cob/change_graph: Log Errors

In case of a signature verification failure or failure to apply an
operation, the error is swallowed, but not logged.

During debugging, it can be crucial to understand whether these errors
occur, so log them.

If trace logging is enabled, also log the tips that are used. This
gives a better overview where operations originate from.

crates/radicle-cob/src/change_graph.rs

@@ -39,12 +39,18 @@ impl ChangeGraph {
     where
         S: change::Storage<ObjectId = Oid, Parent = Oid, Signatures = ExtendedSignature>,
     {
-        log::debug!(target: "cob", "Loading object of type {typename} at {oid}");
+        let tip_refs = tip_refs.collect::<Vec<_>>();
+
+        if log::log_enabled!(log::Level::Debug) {
+            log::debug!(target: "cob", "Loading object of type {typename} at {oid}.");
+        } else if log::log_enabled!(log::Level::Trace) {
+            log::trace!(target: "cob", "Loading object of type {typename} at {oid} from tips {}.", tip_refs.iter().map(|r| r.to_string()).collect::<Vec<_>>().join(", "));
+        }
 
         let mut graph: Dag<Oid, Entry> = Dag::new();
 
         // Populate the initial set of node ids from the refs we have
-        let mut child_ids = Vec::from_iter(tip_refs.map(|r| r.target.id));
+        let mut child_ids = Vec::from_iter(tip_refs.into_iter().map(|r| r.target.id));
         let mut edges_to_add = Vec::new();
 
         while let Some(child_id) = child_ids.pop() {
@@ -113,13 +119,12 @@ impl ChangeGraph {
             |_, entry, siblings| {
                 // Check the entry signatures are valid.
                 if !entry.valid_signatures() {
+                    log::debug!("Signature verification failed for entry {}.", entry.id);
                     return ControlFlow::Break(());
                 }
-                // Apply the entry to the state, and if there's an error, prune that branch.
-                if object
-                    .apply(entry, siblings.map(|(k, n)| (k, &n.value)), store)
-                    .is_err()
-                {
+                // Apply the entry to the state, and if there is an error, prune that branch.
+                if let Err(err) = object.apply(entry, siblings.map(|(k, n)| (k, &n.value)), store) {
+                    log::debug!("Application of entry {} returned error: {err}", entry.id);
                     return ControlFlow::Break(());
                 }
                 ControlFlow::Continue(())

crates/radicle-cob/src/object/storage.rs

@@ -45,6 +45,12 @@ pub struct Reference {
     pub target: Commit,
 }
 
+impl std::fmt::Display for Reference {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{} @ {}", self.name, self.target.id)
+    }
+}
+
 /// A [`Commit`] that holds the data for a given [`crate::CollaborativeObject`].
 #[derive(Clone, Debug)]
 pub struct Commit {