refactor overseer into proc-macro based pattern (#2962)

polkadot/node/overseer/overseer-gen/proc-macro/src/impl_dispatch.rs

@@ -0,0 +1,70 @@
+// Copyright 2021 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/>.
+
+use super::*;
+use proc_macro2::{TokenStream, Ident};
+use quote::quote;
+use syn::Path;
+
+pub(crate) fn impl_dispatch(info: &OverseerInfo) -> TokenStream {
+	let message_wrapper = &info.message_wrapper;
+
+	let dispatchable_variant = info
+		.subsystems()
+		.into_iter()
+		.filter(|ssf| !ssf.no_dispatch)
+		.filter(|ssf| !ssf.wip)
+		.map(|ssf| ssf.generic.clone())
+		.collect::<Vec<Ident>>();
+
+	let dispatchable_message = info
+		.subsystems()
+		.into_iter()
+		.filter(|ssf| !ssf.no_dispatch)
+		.filter(|ssf| !ssf.wip)
+		.map(|ssf| ssf.consumes.clone())
+		.collect::<Vec<Path>>();
+
+	let mut ts = TokenStream::new();
+	if let Some(extern_network_ty) = &info.extern_network_ty.clone() {
+		ts.extend(quote! {
+			impl #message_wrapper {
+				/// Generated dispatch iterator generator.
+				pub fn dispatch_iter(extern_msg: #extern_network_ty) -> impl Iterator<Item=Self> + Send {
+					::std::array::IntoIter::new([
+					#(
+						extern_msg
+							// focuses on a `NetworkBridgeEvent< protocol_v1::* >`
+							// TODO do not require this to be hardcoded, either externalize or ...
+							// https://github.com/paritytech/polkadot/issues/3427
+							.focus()
+							.ok()
+							.map(|event| {
+								#message_wrapper :: #dispatchable_variant (
+									// the inner type of the enum variant
+									#dispatchable_message :: from( event )
+								)
+							}),
+					)*
+					])
+					.into_iter()
+					.filter_map(|x: Option<_>| x)
+				}
+			}
+		});
+	}
+	ts
+}