Adding Bridges code as git subtree. (#2515)

* Add instructions.

* Squashed 'bridges/' content from commit 345e84a21

git-subtree-dir: bridges
git-subtree-split: 345e84a2146b56628e9888c9f5e129cb40e868a9

* Remove bridges workspace file to avoid confusing Cargo.

* Add some bridges primitives to Polkadot workspace.

* Improve docs.

polkadot/bridges/primitives/test-utils/src/lib.rs

@@ -0,0 +1,151 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common 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.
+
+// Parity Bridges Common 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 Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Utilities for testing runtime code.
+//!
+//! Unlike other crates in the `primitives` folder, this crate does *not* need to compile in a
+//! `no_std` environment. This is fine because this code should only be used, as the name implies,
+//! in tests.
+
+use bp_header_chain::justification::GrandpaJustification;
+use finality_grandpa::voter_set::VoterSet;
+use sp_finality_grandpa::{AuthorityId, AuthorityList, AuthorityWeight};
+use sp_finality_grandpa::{AuthoritySignature, SetId};
+use sp_keyring::Ed25519Keyring;
+use sp_runtime::traits::Header as HeaderT;
+use sp_runtime::traits::{One, Zero};
+
+pub const TEST_GRANDPA_ROUND: u64 = 1;
+pub const TEST_GRANDPA_SET_ID: SetId = 1;
+
+/// Get a valid Grandpa justification for a header given a Grandpa round, authority set ID, and
+/// authority list.
+pub fn make_justification_for_header<H: HeaderT>(
+	header: &H,
+	round: u64,
+	set_id: SetId,
+	authorities: &[(AuthorityId, AuthorityWeight)],
+) -> GrandpaJustification<H> {
+	let (target_hash, target_number) = (header.hash(), *header.number());
+	let mut precommits = vec![];
+	let mut votes_ancestries = vec![];
+
+	// We want to make sure that the header included in the vote ancestries
+	// is actually related to our target header
+	let mut precommit_header = test_header::<H>(target_number + One::one());
+	precommit_header.set_parent_hash(target_hash);
+
+	// I'm using the same header for all the voters since it doesn't matter as long
+	// as they all vote on blocks _ahead_ of the one we're interested in finalizing
+	for (id, _weight) in authorities.iter() {
+		let signer = extract_keyring(&id);
+		let precommit = signed_precommit::<H>(
+			signer,
+			(precommit_header.hash(), *precommit_header.number()),
+			round,
+			set_id,
+		);
+		precommits.push(precommit);
+		votes_ancestries.push(precommit_header.clone());
+	}
+
+	GrandpaJustification {
+		round,
+		commit: finality_grandpa::Commit {
+			target_hash,
+			target_number,
+			precommits,
+		},
+		votes_ancestries,
+	}
+}
+
+fn signed_precommit<H: HeaderT>(
+	signer: Ed25519Keyring,
+	target: (H::Hash, H::Number),
+	round: u64,
+	set_id: SetId,
+) -> finality_grandpa::SignedPrecommit<H::Hash, H::Number, AuthoritySignature, AuthorityId> {
+	let precommit = finality_grandpa::Precommit {
+		target_hash: target.0,
+		target_number: target.1,
+	};
+	let encoded =
+		sp_finality_grandpa::localized_payload(round, set_id, &finality_grandpa::Message::Precommit(precommit.clone()));
+	let signature = signer.sign(&encoded[..]).into();
+	finality_grandpa::SignedPrecommit {
+		precommit,
+		signature,
+		id: signer.public().into(),
+	}
+}
+
+/// Get a header for testing.
+///
+/// The correct parent hash will be used if given a non-zero header.
+pub fn test_header<H: HeaderT>(number: H::Number) -> H {
+	let mut header = H::new(
+		number,
+		Default::default(),
+		Default::default(),
+		Default::default(),
+		Default::default(),
+	);
+
+	if number != Zero::zero() {
+		let parent_hash = test_header::<H>(number - One::one()).hash();
+		header.set_parent_hash(parent_hash);
+	}
+
+	header
+}
+
+/// Convenience function for generating a Header ID at a given block number.
+pub fn header_id<H: HeaderT>(index: u8) -> (H::Hash, H::Number) {
+	(test_header::<H>(index.into()).hash(), index.into())
+}
+
+/// Get the identity of a test account given an ED25519 Public key.
+pub fn extract_keyring(id: &AuthorityId) -> Ed25519Keyring {
+	let mut raw_public = [0; 32];
+	raw_public.copy_from_slice(id.as_ref());
+	Ed25519Keyring::from_raw_public(raw_public).unwrap()
+}
+
+/// Get a valid set of voters for a Grandpa round.
+pub fn voter_set() -> VoterSet<AuthorityId> {
+	VoterSet::new(authority_list()).unwrap()
+}
+
+/// Convenience function to get a list of Grandpa authorities.
+pub fn authority_list() -> AuthorityList {
+	vec![(alice(), 1), (bob(), 1), (charlie(), 1)]
+}
+
+/// Get the Public key of the Alice test account.
+pub fn alice() -> AuthorityId {
+	Ed25519Keyring::Alice.public().into()
+}
+
+/// Get the Public key of the Bob test account.
+pub fn bob() -> AuthorityId {
+	Ed25519Keyring::Bob.public().into()
+}
+
+/// Get the Public key of the Charlie test account.
+pub fn charlie() -> AuthorityId {
+	Ed25519Keyring::Charlie.public().into()
+}