past-session validator discovery APIs (#2009)

* guide: fix formatting for SessionInfo module

* primitives: SessionInfo type

* punt on approval keys

* ah, revert the type alias

* session info runtime module skeleton

* update the guide

* runtime/configuration: sync with the guide

* runtime/configuration: setters for newly added fields

* runtime/configuration: set codec indexes

* runtime/configuration: update test

* primitives: fix SessionInfo definition

* runtime/session_info: initial impl

* runtime/session_info: use initializer for session handling (wip)

* runtime/session_info: mock authority discovery trait

* guide: update the initializer's order

* runtime/session_info: tests skeleton

* runtime/session_info: store n_delay_tranches in Configuration

* runtime/session_info: punt on approval keys

* runtime/session_info: add some basic tests

* Update primitives/src/v1.rs

* small fixes

* remove codec index annotation on structs

* fix off-by-one error

* validator_discovery: accept a session index

* runtime: replace validator_discovery api with session_info

* Update runtime/parachains/src/session_info.rs

Co-authored-by: Sergei Shulepov <sergei@parity.io>

* runtime/session_info: add a comment about missing entries

* runtime/session_info: define the keys

* util: expose connect_to_past_session_validators

* util: allow session_info requests for jobs

* runtime-api: add mock test for session_info

* collator-protocol: add session_index to test state

* util: fix error message for runtime error

* fix compilation

* fix tests after merge with master

Co-authored-by: Sergei Shulepov <sergei@parity.io>

polkadot/roadmap/implementers-guide/src/runtime/initializer.md

@@ -23,7 +23,7 @@ The other parachains modules are initialized in this order:
 1. Paras
 1. Scheduler
 1. Inclusion
-1. Validity
+1. SessionInfo
 1. DMP
 1. UMP
 1. HRMP

polkadot/roadmap/implementers-guide/src/runtime/session_info.md

@@ -30,11 +30,11 @@ struct SessionInfo {
     // no-show.
     no_show_slots: u32,
     /// The number of validators needed to approve a block.
-	needed_approvals: u32,
+    needed_approvals: u32,
 }
 ```
 
-Storage Layout: 
+Storage Layout:
 
 ```rust
 /// The earliest session for which previous session info is stored.
@@ -45,11 +45,10 @@ Sessions: map SessionIndex => Option<SessionInfo>,
 
 ## Session Change
 
-1. Update the `CurrentSessionIndex`.
 1. Update `EarliestStoredSession` based on `config.dispute_period` and remove all entries from `Sessions` from the previous value up to the new value.
 1. Create a new entry in `Sessions` with information about the current session.
 
 ## Routines
 
 * `earliest_stored_session() -> SessionIndex`: Yields the earliest session for which we have information stored.
-* `session_info(session: SessionIndex) -> Option<SessionInfo>`: Yields the session info for the given session, if stored.
+* `session_info(session: SessionIndex) -> Option<SessionInfo>`: Yields the session info for the given session, if stored.

polkadot/roadmap/implementers-guide/src/types/overseer-protocol.md

@@ -424,14 +424,8 @@ enum RuntimeApiRequest {
 	Validators(ResponseChannel<Vec<ValidatorId>>),
 	/// Get the validator groups and rotation info.
 	ValidatorGroups(ResponseChannel<(Vec<Vec<ValidatorIndex>>, GroupRotationInfo)>),
-	/// Get the session index for children of the block. This can be used to construct a signing
-	/// context.
-	SessionIndex(ResponseChannel<SessionIndex>),
-	/// Get the validation code for a specific para, using the given occupied core assumption.
-	ValidationCode(ParaId, OccupiedCoreAssumption, ResponseChannel<Option<ValidationCode>>),
-	/// Fetch the historical validation code used by a para for candidates executed in
-	/// the context of a given block height in the current chain.
-	HistoricalValidationCode(ParaId, BlockNumber, ResponseChannel<Option<ValidationCode>>),
+	/// Get information about all availability cores.
+	AvailabilityCores(ResponseChannel<Vec<CoreState>>),
 	/// with the given occupied core assumption.
 	PersistedValidationData(
 		ParaId,
@@ -450,12 +444,25 @@ enum RuntimeApiRequest {
 		CandidateCommitments,
 		RuntimeApiSender<bool>,
 	),
-	/// Get information about all availability cores.
-	AvailabilityCores(ResponseChannel<Vec<CoreState>>),
+	/// Get the session index for children of the block. This can be used to construct a signing
+	/// context.
+	SessionIndexForChild(ResponseChannel<SessionIndex>),
+	/// Get the validation code for a specific para, using the given occupied core assumption.
+	ValidationCode(ParaId, OccupiedCoreAssumption, ResponseChannel<Option<ValidationCode>>),
+	/// Fetch the historical validation code used by a para for candidates executed in
+	/// the context of a given block height in the current chain.
+	HistoricalValidationCode(ParaId, BlockNumber, ResponseChannel<Option<ValidationCode>>),
 	/// Get a committed candidate receipt for all candidates pending availability.
 	CandidatePendingAvailability(ParaId, ResponseChannel<Option<CommittedCandidateReceipt>>),
 	/// Get all events concerning candidates in the last block.
 	CandidateEvents(ResponseChannel<Vec<CandidateEvent>>),
+	/// Get the session info for the given session, if stored.
+	SessionInfo(SessionIndex, ResponseChannel<Option<SessionInfo>>),
+	/// Get all the pending inbound messages in the downward message queue for a para.
+	DmqContents(ParaId, ResponseChannel<Vec<InboundDownwardMessage<BlockNumber>>>),
+	/// Get the contents of all channels addressed to the given recipient. Channels that have no
+	/// messages in them are also included.
+	InboundHrmpChannelsContents(ParaId, ResponseChannel<BTreeMap<ParaId, Vec<InboundHrmpMessage<BlockNumber>>>>),
 }
 
 enum RuntimeApiMessage {

polkadot/roadmap/implementers-guide/src/types/runtime.md

@@ -12,6 +12,9 @@ struct HostConfiguration {
 	pub validation_upgrade_frequency: BlockNumber,
 	/// The delay, in blocks, before a validation upgrade is applied.
 	pub validation_upgrade_delay: BlockNumber,
+	/// The acceptance period, in blocks. This is the amount of blocks after availability that validators
+	/// and fishermen have to perform secondary checks or issue reports.
+	pub acceptance_period: BlockNumber,
 	/// The maximum validation code size, in bytes.
 	pub max_code_size: u32,
 	/// The maximum head-data size, in bytes.
@@ -37,6 +40,8 @@ struct HostConfiguration {
 	/// submitting an approval vote before a validator is considered a no-show.
 	/// Must be at least 1.
 	pub no_show_slots: u32,
+	/// The number of delay tranches in total.
+	pub n_delay_tranches: u32,
 	/// The width of the zeroth delay tranche for approval assignments. This many delay tranches
 	/// beyond 0 are all consolidated to form a wide 0 tranche.
 	pub zeroth_delay_tranche_width: u32,