Use base-36 change tags in MockCloudDatabase

Sources/SQLiteData/CloudKit/CloudKit+StructuredQueries.swift

@@ -58,7 +58,7 @@
       if isTesting {
         queryOutput._recordChangeTag =
           coder
-          .decodeObject(of: NSNumber.self, forKey: "_recordChangeTag")?.intValue
+          .decodeObject(of: NSString.self, forKey: "_recordChangeTag") as String?
         queryOutput._modificationDate =
           coder
           .decodeObject(of: NSDate.self, forKey: "_modificationDate") as Date?
@@ -111,7 +111,7 @@
       if isTesting {
         queryOutput._recordChangeTag =
           coder
-          .decodeObject(of: NSNumber.self, forKey: "_recordChangeTag")?.intValue
+          .decodeObject(of: NSString.self, forKey: "_recordChangeTag") as String?
         queryOutput._modificationDate =
           coder
           .decodeObject(of: NSDate.self, forKey: "_modificationDate") as Date?
@@ -397,7 +397,7 @@
   private struct Unbindable: Error {}
 
   extension CKRecord {
-    package var _recordChangeTag: Int? {
+    package var _recordChangeTag: String? {
       get { self[#function] }
       set { self[#function] = newValue }
     }

Sources/SQLiteData/CloudKit/Internal/MockCloudDatabase.swift

@@ -15,7 +15,7 @@
     let clock: AnyClock<Duration>
 
     package struct State {
-      private var lastRecordChangeTag = 0
+      private var changeTagCounter = 0
       package var storage: [CKRecordZone.ID: Zone] = [:]
       var assets: [AssetID: Data] = [:]
       var deletedRecords: [(CKRecord.ID, CKRecord.RecordType)] = []
@@ -24,9 +24,9 @@
       package var rateLimitDuration: Duration
       fileprivate var requestTimestamps: [AnyClock<Duration>.Instant] = []
       package var fetchedRecordIDs: [CKRecord.ID] = []
-      mutating func nextRecordChangeTag() -> Int {
-        lastRecordChangeTag += 1
-        return lastRecordChangeTag
+      mutating func nextRecordChangeTag() -> String {
+        defer { changeTagCounter += 1 }
+        return String(changeTagCounter, radix: 36)
       }
       init(
         quota: Int = .max,

Sources/SQLiteData/CloudKit/Internal/MockSyncEngine.swift

@@ -45,17 +45,18 @@
       }
 
       modifications = state.withState { syncEngineState in
-        let currentChangeTag = syncEngineState.changeTag
+        let currentChangeTag = syncEngineState.currentChangeTag
         return database.state.withValue { dbState in
           zoneIDs.reduce(into: [CKRecord]()) { accum, zoneID in
             accum += ((dbState.storage[zoneID]?.records.values).map { Array($0) } ?? [])
               .map { $0.copy() as! CKRecord }
               .filter {
-                precondition(
-                  $0._recordChangeTag != nil,
-                  "Records stored in database should have their 'recordChangeTag' assigned."
-                )
-                return $0._recordChangeTag! > currentChangeTag
+                guard let changeTag = $0._recordChangeTag else {
+                  fatalError(
+                    "Records stored in database should have their 'recordChangeTag' assigned."
+                  )
+                }
+                return changeTag.isNewerChangeTag(than: currentChangeTag)
               }
           }
         }
@@ -75,7 +76,11 @@
       else { return }
 
       state.withState {
-        $0.changeTag = modifications.compactMap(\._recordChangeTag).max() ?? $0.changeTag
+        for changeTag in modifications.compactMap(\._recordChangeTag) {
+          if changeTag.isNewerChangeTag(than: $0.currentChangeTag) {
+            $0.currentChangeTag = changeTag
+          }
+        }
       }
 
       await parentSyncEngine.handleEvent(
@@ -134,7 +139,7 @@
   @available(iOS 17, macOS 14, tvOS 17, watchOS 10, *)
   package final class MockSyncEngineState: CKSyncEngineStateProtocol {
     package struct State: Sendable {
-      package var changeTag = 0
+      package var currentChangeTag: String?
       package var hasPendingUntrackedChanges = false
       package var pendingDatabaseChanges:
         OrderedDictionary<CKRecordZone.ID, CKSyncEngine.PendingDatabaseChange> = [:]
@@ -513,4 +518,11 @@
       }
     }
   }
+
+  extension String {
+    package func isNewerChangeTag(than other: String?) -> Bool {
+      guard let other else { return true }
+      return self.count != other.count ? self.count > other.count : self > other
+    }
+  }
 #endif

Tests/SQLiteDataTests/CloudKitTests/CloudKitTests.swift

@@ -888,7 +888,7 @@
         let record = try syncEngine.private.database.record(for: RemindersList.recordID(for: 1))
         record.setValue("Work", forKey: "title", at: now)
         // NB: Manually setting '_recordChangeTag' simulates another device saving a record.
-        record._recordChangeTag = .random(in: 9999 ... .max)
+        record._recordChangeTag = "zz"
         try await syncEngine.modifyRecords(scope: .private, saving: [record]).notify()
 
         assertQuery(Reminder.all, database: userDatabase.database) {

Tests/SQLiteDataTests/CloudKitTests/MockSyncEngineTests.swift

@@ -76,6 +76,24 @@
         try await syncEngine.processPendingRecordZoneChanges(scope: .private)
         #expect(!syncEngine.private.state.hasPendingUntrackedChanges)
       }
+
+      @Test func isNewerChangeTag() {
+        #expect("0".isNewerChangeTag(than: nil))
+
+        #expect(!"0".isNewerChangeTag(than: "0"))
+        #expect(!"z".isNewerChangeTag(than: "z"))
+
+        #expect("1".isNewerChangeTag(than: "0"))
+        #expect(!"0".isNewerChangeTag(than: "1"))
+        #expect("a".isNewerChangeTag(than: "9"))
+        #expect(!"9".isNewerChangeTag(than: "a"))
+        #expect("z".isNewerChangeTag(than: "a"))
+
+        #expect("10".isNewerChangeTag(than: "z"))
+        #expect(!"z".isNewerChangeTag(than: "10"))
+        #expect("100".isNewerChangeTag(than: "zz"))
+        #expect(!"zz".isNewerChangeTag(than: "100"))
+      }
     }
   }
 #endif

Tests/SQLiteDataTests/CloudKitTests/NextRecordZoneChangeBatchTests.swift

@@ -312,7 +312,7 @@
                       recordType: "remindersLists",
                       parent: nil,
                       share: nil,
-                      recordChangeTag: 3,
+                      recordChangeTag: "2",
                       id: 1,
                       id🗓️: 0,
                       title: "Personal 3",