From 3b83c932c54ef62a9081ff92f23f68f7548cce2a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Joel=20H=C3=B6ner?= <joel@zystem.io>
Date: Sat, 28 Dec 2024 15:28:14 +0100
Subject: [PATCH 1/2] scylla: add working `Debug` impl for caching session

The previous derived implementation was not actually usable because
it had `Debug` bounds on the type parameters. The `RandomState` default
value for the `S` argument does not impl `Debug`, so this didn't work.

This commit switches to a manual `Debug` impl that doesn't have these
unnecessary bounds.
---
 scylla/src/transport/caching_session.rs | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/scylla/src/transport/caching_session.rs b/scylla/src/transport/caching_session.rs
index 77668b28c..debf0def6 100644
--- a/scylla/src/transport/caching_session.rs
+++ b/scylla/src/transport/caching_session.rs
@@ -16,6 +16,7 @@ use scylla_cql::frame::response::result::{PreparedMetadata, ResultMetadata};
 use scylla_cql::types::serialize::batch::BatchValues;
 use scylla_cql::types::serialize::row::SerializeRow;
 use std::collections::hash_map::RandomState;
+use std::fmt;
 use std::hash::BuildHasher;
 use std::sync::Arc;
 
@@ -39,7 +40,6 @@ struct RawPreparedStatementData {
 }
 
 /// Provides auto caching while executing queries
-#[derive(Debug)]
 pub struct GenericCachingSession<DeserializationApi, S = RandomState>
 where
     S: Clone + BuildHasher,
@@ -53,6 +53,20 @@ where
     cache: DashMap<String, RawPreparedStatementData, S>,
 }
 
+impl<DeserializationApi, S> fmt::Debug for GenericCachingSession<DeserializationApi, S>
+where
+    S: Clone + BuildHasher,
+    DeserializationApi: DeserializationApiKind,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("GenericCachingSession")
+            .field("session", &self.session)
+            .field("max_capacity", &self.max_capacity)
+            .field("cache", &self.cache)
+            .finish()
+    }
+}
+
 pub type CachingSession<S = RandomState> = GenericCachingSession<CurrentDeserializationApi, S>;
 
 #[deprecated(

From dc2e939ee847b1b5ba89ebe662aae89e84f3a9dd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Joel=20H=C3=B6ner?= <joel@zystem.io>
Date: Sat, 28 Dec 2024 15:41:19 +0100
Subject: [PATCH 2/2] scylla: static assert ensuring caching session impls
 `Debug`

---
 scylla/src/transport/caching_session.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/scylla/src/transport/caching_session.rs b/scylla/src/transport/caching_session.rs
index debf0def6..a5b641683 100644
--- a/scylla/src/transport/caching_session.rs
+++ b/scylla/src/transport/caching_session.rs
@@ -349,6 +349,8 @@ mod tests {
     use crate::transport::partitioner::PartitionerName;
     use crate::transport::session::Session;
     use crate::utils::test_utils::unique_keyspace_name;
+    #[allow(deprecated)]
+    use crate::LegacyCachingSession;
     use crate::{
         batch::{Batch, BatchStatement},
         prepared_statement::PreparedStatement,
@@ -780,4 +782,12 @@ mod tests {
         verify_partitioner().await;
         verify_partitioner().await;
     }
+
+    // NOTE: intentionally no `#[test]`: this is a compile-time test
+    fn _caching_session_impls_debug() {
+        fn assert_debug<T: std::fmt::Debug>() {}
+        assert_debug::<CachingSession>();
+        #[allow(deprecated)]
+        assert_debug::<LegacyCachingSession>();
+    }
 }