impl ProvideInherent for InclusionInherent (#1318)

* impl ProvideInherent for InclusionInherent

* reduce import churn; correct expect message

* move inclusion inherent identifier into primitives

It's not clear precisely why this is desired, but it's a pattern
I've seen in several places, so I'm going this to be on the
safe side. Worst case, we can revert this commit pretty easily.

* bump kusama spec_version to placate CI

* add license header

* empty commit; maybe github will notice the one with changes

* add sanity check to only include valid inherents

primitives/src/inclusion_inherent.rs

@@ -0,0 +1,23 @@
+// Copyright 2017-2020 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot 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.
+
+// Polkadot 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 Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Inclusion Inherent primitives define types and constants which can be imported
+//! without needing to import the entire inherent module.
+
+use inherents::InherentIdentifier;
+
+/// Unique identifier for the Inclusion Inherent
+pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"inclusn0";

primitives/src/lib.rs

@@ -23,6 +23,7 @@
 use runtime_primitives::{generic, MultiSignature};
 pub use runtime_primitives::traits::{BlakeTwo256, Hash as HashT, Verify, IdentifyAccount};
 
+pub mod inclusion_inherent;
 pub mod parachain;
 
 pub use parity_scale_codec::Compact;

primitives/src/parachain.rs

@@ -722,6 +722,12 @@ pub type SignedAvailabilityBitfield = Signed<AvailabilityBitfield>;
 #[derive(Encode, Decode, Clone, PartialEq, Eq, RuntimeDebug)]
 pub struct SignedAvailabilityBitfields(pub Vec<SignedAvailabilityBitfield>);
 
+impl From<Vec<SignedAvailabilityBitfield>> for SignedAvailabilityBitfields {
+	fn from(fields: Vec<SignedAvailabilityBitfield>) -> SignedAvailabilityBitfields {
+		SignedAvailabilityBitfields(fields)
+	}
+}
+
 /// A backed (or backable, depending on context) candidate.
 // TODO: yes, this is roughly the same as AttestedCandidate.
 // After https://github.com/paritytech/polkadot/issues/1250

runtime/parachains/src/inclusion_inherent.rs

@@ -23,18 +23,23 @@
 
 use sp_std::prelude::*;
 use primitives::{
+	inclusion_inherent,
 	parachain::{BackedCandidate, SignedAvailabilityBitfields},
 };
 use frame_support::{
-	decl_storage, decl_module, decl_error, ensure,
+	decl_error, decl_module, decl_storage, ensure,
 	dispatch::DispatchResult,
 	weights::{DispatchClass, Weight},
 	traits::Get,
 };
 use system::ensure_none;
-use crate::{inclusion, scheduler::{self, FreedReason}};
+use crate::{
+	inclusion,
+	scheduler::{self, FreedReason},
+};
+use inherents::{InherentIdentifier, InherentData, MakeFatalError, ProvideInherent};
 
-pub trait Trait: inclusion::Trait + scheduler::Trait { }
+pub trait Trait: inclusion::Trait + scheduler::Trait {}
 
 decl_storage! {
 	trait Store for Module<T: Trait> as ParaInclusionInherent {
@@ -118,3 +123,23 @@ decl_module! {
 		}
 	}
 }
+
+impl<T: Trait> ProvideInherent for Module<T> {
+	type Call = Call<T>;
+	type Error = MakeFatalError<()>;
+	const INHERENT_IDENTIFIER: InherentIdentifier = inclusion_inherent::INHERENT_IDENTIFIER;
+
+	fn create_inherent(data: &InherentData) -> Option<Self::Call> {
+		data.get_data(&Self::INHERENT_IDENTIFIER)
+			.expect("inclusion inherent data failed to decode")
+			.map(|(signed_bitfields, backed_candidates): (SignedAvailabilityBitfields, Vec<BackedCandidate<T::Hash>>)| {
+				// Sanity check: session changes can invalidate an inherent, and we _really_ don't want that to happen.
+				// See github.com/paritytech/polkadot/issues/1327
+				if Self::inclusion(system::RawOrigin::None.into(), signed_bitfields.clone(), backed_candidates.clone()).is_ok() {
+					Call::inclusion(signed_bitfields, backed_candidates)
+				} else {
+					Call::inclusion(Vec::new().into(), Vec::new())
+				}
+			})
+	}
+}