add an error message if some messages are lopsided

If a message type is never sent or never received,
this leads to From<$ty> implementations being missing.

The implementation here adds a check and throws and error
pointint to the messages.

Closes #13

orchestra/proc-macro/Cargo.toml

@@ -14,9 +14,9 @@ targets = ["x86_64-unknown-linux-gnu"]
 proc-macro = true
 
 [dependencies]
-syn = { version = "1.0.95", features = ["full", "extra-traits"] }
+syn = { version = "1.0.105", features = ["full", "extra-traits"] }
 quote = "1.0.20"
-proc-macro2 = "1.0.43"
+proc-macro2 = { version = "1.0.47", features = ["span-locations"] }
 proc-macro-crate = "1.1.3"
 expander = { version = "0.0.6", default-features = false }
 petgraph = "0.6.0"

orchestra/proc-macro/src/impl_message_wrapper.rs

@@ -13,6 +13,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::collections::HashSet;
+
+use itertools::Itertools;
 use quote::quote;
 use syn::{spanned::Spanned, Result};
 
@@ -50,7 +53,7 @@ pub(crate) fn impl_message_wrapper_enum(info: &OrchestraInfo) -> Result<proc_mac
 		(TokenStream::new(), TokenStream::new())
 	};
 
-	let ts = quote! {
+	let mut ts = quote! {
 		/// Generated message type wrapper over all possible messages
 		/// used by any subsystem.
 		#[allow(missing_docs)]
@@ -81,5 +84,51 @@ pub(crate) fn impl_message_wrapper_enum(info: &OrchestraInfo) -> Result<proc_mac
 		#outgoing_from_impl
 	};
 
+	// TODO it's not perfect, if the same type is used with different paths
+	// the detection will fail
+	let outgoing = HashSet::<&Path>::from_iter(
+		info.subsystems().iter().map(|ssf| ssf.messages_to_send.iter()).flatten(),
+	);
+	let incoming =
+		HashSet::<&Path>::from_iter(info.subsystems().iter().map(|ssf| &ssf.message_to_consume));
+
+	// Try to maintain the ordering according to the span start in the declaration.
+	fn cmp<'p, 'q>(a: &'p &&Path, b: &'q &&Path) -> std::cmp::Ordering {
+		a.span()
+			.start()
+			.partial_cmp(&b.span().start())
+			.unwrap_or(std::cmp::Ordering::Equal)
+	}
+
+	// sent but not received
+	for sbnr in outgoing.difference(&incoming).sorted_by(cmp) {
+		ts.extend(
+			syn::Error::new(
+				sbnr.span(),
+				format!(
+					"Message {} is sent but never received",
+					sbnr.get_ident()
+						.expect("Message is a path that must end in an identifier. qed")
+				),
+			)
+			.to_compile_error(),
+		);
+	}
+
+	// received but not sent
+	for rbns in incoming.difference(&outgoing).sorted_by(cmp) {
+		ts.extend(
+			syn::Error::new(
+				rbns.span(),
+				format!(
+					"Message {} is received but never sent",
+					rbns.get_ident()
+						.expect("Message is a path that must end in an identifier. qed")
+				),
+			)
+			.to_compile_error(),
+		);
+	}
+
 	Ok(ts)
 }