, and optionally provide the new validator set.
@@ -330,6 +355,11 @@ pub trait Trait: frame_system::Trait {
 	/// Indicator for when to end the session.
 	type ShouldEndSession: ShouldEndSession<Self::BlockNumber>;
 
+	/// Something that can predict the next session rotation. This should typically come from the
+	/// same logical unit that provides [`ShouldEndSession`], yet, it gives a best effort estimate.
+	/// It is helpful to implement [`EstimateNextNewSession`].
+	type NextSessionRotation: EstimateNextSessionRotation<Self::BlockNumber>;
+
 	/// Handler for managing new session.
 	type SessionManager: SessionManager<Self::ValidatorId>;
 
@@ -735,3 +765,11 @@ impl<T: Trait, Inner: FindAuthor<u32>> FindAuthor<T::ValidatorId>
 		validators.get(i as usize).map(|k| k.clone())
 	}
 }
+
+impl<T: Trait> EstimateNextNewSession<T::BlockNumber> for Module<T> {
+	/// This session module always calls new_session and next_session at the same time, hence we
+	/// do a simple proxy and pass the function to next rotation.
+	fn estimate_next_new_session(now: T::BlockNumber) -> Option<T::BlockNumber> {
+		T::NextSessionRotation::estimate_next_session_rotation(now)
+	}
+}