grandpa: report equivocations (#3868)

* session: runtime api for generating session membership proofs

* grandpa: add runtime api for creating equivocation report txs

* grandpa: submit signed equivocation report transactions

* grandpa: use proper equivocation report type

* grandpa: report equivocations

* grandpa: validate equivocation proof

* grandpa: update to finality-grandpa 0.9.1

* grandpa: fix encoding of session membership proof

* grandpa: initialize set id session mapping for genesis session

* grandpa: fix bug in set_id session validation

* fix compilation

* cleanup from merge conflicts

* cleanup crate tomls

* grandpa: refactor equivocation handling to separate trait

* node-template: fix compilation

* fix test compilation

* bump finality-grandpa to v0.10.2

* rpc: fix runtime version test

* CHERRY-PICK #4200: Add documentation to SubmitSignedTransaction and actually make it work

Squashed commit of the following:

commit 4f2cb0b1c588a06f2f3b478bb4b28b5cb29d54b9
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Tue Dec 3 16:29:33 2019 +0100

    Split the method to avoid confusing type error message.

commit c5bf24eeaaf902add89ed1b046b22c4a4aaeb2cd
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Tue Dec 3 16:19:55 2019 +0100

    Make accounts optional, fix logic.

commit 97db1ef556e023cf6847e5ffdb036c0e3ea6fb0a
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Tue Dec 3 10:06:20 2019 +0100

    Remove warning.

commit 535f5c116d1a2e826eaf90c3f7e6798e443d61d8
Merge: 516257217 0f1a5f651
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Tue Dec 3 07:08:05 2019 +0100

    Merge branch 'master' into td-signed-transactions

commit 516257217bac89fcebd083712f4ea68b7b23b55a
Merge: ac98248c6 2e68c80c2
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Mon Dec 2 13:57:25 2019 +0100

    Merge branch 'master' into td-signed-transactions

commit ac98248c6c56cff381130645a82a13d29933cf83
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Mon Nov 25 17:34:52 2019 +0100

    Forgotten import.

commit 67a3c19031506c28e31c6bc4a90fff62d467dd58
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Mon Nov 25 17:32:10 2019 +0100

    Fix naming and bounds.

commit 93e768ea9df97a4629fca1f9bc4b108fdb33f876
Author: Tomasz Drwięga <tomasz@parity.io>
Date:   Mon Nov 25 17:01:05 2019 +0100

    Add documentation to signed transactions and actually make them work.

* grandpa: skip block initialization on report submission method

* primitives: allow transaction pool access by default for offchain calls

* grandpa: unused parameters

* grandpa: remove unused method

* grandpa: enable equivocation reporting

* grandpa: add workaround for parameter encoding

* grandpa: fix localized_payload calls in tests

* fix submit_report_equivocation_extrinsic in runtimes

* node: fix submit transaction test compilation

* node: bump spec_version

* rpc: fix api version test

* grandpa: allow custom equivocation offence type

* grandpa: add test for authorities::next_change_height

* grandpa: cleanup report_equivocation function

* node: move reporting app crypto to node-primitives

* grandpa: move equivocation traits to own module

* grandpa: rename app-crypto crate import

* grandpa: export equivocation types

* node: bump spec_version

* grandpa: rename EquivocationReport to EquivocationProof

* grandpa: add missing docs to primitives

* grandpa: add missing docs to equivocation

* node: fix compilation

* grandpa: add missing docs to pallet

* node: bump spec_version

* fix whitespace

* grandpa: return error on offence reporting

* grandpa: expose session and validator count in proofs through traits

* grandpa: use strong key in module KeyOwnerProofSystem

* grandpa: move key ownership proof to grandpa runtime api

* grandpa: remove unnecessary cloning when checking equivocation proof

* grandpa: make report_equivocation a method in Environment

* support: implement KeyOwnerProofSystem for ()

* grandpa: move KeyOwnerProofSystem to module trait

* test-utils: fix runtime compilation

* grandpa: fix test compilation

* grandpa: fix test compilation after merge

* grandpa: simplify transaction submission types

* grandpa: validate equivocation report in signed extension

* client: fix test

* node: use ValidateEquivocationReport signed extension

* grandpa: expose key ownership proof under opaque type

* grandpa: better docs on key ownership proofs

* grandpa: add note about signed extension

* grandpa: add ValidateEquivocationReport::new

* grandpa: remove skip_initialize_block from runtime api

* grandpa: use new offchain transaction submission API

* grandpa: take set_id in generate_key_ownership_proof

* grandpa: update to finality-grandpa v0.12.2

* grandpa: cleanup usages of AuthoritySet::current

* grandpa: fix test

* grandpa: add mocking utilities for equivocation reporting

* grandpa: add test for equivocation reporting

* grandpa: move SetIdSession initialization

* grandpa: add more tests

* node: enable historical session manager

* node: bump spec_version

* node: use strong key types in KeyOwnerProofSystem definitions

* grandpa: export GrandpaEquivocationOffence type

substrate/primitives/session/src/lib.rs

@@ -18,14 +18,17 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
-use sp_std::vec::Vec;
+use codec::{Encode, Decode};
 
 #[cfg(feature = "std")]
 use sp_runtime::{generic::BlockId, traits::Block as BlockT};
 #[cfg(feature = "std")]
 use sp_api::ProvideRuntimeApi;
 
+use sp_core::RuntimeDebug;
 use sp_core::crypto::KeyTypeId;
+use sp_staking::SessionIndex;
+use sp_std::vec::Vec;
 
 sp_api::decl_runtime_apis! {
 	/// Session keys runtime api.
@@ -46,6 +49,32 @@ sp_api::decl_runtime_apis! {
 	}
 }
 
+/// Number of validators in a given session.
+pub type ValidatorCount = u32;
+
+/// Proof of membership of a specific key in a given session.
+#[derive(Encode, Decode, Clone, Eq, PartialEq, Default, RuntimeDebug)]
+pub struct MembershipProof {
+	/// The session index on which the specific key is a member.
+	pub session: SessionIndex,
+	/// Trie nodes of a merkle proof of session membership.
+	pub trie_nodes: Vec<Vec<u8>>,
+	/// The validator count of the session on which the specific key is a member.
+	pub validator_count: ValidatorCount,
+}
+
+impl MembershipProof {
+	/// Returns a session this proof was generated for.
+	pub fn session(&self) -> SessionIndex {
+		self.session
+	}
+
+	/// Returns the validator count of the session this proof was generated for.
+	pub fn validator_count(&self) -> ValidatorCount {
+		self.validator_count
+	}
+}
+
 /// Generate the initial session keys with the given seeds, at the given block and store them in
 /// the client's keystore.
 #[cfg(feature = "std")]