Add a build-sync-spec subcommand and remove the CHT roots from the light sync state. (#6999)

* Move subcommands from sc-cli to nodes

* Add --build-sync-spec subcommand

* Remove CHTs from snapshots

* Keep ProvideChtRoots

substrate/client/service/src/chain_ops/build_sync_spec.rs

@@ -0,0 +1,36 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+use sp_runtime::traits::Block as BlockT;
+use sp_blockchain::HeaderBackend;
+use std::sync::Arc;
+use sp_runtime::generic::BlockId;
+
+/// Build a `LightSyncState` from the CHT roots stored in a backend.
+pub fn build_light_sync_state<TBl, TCl>(
+	client: Arc<TCl>,
+) -> Result<sc_chain_spec::LightSyncState<TBl>, sp_blockchain::Error>
+	where
+		TBl: BlockT,
+		TCl: HeaderBackend<TBl>,
+{
+	let finalized_hash = client.info().finalized_hash;
+	let header = client.header(BlockId::Hash(finalized_hash))?.unwrap();
+
+	Ok(sc_chain_spec::LightSyncState {
+		header
+	})
+}