feat(gateway): Make resharding.getSessionInfo optional (#3854)

* Make getSessionInfo optional

* change resharding.getSessionInfo to throw in checkIfReshardingIsNeeded

* Change warn message on spawnShards

packages/gateway/src/manager.ts

@@ -60,11 +60,6 @@ export function createGatewayManager(options: CreateGatewayManagerOptions): Gate
       checkInterval: 28800000, // 8 hours
       shards: new Collection(),
       pendingShards: new Collection(),
-      async getSessionInfo() {
-        throw new Error(
-          '[Resharding] was enabled but no getSessionInfo handler was provided. Please set a handler like: gateway.resharding.getSessionInfo = async () => { // insert code here to fetch getSessionInfo from rest process. }',
-        )
-      },
       async checkIfReshardingIsNeeded() {
         gateway.logger.warn('[Resharding] Checking if resharding is needed.')
 
@@ -74,6 +69,10 @@ export function createGatewayManager(options: CreateGatewayManagerOptions): Gate
           return { needed: false }
         }
 
+        if (!gateway.resharding.getSessionInfo) {
+          throw new Error("[Resharding] Resharding is enabled but no 'resharding.getSessionInfo()' is not provided.")
+        }
+
         gateway.logger.warn('[Resharding] Resharding is enabled.')
 
         const sessionInfo = await gateway.resharding.getSessionInfo()
@@ -328,6 +327,13 @@ export function createGatewayManager(options: CreateGatewayManagerOptions): Gate
         // It is better to ensure there is always only one
         clearInterval(gateway.resharding.checkIntervalId)
 
+        if (!gateway.resharding.getSessionInfo) {
+          gateway.resharding.enabled = false
+          gateway.logger.warn("[Resharding] Resharding is enabled but 'resharding.getSessionInfo()' was not provided. Disabling resharding.")
+
+          return
+        }
+
         gateway.resharding.checkIntervalId = setInterval(async () => {
           const reshardingInfo = await gateway.resharding.checkIfReshardingIsNeeded()
 
@@ -688,7 +694,7 @@ export interface GatewayManager extends Required<CreateGatewayManagerOptions> {
     /** Holds the pending shards that have been created and are pending all shards finish loading. */
     pendingShards: Collection<number, Shard>
     /** Handler to get shard count and other session info. */
-    getSessionInfo: () => Promise<Camelize<DiscordGetGatewayBot>>
+    getSessionInfo?: () => Promise<Camelize<DiscordGetGatewayBot>>
     /** Handler to edit the shard id on any cached guilds. */
     updateGuildsShardId: (guildIds: string[], shardId: number) => Promise<void>
     /** Handler to check if resharding is necessary. */