Add PluginDeclaration trait

This trait simplifies a lot of the message calls in the PluginBuilder.

Advantages: You only declare a list of handled messages _once_. This is
necessary since Rust does not allow 'queries' for types (aka "give me a
tuple of supported types" does not exist), and so the necessary crutch
is to declare them manually.

Disadvantages: You cannot pick at Runtime anymore what messages you
decide to support. This is considered to be a very niche use-case and
might actually be an anti-pattern.

Signed-off-by: Marcel Müller <m.mueller@ifm.com>

1 files changed, 14 insertions, 5 deletions

diff --git a/crates/core/tedge_api/examples/heartbeat.rs b/crates/core/tedge_api/examples/heartbeat.rs
index 15793bfc..7fae395e 100644
--- a/crates/core/tedge_api/examples/heartbeat.rs
+++ b/crates/core/tedge_api/examples/heartbeat.rs
@@ -9,8 +9,9 @@ use futures::FutureExt;
 use tedge_api::{
     address::ReplySender,
     message::NoReply,
-    plugin::{BuiltPlugin, Handle, HandleTypes, Message, PluginExt},
-    Address, Plugin, PluginBuilder, PluginConfiguration, PluginDirectory, PluginError, CancellationToken,
+    plugin::{BuiltPlugin, Handle, HandleTypes, Message, PluginDeclaration, PluginExt},
+    Address, CancellationToken, Plugin, PluginBuilder, PluginConfiguration, PluginDirectory,
+    PluginError,
 };
 
 /// A message that represents a heartbeat that gets sent to plugins
@@ -78,7 +79,7 @@ impl<PD: PluginDirectory> PluginBuilder<PD> for HeartbeatServiceBuilder {
             monitored_services,
             cancellation_token,
         )
-        .into_untyped::<()>())
+        .into_untyped())
     }
 }
 
@@ -96,6 +97,10 @@ struct HeartbeatService {
     cancel_token: CancellationToken,
 }
 
+impl PluginDeclaration for HeartbeatService {
+    type HandledMessages = ();
+}
+
 #[async_trait]
 impl Plugin for HeartbeatService {
     /// The setup function of the HeartbeatService can be used by the plugin author to setup for
@@ -203,7 +208,7 @@ impl<PD: PluginDirectory> PluginBuilder<PD> for CriticalServiceBuilder {
     where
         Self: Sized,
     {
-        HandleTypes::declare_handlers_for::<(Heartbeat,), CriticalService>()
+        CriticalService::get_handled_types()
     }
 
     async fn verify_configuration(
@@ -225,7 +230,7 @@ impl<PD: PluginDirectory> PluginBuilder<PD> for CriticalServiceBuilder {
         Ok(CriticalService {
             status: tokio::sync::Mutex::new(true),
         }
-        .into_untyped::<(Heartbeat,)>())
+        .into_untyped())
     }
 }
 
@@ -259,6 +264,10 @@ impl Handle<Heartbeat> for CriticalService {
     }
 }
 
+impl PluginDeclaration for CriticalService {
+    type HandledMessages = (Heartbeat,);
+}
+
 /// Because the CriticalService is of course a Plugin, it needs an implementation for that as well.
 #[async_trait]
 impl Plugin for CriticalService {