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

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

@@ -0,0 +1,83 @@
+// 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 quote::quote;
+use syn::Result;
+use syn::spanned::Spanned;
+
+use super::*;
+
+/// Generates the wrapper type enum.
+pub(crate) fn impl_message_wrapper_enum(info: &OverseerInfo) -> Result<proc_macro2::TokenStream> {
+	let consumes = info.consumes();
+	let consumes_variant = info.variant_names();
+
+	let outgoing = &info.outgoing_ty;
+
+	let message_wrapper = &info.message_wrapper;
+
+	let (outgoing_from_impl, outgoing_decl) = if let Some(outgoing) = outgoing {
+		let outgoing_variant = outgoing
+			.get_ident()
+			.ok_or_else(||{
+				syn::Error::new(outgoing.span(), "Missing identifier to use as enum variant for outgoing.")
+			})?;
+		(quote! {
+			impl ::std::convert::From< #outgoing > for #message_wrapper {
+				fn from(message: #outgoing) -> Self {
+					#message_wrapper :: #outgoing_variant ( message )
+				}
+			}
+		},
+		quote! {
+			#outgoing_variant ( #outgoing ) ,
+		})
+	} else {
+		(TokenStream::new(), TokenStream::new())
+	};
+
+	let ts = quote! {
+		/// Generated message type wrapper
+		#[allow(missing_docs)]
+		#[derive(Debug)]
+		pub enum #message_wrapper {
+			#(
+				#consumes_variant ( #consumes ),
+			)*
+			#outgoing_decl
+			// dummy message type
+			Empty,
+		}
+
+		impl ::std::convert::From< () > for #message_wrapper {
+			fn from(_: ()) -> Self {
+				#message_wrapper :: Empty
+			}
+		}
+
+		#(
+			impl ::std::convert::From< #consumes > for #message_wrapper {
+				fn from(message: #consumes) -> Self {
+					#message_wrapper :: #consumes_variant ( message )
+				}
+			}
+		)*
+
+		#outgoing_from_impl
+	};
+
+	Ok(ts)
+}