Swift: Detect code running in SwiftUI preview

ProcessInfo+SwiftUIPreview.swift

extension ProcessInfo {

    var isSwiftUIPreview: Bool {
        environment["XCODE_RUNNING_FOR_PREVIEWS"] == "1"
    }

    // or:

    static func isOnPreview() -> Bool {
        return processInfo.processName == "XCPreviewAgent"
    }
}