SwiftUI.View image snapshot size doesn't use preference values

[CraigSiemens]

Describe the bug

When taking an image snapshot of a SwiftUI View that uses a preference to affect it's size, the resulting image will:

• be sized without the preference value
• be drawn using the preference value

This causes the view to either:

• be smaller than the image, so there's extra padding
• be larger than the image, causing content of the view to be cut off

To Reproduce

Take a snapshot of this ExampleView as .image(layout: .sizeThatFits)

struct ExampleView: View {
    @State private var size: CGSize = .init(width: 20, height: 20)
    
    var body: some View {
        Color.red
            .preference(key: SizePreferenceKey.self, value: CGSize(width: 10, height: 10))
            .frame(width: size.width, height: size.height)
            .onPreferenceChange(SizePreferenceKey.self) { newSize in
                size = newSize
            }
            .border(.black)
    }
}

struct SizePreferenceKey: PreferenceKey {
    typealias Value = CGSize
    
    static var defaultValue: Value = .init(width: 30, height: 30)
    
    static func reduce(value: inout Value, nextValue: () -> Value) {
        value
    }
}

Expected behavior
The image should be 10pt x 10pt matching the size of the red view with a black border.

Screenshots

The image is actually being created at 20pt x 20pt so there's extra space added around the view.

If the preference was set to a larger value (ie 50x50), the red view would be larger than the image causing the border to no longer be in the image.

Environment

• swift-snapshot-testing version 1.17.5
• Xcode 16.0
• Swift 6.0
• OS: iOS 18