test: add unit test to catch missing distribution to subsystems faster (#2495)

* test: add unit test to catch missing distribution to subsystems faster

* add a simple count

* introduce proc macro to generate dispatch type

* refactor

* refactor

* chore: add license

* fixup unit test

* fixup merge

* better errors

* better fmt

* fix error spans

* better docs

* better error messages

* ui test foo

* Update node/subsystem/dispatch-gen/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/network/bridge/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/subsystem/Cargo.toml

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/subsystem/dispatch-gen/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/subsystem/dispatch-gen/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/network/bridge/src/lib.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

* fix compilation

* use find_map

* drop the silly 2, use _inner instead

* Update node/network/bridge/src/lib.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

* Update node/subsystem/dispatch-gen/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* nail deps down

* more into()

* flatten

* missing use statement

* fix messages order

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Andronik Ordian <write@reusable.software>

polkadot/node/subsystem/dispatch-gen/tests/ui/err-01-missing-skip.rs

@@ -0,0 +1,37 @@
+#![allow(dead_code)]
+
+use polkadot_procmacro_subsystem_dispatch_gen::subsystem_dispatch_gen;
+
+/// The event type in question.
+#[derive(Clone, Copy)]
+enum Event {
+	Smth,
+	Else,
+}
+
+impl Event {
+	fn focus(&self) -> std::result::Result<Inner, ()> {
+		unimplemented!("foo")
+	}
+}
+
+/// This should have a `From<Event>` impl but does not.
+#[derive(Clone)]
+enum Inner {
+	Foo,
+	Bar(Event),
+}
+
+#[subsystem_dispatch_gen(Event)]
+#[derive(Clone)]
+enum AllMessages {
+	/// Foo
+	Vvvvvv(Inner),
+
+    /// Missing a `#[skip]` annotation
+    Uuuuu,
+}
+
+fn main() {
+    let _x = AllMessages::dispatch_iter(Event::Else);
+}