persist: tweak Display and Debug formatting of ids

All three of shard, writer, and reader start with unique letters, so add
the letter to the beginning of the Display impl so they can easily be
distinguished. Also manually implement the Debug impl so it prints like
a UUID instead of the raw bytes.

Author: danhhz

src/persist-client/src/lib.rs

@@ -112,12 +112,18 @@ impl Location {
 }
 
 /// An opaque identifier for a persist durable TVC (aka shard).
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Deserialize, Serialize)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Deserialize, Serialize)]
 pub struct ShardId([u8; 16]);
 
 impl std::fmt::Display for ShardId {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Display::fmt(&Uuid::from_bytes(self.0), f)
+        write!(f, "s{}", Uuid::from_bytes(self.0))
+    }
+}
+
+impl std::fmt::Debug for ShardId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "ShardId({})", Uuid::from_bytes(self.0))
     }
 }
 
@@ -414,4 +420,32 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn fmt_ids() {
+        assert_eq!(
+            format!("{}", ShardId([0u8; 16])),
+            "s00000000-0000-0000-0000-000000000000"
+        );
+        assert_eq!(
+            format!("{:?}", ShardId([0u8; 16])),
+            "ShardId(00000000-0000-0000-0000-000000000000)"
+        );
+        assert_eq!(
+            format!("{}", WriterId([0u8; 16])),
+            "w00000000-0000-0000-0000-000000000000"
+        );
+        assert_eq!(
+            format!("{:?}", WriterId([0u8; 16])),
+            "WriterId(00000000-0000-0000-0000-000000000000)"
+        );
+        assert_eq!(
+            format!("{}", ReaderId([0u8; 16])),
+            "r00000000-0000-0000-0000-000000000000"
+        );
+        assert_eq!(
+            format!("{:?}", ReaderId([0u8; 16])),
+            "ReaderId(00000000-0000-0000-0000-000000000000)"
+        );
+    }
 }

src/persist-client/src/read.rs

@@ -32,12 +32,18 @@ use crate::r#impl::machine::Machine;
 use crate::ShardId;
 
 /// An opaque identifier for a reader of a persist durable TVC (aka shard).
-#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct ReaderId(pub(crate) [u8; 16]);
 
 impl std::fmt::Display for ReaderId {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Display::fmt(&Uuid::from_bytes(self.0), f)
+        write!(f, "r{}", Uuid::from_bytes(self.0))
+    }
+}
+
+impl std::fmt::Debug for ReaderId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "ReaderId({})", Uuid::from_bytes(self.0))
     }
 }
 

src/persist-client/src/write.rs

@@ -36,12 +36,18 @@ use crate::r#impl::machine::Machine;
 /// Deserialize. It's difficult to reason about the behavior if multiple writers
 /// accidentally end up concurrently using the same [WriterId] and we haven't
 /// (yet) found a need for it.
-#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct WriterId(pub(crate) [u8; 16]);
 
 impl std::fmt::Display for WriterId {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Display::fmt(&Uuid::from_bytes(self.0), f)
+        write!(f, "w{}", Uuid::from_bytes(self.0))
+    }
+}
+
+impl std::fmt::Debug for WriterId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "WriterId({})", Uuid::from_bytes(self.0))
     }
 }