Add the XCM primitives crate. (#1760)

Co-authored-by: Gavin Wood <gavin@parity.io>

Co-authored-by: Gavin Wood <gavin@parity.io>

polkadot/xcm/src/v0/junction.rs

@@ -0,0 +1,101 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Cumulus.
+
+// Substrate 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.
+
+// Substrate 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 Cumulus.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Support datastructures for `MultiLocation`, primarily the `Junction` datatype.
+
+use alloc::vec::Vec;
+use codec::{self, Encode, Decode};
+
+/// A global identifier of an account-bearing consensus system.
+#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Encode, Decode, Debug)]
+pub enum NetworkId {
+	/// Unidentified/any.
+	Any,
+	/// Some named network.
+	Named(Vec<u8>),
+	/// The Polkadot Relay chain
+	Polkadot,
+	/// Kusama.
+	Kusama,
+}
+
+/// A single item in a path to describe the relative location of a consensus system.
+///
+/// Each item assumes a pre-existing location as its context and is defined in terms of it.
+#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Encode, Decode, Debug)]
+pub enum Junction {
+	/// The consensus system of which the context is a member and state-wise super-set.
+	///
+	/// NOTE: This item is *not* a sub-consensus item: a consensus system may not identify itself trustlessly as
+	/// a location that includes this junction.
+	Parent,
+	/// An indexed parachain belonging to and operated by the context.
+	///
+	/// Generally used when the context is a Polkadot Relay-chain.
+	Parachain { #[codec(compact)] id: u32 },
+	/// A 32-byte identifier for an account of a specific network that is respected as a sovereign endpoint within
+	/// the context.
+	///
+	/// Generally used when the context is a Substrate-based chain.
+	AccountId32 { network: NetworkId, id: [u8; 32] },
+	/// An 8-byte index for an account of a specific network that is respected as a sovereign endpoint within
+	/// the context.
+	///
+	/// May be used when the context is a Frame-based chain and includes e.g. an indices pallet.
+	AccountIndex64 { network: NetworkId, #[codec(compact)] index: u64 },
+	/// A 20-byte identifier for an account of a specific network that is respected as a sovereign endpoint within
+	/// the context.
+	///
+	/// May be used when the context is an Ethereum or Bitcoin chain or smart-contract.
+	AccountKey20 { network: NetworkId, key: [u8; 20] },
+	/// An instanced, indexed pallet that forms a constituent part of the context.
+	///
+	/// Generally used when the context is a Frame-based chain.
+	PalletInstance { id: u8 },
+	/// A non-descript index within the context location.
+	///
+	/// Usage will vary widely owing to its generality.
+	///
+	/// NOTE: Try to avoid using this and instead use a more specific item.
+	GeneralIndex { #[codec(compact)] id: u128 },
+	/// A nondescript datum acting as a key within the context location.
+	///
+	/// Usage will vary widely owing to its generality.
+	///
+	/// NOTE: Try to avoid using this and instead use a more specific item.
+	GeneralKey(Vec<u8>),
+	/// The unambiguous child.
+	///
+	/// Not currently used except as a fallback when deriving ancestry.
+	OnlyChild,
+}
+
+impl Junction {
+	pub fn is_sub_consensus(&self) -> bool {
+		match self {
+			Junction::Parent => false,
+
+			Junction::Parachain { .. } |
+			Junction::AccountId32 { .. } |
+			Junction::AccountIndex64 { .. } |
+			Junction::AccountKey20 { .. } |
+			Junction::PalletInstance { .. } |
+			Junction::GeneralIndex { .. } |
+			Junction::GeneralKey(..) |
+			Junction::OnlyChild => true,
+		}
+	}
+}