SwiftUI Previews crashing with prepareDependencies

[OddMagnet]

I'm currently working through the documentation to add CloudKit Sync

Specifically I'm at the part where it shows how to use SQLite Data in Previews

#Preview {
    try! prepareDependencies {
        try! $0.bootstrapDatabase()
    }
    // ...
}

My preview looks pretty much exactly the same, I've also tried using let _ = so I wouldn't need the return before my view

#Preview {
    try! prepareDependencies {
        try! $0.bootstrapDatabase()
    }
    return ContentView()
}

For the bootstrapDatabase function my code is also very similar to what the docs show:

extension DependencyValues {
    mutating func bootstrapDatabase() throws {
        defaultDatabase = try appDatabase()
        defaultSyncEngine = try SyncEngine(
            for: defaultDatabase,
            tables: Issue.self, Tag.self, IssueTag.self
        )
    }

    // MARK: - Private

    // MARK: Logger

    private var dbLogger: Logger { Logger(subsystem: "MyApp", category: "Database") }

    // MARK: App Database

    func appDatabase() throws -> any DatabaseWriter {
        @Dependency(\.context) var context

        // MARK: - Database Configuration
        var configuration = Configuration()
        configuration.foreignKeysEnabled = true
        #if DEBUG
            configuration.prepareDatabase { db in
                try db.attachMetadatabase()
                db.trace(options: .profile) { traceEvent in
                    if context == .preview {
                        print("\(traceEvent.expandedDescription)")
                    } else {
                        dbLogger.debug("\(traceEvent.expandedDescription)")
                    }
                }
            }
        #endif

        // MARK: - Database Creation
        let database: any DatabaseWriter
        if context == .preview {
            database = try DatabaseQueue(configuration: configuration)
        } else {
            let path = context == .live
            ? URL.documentsDirectory.appending(component: "db.sqlite").path()
            : URL.temporaryDirectory.appending(component: "\(UUID().uuidString)-db.sqlite").path()
            dbLogger.info("open \(path)")
            database = try DatabasePool(path: path, configuration: configuration)
        }

        // MARK: - Database Migrations / Creation
        var migrator = DatabaseMigrator()
        #if DEBUG
            migrator.eraseDatabaseOnSchemaChange = true
        #endif
        migrator.registerMigration("Create tables") { try createTables(in: $0) }
        try migrator.migrate(database)

        return database
    }

    // MARK: Migrations

    private func createTables(in db: Database) throws { /* ... */ }
}

I've added a do { ... } catch { ... } and the error I'm getting is InvalidDatabasePath()

[OddMagnet]

Like so often, I discover what's causing the problem right after posting a discussion, even though I spent an hour trying things while writing the discussion post 🙄

I needed to make this change in bootstrapDatabase()

    mutating func bootstrapDatabase() throws {
        defaultDatabase = try appDatabase()
        if context != .preview { // <-- exclude SyncEngine from previews
            defaultSyncEngine = try SyncEngine(
                for: defaultDatabase,
                tables: Issue.self, Tag.self, IssueTag.self
            )
        }
    }

and this one in appDatabase()

    private func appDatabase() throws -> any DatabaseWriter {
        /* ... */

        // MARK: - Database Configuration
        var configuration = Configuration()
        configuration.foreignKeysEnabled = true
        #if DEBUG
            configuration.prepareDatabase { db in
                if context != .preview { <-- don't attach metadatabase for previews
                    try db.attachMetadatabase()
                }
                /* ... */
            }
        #endif

        /* ... */

        return database
    }