Fix previews for CloudKit-enabled apps (#366)

* wip

* wip

* wip

* wip

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* Conditionally wrap CountersListView in NavigationStack

Author: stephencelis

Examples/CloudKitDemo/CloudKitDemoApp.swift

@@ -5,17 +5,22 @@ import SwiftUI
 @main
 struct CloudKitDemoApp: App {
   @UIApplicationDelegateAdaptor private var appDelegate: AppDelegate
+  @Dependency(\.context) var context
 
   init() {
-    try! prepareDependencies {
-      try $0.bootstrapDatabase()
+    if context == .live {
+      try! prepareDependencies {
+        try $0.bootstrapDatabase()
+      }
     }
   }
 
   var body: some Scene {
     WindowGroup {
-      NavigationStack {
-        CountersListView()
+      if context == .live {
+        NavigationStack {
+          CountersListView()
+        }
       }
     }
   }

Examples/CloudKitDemo/CountersListFeature.swift

@@ -1,7 +1,6 @@
 import CloudKit
 import SQLiteData
 import SwiftUI
-import SwiftUINavigation
 
 struct CountersListView: View {
   @FetchAll var counters: [Counter]
@@ -107,3 +106,12 @@ struct CounterRow: View {
     }
   }
 }
+
+#Preview {
+  let _ = try! prepareDependencies {
+    try $0.bootstrapDatabase()
+  }
+  NavigationStack {
+    CountersListView()
+  }
+}

Examples/CloudKitDemo/Schema.swift

@@ -10,8 +10,11 @@ nonisolated struct Counter: Identifiable {
 
 extension DependencyValues {
   mutating func bootstrapDatabase() throws {
-    @Dependency(\.context) var context
-    let database = try SQLiteData.defaultDatabase()
+    var configuration = Configuration()
+    configuration.prepareDatabase { db in
+      try db.attachMetadatabase()
+    }
+    let database = try SQLiteData.defaultDatabase(configuration: configuration)
     logger.debug(
       """
       App database

Examples/Examples.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved

@@ -77,7 +77,6 @@ extension Int {
 
 extension DependencyValues {
   mutating func bootstrapDatabase() throws {
-    @Dependency(\.context) var context
     let database = try SQLiteData.defaultDatabase()
     logger.debug(
       """

Examples/SyncUps/Schema.swift

@@ -99,10 +99,11 @@
       repeat (each T2).PrimaryKey.QueryOutput: IdentifierStringConvertible,
       repeat (each T2).TableColumns.PrimaryColumn: WritableTableColumnExpression
     {
+      @Dependency(\.context) var context
       let containerIdentifier =
         containerIdentifier
         ?? ModelConfiguration(groupContainer: .automatic).cloudKitContainerIdentifier
-
+        ?? (context == .preview ? "preview" : nil)
       var allTables: [any SynchronizableTable] = []
       var allPrivateTables: [any SynchronizableTable] = []
       for table in repeat each tables {
@@ -113,7 +114,6 @@
       }
       let userDatabase = UserDatabase(database: database)
 
-      @Dependency(\.context) var context
       guard context == .live
       else {
         let privateDatabase = MockCloudDatabase(databaseScope: .private)
@@ -325,7 +325,10 @@
           : URL(filePath: metadatabase.path).lastPathComponent
         let attachedMetadatabaseName =
           URL(string: attachedMetadatabasePath)?.lastPathComponent ?? ""
-        if metadatabaseName != attachedMetadatabaseName {
+        @Dependency(\.context) var context
+        if metadatabaseName != attachedMetadatabaseName
+          && !(context == .preview && attachedMetadatabaseName.isEmpty)
+        {
           throw SchemaError(
             reason: .metadatabaseMismatch(
               attachedPath: attachedMetadatabasePath,
@@ -337,7 +340,6 @@
               """
           )
         }
-
       } else {
         try #sql(
           """
@@ -2151,9 +2153,11 @@
     /// - Parameter containerIdentifier: The identifier of the CloudKit container used to
     /// synchronize data. Defaults to the value set in the app's entitlements.
     public func attachMetadatabase(containerIdentifier: String? = nil) throws {
+      @Dependency(\.context) var context
       let containerIdentifier =
         containerIdentifier
         ?? ModelConfiguration(groupContainer: .automatic).cloudKitContainerIdentifier
+        ?? (context == .preview ? "preview" : nil)
 
       guard let containerIdentifier else {
         throw SyncEngine.SchemaError.noCloudKitContainer