graphql-alt: latest ProtocolConfigs

## Description

Fetch the latest protocol config in scope if no protocol version is
provided.

## Test plan

Update E2E tests:

```
sui$ cargo nextest run         \
  -p sui-indexer-alt-e2e-tests \
  -- graphql/epochs/protocol_configs
```

Author: amnn

crates/sui-indexer-alt-e2e-tests/tests/graphql/epochs/protocol_configs.move

@@ -27,6 +27,11 @@
   }
 }
 
+//# run-graphql
+{ # Latest protocol config
+  protocolConfigs { protocolVersion }
+}
+
 //# run-graphql
 { # Fetch protocol config version via epoch
   epoch(epochId: 0) { protocolConfigs { protocolVersion } }

crates/sui-indexer-alt-e2e-tests/tests/graphql/epochs/protocol_configs.snap

@@ -1,7 +1,7 @@
 ---
 source: external-crates/move/crates/move-transactional-test-runner/src/framework.rs
 ---
-processed 5 tasks
+processed 6 tasks
 
 init:
 A: object(0,0)
@@ -42,7 +42,17 @@ Response: {
   }
 }
 
-task 4, lines 30-36:
+task 4, lines 30-33:
+//# run-graphql
+Response: {
+  "data": {
+    "protocolConfigs": {
+      "protocolVersion": 70
+    }
+  }
+}
+
+task 5, lines 35-41:
 //# run-graphql
 Response: {
   "data": {

crates/sui-indexer-alt-graphql/schema.graphql

@@ -449,9 +449,9 @@ type Query {
 	"""
 	package(address: SuiAddress!, version: UInt53, atCheckpoint: UInt53): MovePackage
 	"""
-	Fetch the protocol config by protocol version.
+	Fetch the protocol config by protocol version, or the latest protocol config used on chain if no version is provided.
 	"""
-	protocolConfigs(version: UInt53!): ProtocolConfigs
+	protocolConfigs(version: UInt53): ProtocolConfigs
 	"""
 	Configuration for this RPC service.
 	"""

crates/sui-indexer-alt-graphql/src/api/query.rs

@@ -227,9 +227,18 @@ impl Query {
         .await
     }
 
-    /// Fetch the protocol config by protocol version.
-    async fn protocol_configs(&self, version: UInt53) -> Option<ProtocolConfigs> {
-        Some(ProtocolConfigs::with_protocol_version(version.into()))
+    /// Fetch the protocol config by protocol version, or the latest protocol config used on chain if no version is provided.
+    async fn protocol_configs(
+        &self,
+        ctx: &Context<'_>,
+        version: Option<UInt53>,
+    ) -> Result<Option<ProtocolConfigs>, RpcError> {
+        if let Some(version) = version {
+            Ok(Some(ProtocolConfigs::with_protocol_version(version.into())))
+        } else {
+            let scope = self.scope(ctx)?;
+            ProtocolConfigs::latest(ctx, &scope).await
+        }
     }
 
     /// Configuration for this RPC service.

crates/sui-indexer-alt-graphql/src/api/types/protocol_configs.rs

@@ -1,18 +1,18 @@
 // Copyright (c) Mysten Labs, Inc.
 // SPDX-License-Identifier: Apache-2.0
 
-use std::collections::BTreeMap;
+use std::{collections::BTreeMap, sync::Arc};
 
 use anyhow::Context as _;
-use async_graphql::{Context, Object, SimpleObject};
+use async_graphql::{dataloader::DataLoader, Context, Object, SimpleObject};
 use diesel::{ExpressionMethods, QueryDsl as _};
-use sui_indexer_alt_reader::pg_reader::PgReader;
+use sui_indexer_alt_reader::{epochs::CheckpointBoundedEpochStartKey, pg_reader::PgReader};
 use sui_indexer_alt_schema::{
     epochs::{StoredFeatureFlag, StoredProtocolConfig},
     schema::{kv_feature_flags, kv_protocol_configs},
 };
 
-use crate::{api::scalars::uint53::UInt53, error::RpcError};
+use crate::{api::scalars::uint53::UInt53, error::RpcError, scope::Scope};
 
 pub(crate) struct ProtocolConfigs {
     protocol_version: u64,
@@ -109,6 +109,24 @@ impl ProtocolConfigs {
     pub(crate) fn with_protocol_version(protocol_version: u64) -> Self {
         Self { protocol_version }
     }
+
+    /// Fetch the protocol config for the latest epoch in scope.
+    pub(crate) async fn latest(ctx: &Context<'_>, scope: &Scope) -> Result<Option<Self>, RpcError> {
+        let pg_loader: &Arc<DataLoader<PgReader>> = ctx.data()?;
+
+        let cp = scope.checkpoint_viewed_at();
+        let Some(stored) = pg_loader
+            .load_one(CheckpointBoundedEpochStartKey(cp))
+            .await
+            .context("Failed to fetch latest epoch")?
+        else {
+            return Ok(None);
+        };
+
+        Ok(Some(Self {
+            protocol_version: stored.protocol_version as u64,
+        }))
+    }
 }
 
 impl ConfigContent {

crates/sui-indexer-alt-graphql/src/snapshots/sui_indexer_alt_graphql__tests__schema.graphql.snap

@@ -453,9 +453,9 @@ type Query {
 	"""
 	package(address: SuiAddress!, version: UInt53, atCheckpoint: UInt53): MovePackage
 	"""
-	Fetch the protocol config by protocol version.
+	Fetch the protocol config by protocol version, or the latest protocol config used on chain if no version is provided.
 	"""
-	protocolConfigs(version: UInt53!): ProtocolConfigs
+	protocolConfigs(version: UInt53): ProtocolConfigs
 	"""
 	Configuration for this RPC service.
 	"""

crates/sui-indexer-alt-graphql/src/snapshots/sui_indexer_alt_graphql__tests__staging.graphql.snap

@@ -453,9 +453,9 @@ type Query {
 	"""
 	package(address: SuiAddress!, version: UInt53, atCheckpoint: UInt53): MovePackage
 	"""
-	Fetch the protocol config by protocol version.
+	Fetch the protocol config by protocol version, or the latest protocol config used on chain if no version is provided.
 	"""
-	protocolConfigs(version: UInt53!): ProtocolConfigs
+	protocolConfigs(version: UInt53): ProtocolConfigs
 	"""
 	Configuration for this RPC service.
 	"""

crates/sui-indexer-alt-graphql/staging.graphql

@@ -449,9 +449,9 @@ type Query {
 	"""
 	package(address: SuiAddress!, version: UInt53, atCheckpoint: UInt53): MovePackage
 	"""
-	Fetch the protocol config by protocol version.
+	Fetch the protocol config by protocol version, or the latest protocol config used on chain if no version is provided.
 	"""
-	protocolConfigs(version: UInt53!): ProtocolConfigs
+	protocolConfigs(version: UInt53): ProtocolConfigs
 	"""
 	Configuration for this RPC service.
 	"""