SwiftUI, SwiftData, WidgetKit - Missing 'previewContext' modifier

Question

Cannot Preview this file

Missing 'previewContext' modifier.

No bug anywhere else. Xcode 15, iOS 17

import SwiftUI
import WidgetKit
import SwiftData

struct DiemWidgetEntryView : View {
    var entry: DiemWidgetEntry

    // Used to work. I don't think it's the problem. 
    var body: some View {
        let diem: Diem = .init(from: entry.configuration.diem)
        
        DiemSharedView(diem: diem)
    }
}

#Preview {
    DiemWidgetEntryView(entry: DiemWidgetEntry(date: Date(), configuration: .christmas))
        .previewContext(WidgetPreviewContext(family: .systemSmall))
        .modelContainer(previewContainer)  // works everywhere else in my project
}

Answer 1

Copy everything out of the file, delete it, and recreate it.

I had the same issue, the preview-block worked when I copied it to a different location though. Recreating the file worked.