fix(datastore): decode optimistically with paginated list response type

Amplify/Categories/API/Response/GraphQLError.swift

@@ -44,3 +44,5 @@ extension GraphQLError {
         public let column: Int
     }
 }
+
+extension GraphQLError: Error { }

AmplifyPlugins/Core/AWSPluginsCore/Sync/PaginatedList.swift

@@ -12,4 +12,29 @@ public struct PaginatedList<ModelType: Model>: Decodable {
     public let items: [MutationSync<ModelType>]
     public let nextToken: String?
     public let startedAt: Int64?
+
+    enum CodingKeys: CodingKey {
+        case items
+        case nextToken
+        case startedAt
+    }
+
+    public init(from decoder: Decoder) throws {
+        let values = try decoder.container(keyedBy: CodingKeys.self)
+        let optimisticDecodedResults = try values.decode([OptimisticDecoded<MutationSync<ModelType>>].self, forKey: .items)
+        items = optimisticDecodedResults.compactMap { try? $0.result.get() }
+        nextToken = try values.decode(String?.self, forKey: .nextToken)
+        startedAt = try values.decode(Int64?.self, forKey: .startedAt)
+    }
+}
+
+
+fileprivate struct OptimisticDecoded<T: Decodable>: Decodable {
+    let result: Swift.Result<T, Error>
+
+    init(from decoder: Decoder) throws {
+        result = Result(catching: {
+            try T(from: decoder)
+        })
+    }
 }

AmplifyPlugins/DataStore/Sources/AWSDataStorePlugin/Sync/InitialSync/InitialSyncOperation.swift

@@ -216,11 +216,17 @@ final class InitialSyncOperation: AsynchronousOperation {
 
         let syncQueryResult: SyncQueryResult
         switch graphQLResult {
+        case .success(let queryResult):
+            syncQueryResult = queryResult
+
+        case .failure(.partial(let queryResult, let errors)):
+            syncQueryResult = queryResult
+            errors.map { DataStoreError.api(APIError(errorDescription: $0.message, error: $0)) }
+                .forEach { dataStoreConfiguration.errorHandler($0) }
+
         case .failure(let graphQLResponseError):
             finish(result: .failure(DataStoreError.api(graphQLResponseError)))
             return
-        case .success(let queryResult):
-            syncQueryResult = queryResult
         }
 
         let items = syncQueryResult.items