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/lib.rs

@@ -0,0 +1,46 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// 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 Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Cross-Consensus Message format data structures.
+
+// NOTE, this crate is meant to be used in many different environments, notably wasm, but not
+// necessarily related to FRAME or even Substrate.
+//
+// Hence, `no_std` rather than sp-runtime.
+#![no_std]
+extern crate alloc;
+
+use codec::{Encode, Decode};
+
+pub mod v0;
+
+/// A single XCM message, together with its version code.
+#[derive(Clone, Eq, PartialEq, Encode, Decode, Debug)]
+pub enum VersionedXcm {
+	V0(v0::Xcm),
+}
+
+/// A versioned multi-location, a relative location of a cross-consensus system identifier.
+#[derive(Clone, Eq, PartialEq, Encode, Decode, Debug)]
+pub enum VersionedMultiLocation {
+	V0(v0::MultiLocation),
+}
+
+/// A versioned multi-asset, an identifier for an asset within a consensus system.
+#[derive(Clone, Eq, PartialEq, Encode, Decode, Debug)]
+pub enum VersionedMultiAsset {
+	V0(v0::MultiAsset),
+}