Ensure access to PDFDocument is always concurrency safe

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.9
+// swift-tools-version:6.0
 
 //
 // This source file is part of the Stanford Spezi open-source project
@@ -12,13 +12,6 @@ import class Foundation.ProcessInfo
 import PackageDescription
 
 
-#if swift(<6)
-let swiftConcurrency: SwiftSetting = .enableExperimentalFeature("StrictConcurrency")
-#else
-let swiftConcurrency: SwiftSetting = .enableUpcomingFeature("StrictConcurrency")
-#endif
-
-
 let package = Package(
     name: "SpeziOnboarding",
     defaultLocalization: "en",
@@ -47,7 +40,6 @@ let package = Package(
                 .product(name: "TPPDF", package: "TPPDF")
             ],
             swiftSettings: [
-                swiftConcurrency,
                 .enableUpcomingFeature("ExistentialAny")
             ],
             plugins: [] + swiftLintPlugin()
@@ -61,7 +53,6 @@ let package = Package(
                 .process("Resources/")
             ],
             swiftSettings: [
-                swiftConcurrency,
                 .enableUpcomingFeature("ExistentialAny")
             ],
             plugins: [] + swiftLintPlugin()

Sources/SpeziOnboarding/ConsentConstraint.swift

@@ -17,5 +17,5 @@ public protocol ConsentConstraint: Standard {
     /// 
     /// - Parameters:
     ///     - consent: The exported consent form represented as `ConsentDocumentExport` that should be added.            
-    func store(consent: ConsentDocumentExport) async throws
+    func store(consent: consuming sending ConsentDocumentExport) async throws
 }

Sources/SpeziOnboarding/ConsentView/ConsentDocument+ExportConfiguration.swift

@@ -69,23 +69,23 @@ extension ConsentDocument {
             ///   - headerTitleFont: The font used for the header title.
             ///   - headerExportTimeStampFont: The font used for the header timestamp.
             public init(
-                    signatureNameFont: UIFont,
-                    signaturePrefixFont: UIFont,
-                    documentContentFont: UIFont,
-                    headerTitleFont: UIFont,
-                    headerExportTimeStampFont: UIFont
-                ) {
-                    self.signatureNameFont = signatureNameFont
-                    self.signaturePrefixFont = signaturePrefixFont
-                    self.documentContentFont = documentContentFont
-                    self.headerTitleFont = headerTitleFont
-                    self.headerExportTimeStampFont = headerExportTimeStampFont
-                }
+                signatureNameFont: UIFont,
+                signaturePrefixFont: UIFont,
+                documentContentFont: UIFont,
+                headerTitleFont: UIFont,
+                headerExportTimeStampFont: UIFont
+            ) {
+                self.signatureNameFont = signatureNameFont
+                self.signaturePrefixFont = signaturePrefixFont
+                self.documentContentFont = documentContentFont
+                self.headerTitleFont = headerTitleFont
+                self.headerExportTimeStampFont = headerExportTimeStampFont
+            }
         }
         #else
         /// The ``FontSettings`` store configuration of the fonts used to render the exported
         /// consent document, i.e., fonts for the content, title and signature.
-        public struct FontSettings {
+        public struct FontSettings: @unchecked Sendable {
             /// The font of the name rendered below the signature line.
             public let signatureNameFont: NSFont
             /// The font of the prefix of the signature ("X" in most cases).
@@ -107,18 +107,18 @@ extension ConsentDocument {
             ///   - headerTitleFont: The font used for the header title.
             ///   - headerExportTimeStampFont: The font used for the header timestamp.
             public init(
-                    signatureNameFont: NSFont,
-                    signaturePrefixFont: NSFont,
-                    documentContentFont: NSFont,
-                    headerTitleFont: NSFont,
-                    headerExportTimeStampFont: NSFont
-                ) {
-                    self.signatureNameFont = signatureNameFont
-                    self.signaturePrefixFont = signaturePrefixFont
-                    self.documentContentFont = documentContentFont
-                    self.headerTitleFont = headerTitleFont
-                    self.headerExportTimeStampFont = headerExportTimeStampFont
-                }
+                signatureNameFont: NSFont,
+                signaturePrefixFont: NSFont,
+                documentContentFont: NSFont,
+                headerTitleFont: NSFont,
+                headerExportTimeStampFont: NSFont
+            ) {
+                self.signatureNameFont = signatureNameFont
+                self.signaturePrefixFont = signaturePrefixFont
+                self.documentContentFont = documentContentFont
+                self.headerTitleFont = headerTitleFont
+                self.headerExportTimeStampFont = headerExportTimeStampFont
+            }
         }
         #endif
 
@@ -127,7 +127,7 @@ extension ConsentDocument {
         let paperSize: PaperSize
         let includingTimestamp: Bool
         let fontSettings: FontSettings
-        
+
 
         /// Creates an `ExportConfiguration` specifying the properties of the exported consent form.
         /// - Parameters:

Sources/SpeziOnboarding/ConsentView/ConsentDocument.swift

@@ -47,7 +47,7 @@
     private let familyNamePlaceholder: LocalizedStringResource
 
     let documentExport: ConsentDocumentExport
-    
+
     @Environment(\.colorScheme) var colorScheme
     @State var name = PersonNameComponents()
     #if !os(macOS)
@@ -66,7 +66,7 @@
                 #if !os(macOS)
                 nameInputView
                 #else
-                // Need to wrap the `NameFieldRow` from SpeziViews into a SwiftUI `Form, otherwise the Label is omitted
+                // Need to wrap the `NameFieldRow` from SpeziViews into a SwiftUI `Form`, otherwise the Label is omitted
                 Form {
                     nameInputView
                 }

Sources/SpeziOnboarding/ConsentView/ConsentDocumentExport+Export.swift

@@ -11,6 +11,7 @@
 import SwiftUI
 import TPPDF
 
+
 /// Extension of `ConsentDocumentExport` enabling the export of the signed consent page.
 extension ConsentDocumentExport {
     /// Generates a `PDFAttributedText` containing the timestamp of the time at which the PDF was exported.
@@ -57,7 +58,7 @@
             options: .init(interpretedSyntax: .inlineOnlyPreservingWhitespace)
         )) ?? AttributedString(String(localized: "MARKDOWN_LOADING_ERROR", bundle: .module))
 
         markdownString.font = exportConfiguration.fontSettings.documentContentFont
 
         return PDFAttributedText(text: NSAttributedString(markdownString))
     }

Sources/SpeziOnboarding/ConsentView/ConsentDocumentExport.swift

@@ -10,12 +10,13 @@
 import PencilKit
 import SwiftUI
 
+
 /// A type representing an exported `ConsentDocument`. It holds the exported `PDFDocument` and the corresponding document identifier String.
-@Observable
-public final class ConsentDocumentExport: Equatable, Sendable {
+public final class ConsentDocumentExport: Equatable {
     /// Provides default values for fields related to the `ConsentDocumentExport`.
     public enum Defaults {
         /// Default value for a document identifier.
+        /// 
         /// This identifier will be used as default value if no identifier is provided.
         public static let documentIdentifier = "ConsentDocument"
     }
@@ -25,9 +26,10 @@ public final class ConsentDocumentExport: Equatable, Sendable {
     var cachedPDF: PDFDocument?
 
     /// An unique identifier for the exported `ConsentDocument`.
+    ///
     /// Corresponds to the identifier which was passed  when creating the `ConsentDocument` using an `OnboardingConsentView`.
     public let documentIdentifier: String
-    
+
     /// The name of the person which signed the document.
     public var name = PersonNameComponents()
     #if !os(macOS)
@@ -40,48 +42,48 @@ public final class ConsentDocumentExport: Equatable, Sendable {
     public var signature = String()
     #endif
 
-    /// The `PDFDocument` exported from a `ConsentDocument`.
-    /// This property is asynchronous and accesing it potentially triggers the export of the PDF from the underlying `ConsentDocument`,
-    /// if the `ConsentDocument` has not been previously exported or the `PDFDocument` was not cached.
-    /// For now, we always require a PDF to be cached to create a ConsentDocumentExport. In the future, we might change this to lazy-PDF loading.
-    @MainActor public var pdf: PDFDocument {
-        get async {
-            if let pdf = cachedPDF {
-                return pdf
-            }
-
-            guard let pdf = try? await export() else {
-                return .init()
-            }
-
-            cachedPDF = pdf
-            return pdf
-        }
-    }
-
-
+
     /// Creates a `ConsentDocumentExport`, which holds an exported PDF and the corresponding document identifier string.
     /// - Parameters:
     ///   - markdown: The markdown text for the document, which is shown to the user.
-    ///   - documentIdentfier: A unique String identifying the exported `ConsentDocument`.
     ///   - exportConfiguration: The `ExportConfiguration` holding the properties of the document.
+    ///   - documentIdentifier: A unique String identifying the exported `ConsentDocument`.
     ///   - cachedPDF: A `PDFDocument` exported from a `ConsentDocument`.
     init(
         markdown: @escaping () async -> Data,
         exportConfiguration: ConsentDocument.ExportConfiguration,
         documentIdentifier: String,
-        cachedPDF: PDFDocument? = nil
+        cachedPDF: sending PDFDocument? = nil
     ) {
         self.asyncMarkdown = markdown
         self.exportConfiguration = exportConfiguration
         self.documentIdentifier = documentIdentifier
         self.cachedPDF = cachedPDF
     }
-
+
+
     public static func == (lhs: ConsentDocumentExport, rhs: ConsentDocumentExport) -> Bool {
         lhs.documentIdentifier == rhs.documentIdentifier &&
         lhs.name == rhs.name &&
         lhs.signature == rhs.signature &&
         lhs.cachedPDF == rhs.cachedPDF
     }
+
+
+    /// Consume the exported `PDFDocument` from a `ConsentDocument`.
+    ///
+    /// This method consumes the `ConsentDocumentExport/cachedPDF` by retrieving the exported `PDFDocument`.
+    ///
+    /// - Note: For now, we always require a PDF to be cached to create a `ConsentDocumentExport`. In the future, we might change this to lazy-PDF loading.
+    public consuming func consumePDF() -> sending PDFDocument {
+        // Accessing `cachedPDF` via `take()` ensures single consumption of the `PDFDocument` by transferring ownership
+        // from the enclosing class and leaving `nil` behind after the access. Though `ConsentDocumentExport` is a reference
+        // type, this manual ownership model guarantees the PDF is only used once, enabling safe cross-concurrency transfer.
+        // The explicit `sending` return type reinforces transfer semantics, while `take()` enforces single-access at runtime.
+        // This pattern provides compiler-verifiable safety for the `PDFDocument` transfer despite the class's reference semantics.
+        //
+        // See similar discussion: https://forums.swift.org/t/swift-6-consume-optional-noncopyable-property-and-transfer-sending-it-out/72414/3
+        nonisolated(unsafe) let cachedPDF = cachedPDF.take() ?? .init()
+        return cachedPDF
+    }
 }

Sources/SpeziOnboarding/ConsentView/ExportConfiguration+Defaults.swift

@@ -9,55 +9,56 @@
 import Foundation
 import SwiftUI
 
+
 extension ConsentDocument.ExportConfiguration {
     /// Provides default values for fields related to the `ConsentDocumentExportConfiguration`.
     public enum Defaults {
-       #if !os(macOS)
-       /// Default export font settings with fixed font sizes, ensuring a consistent appearance across platforms.
-       ///
-       /// This configuration uses `systemFont` and `boldSystemFont` with absolute font sizes to achieve uniform font sizes
-       /// on different operating systems such as macOS, iOS, and visionOS.
-       public static let defaultExportFontSettings = FontSettings(
-           signatureNameFont: UIFont.systemFont(ofSize: 10),
-           signaturePrefixFont: UIFont.boldSystemFont(ofSize: 12),
-           documentContentFont: UIFont.systemFont(ofSize: 12),
-           headerTitleFont: UIFont.boldSystemFont(ofSize: 28),
-           headerExportTimeStampFont: UIFont.systemFont(ofSize: 8)
-       )
-       
-       /// Default font based on system standards. In contrast to defaultExportFontSettings,
-       /// the font sizes might change according to the system settings, potentially leading to varying exported PDF documents
-       /// on devices with different system settings (e.g., larger default font size).
-       public static let defaultSystemDefaultFontSettings = FontSettings(
-           signatureNameFont: UIFont.preferredFont(forTextStyle: .subheadline),
-           signaturePrefixFont: UIFont.preferredFont(forTextStyle: .title2),
-           documentContentFont: UIFont.preferredFont(forTextStyle: .body),
-           headerTitleFont: UIFont.boldSystemFont(ofSize: UIFont.preferredFont(forTextStyle: .largeTitle).pointSize),
-           headerExportTimeStampFont: UIFont.preferredFont(forTextStyle: .caption1)
-       )
-       #else
-       /// Default export font settings with fixed font sizes, ensuring a consistent appearance across platforms.
-       ///
-       /// This configuration uses `systemFont` and `boldSystemFont` with absolute font sizes to achieve uniform font sizes
-       /// on different operating systems such as macOS, iOS, and visionOS.
-       public static let defaultExportFontSettings = FontSettings(
-           signatureNameFont: NSFont.systemFont(ofSize: 10),
-           signaturePrefixFont: NSFont.boldSystemFont(ofSize: 12),
-           documentContentFont: NSFont.systemFont(ofSize: 12),
-           headerTitleFont: NSFont.boldSystemFont(ofSize: 28),
-           headerExportTimeStampFont: NSFont.systemFont(ofSize: 8)
-       )
-       
-       /// Default font based on system standards. In contrast to defaultExportFontSettings,
-       /// the font sizes might change according to the system settings, potentially leading to varying exported PDF documents
-       /// on devices with different system settings (e.g., larger default font size).
-       public static let defaultSystemDefaultFontSettings = FontSettings(
-           signatureNameFont: NSFont.preferredFont(forTextStyle: .subheadline),
-           signaturePrefixFont: NSFont.preferredFont(forTextStyle: .title2),
-           documentContentFont: NSFont.preferredFont(forTextStyle: .body),
-           headerTitleFont: NSFont.boldSystemFont(ofSize: NSFont.preferredFont(forTextStyle: .largeTitle).pointSize),
-           headerExportTimeStampFont: NSFont.preferredFont(forTextStyle: .caption1)
-       )
-       #endif
-   }
+        #if !os(macOS)
+        /// Default export font settings with fixed font sizes, ensuring a consistent appearance across platforms.
+        ///
+        /// This configuration uses `systemFont` and `boldSystemFont` with absolute font sizes to achieve uniform font sizes
+        /// on different operating systems such as macOS, iOS, and visionOS.
+        public static let defaultExportFontSettings = FontSettings(
+            signatureNameFont: UIFont.systemFont(ofSize: 10),
+            signaturePrefixFont: UIFont.boldSystemFont(ofSize: 12),
+            documentContentFont: UIFont.systemFont(ofSize: 12),
+            headerTitleFont: UIFont.boldSystemFont(ofSize: 28),
+            headerExportTimeStampFont: UIFont.systemFont(ofSize: 8)
+        )
+
+        /// Default font based on system standards. In contrast to defaultExportFontSettings,
+        /// the font sizes might change according to the system settings, potentially leading to varying exported PDF documents
+        /// on devices with different system settings (e.g., larger default font size).
+        public static let defaultSystemDefaultFontSettings = FontSettings(
+            signatureNameFont: UIFont.preferredFont(forTextStyle: .subheadline),
+            signaturePrefixFont: UIFont.preferredFont(forTextStyle: .title2),
+            documentContentFont: UIFont.preferredFont(forTextStyle: .body),
+            headerTitleFont: UIFont.boldSystemFont(ofSize: UIFont.preferredFont(forTextStyle: .largeTitle).pointSize),
+            headerExportTimeStampFont: UIFont.preferredFont(forTextStyle: .caption1)
+        )
+        #else
+        /// Default export font settings with fixed font sizes, ensuring a consistent appearance across platforms.
+        ///
+        /// This configuration uses `systemFont` and `boldSystemFont` with absolute font sizes to achieve uniform font sizes
+        /// on different operating systems such as macOS, iOS, and visionOS.
+        public static let defaultExportFontSettings = FontSettings(
+            signatureNameFont: NSFont.systemFont(ofSize: 10),
+            signaturePrefixFont: NSFont.boldSystemFont(ofSize: 12),
+            documentContentFont: NSFont.systemFont(ofSize: 12),
+            headerTitleFont: NSFont.boldSystemFont(ofSize: 28),
+            headerExportTimeStampFont: NSFont.systemFont(ofSize: 8)
+        )
+
+        /// Default font based on system standards. In contrast to defaultExportFontSettings,
+        /// the font sizes might change according to the system settings, potentially leading to varying exported PDF documents
+        /// on devices with different system settings (e.g., larger default font size).
+        public static let defaultSystemDefaultFontSettings = FontSettings(
+            signatureNameFont: NSFont.preferredFont(forTextStyle: .subheadline),
+            signaturePrefixFont: NSFont.preferredFont(forTextStyle: .title2),
+            documentContentFont: NSFont.preferredFont(forTextStyle: .body),
+            headerTitleFont: NSFont.boldSystemFont(ofSize: NSFont.preferredFont(forTextStyle: .largeTitle).pointSize),
+            headerExportTimeStampFont: NSFont.preferredFont(forTextStyle: .caption1)
+        )
+        #endif
+    }
 }

Sources/SpeziOnboarding/ConsentView/OnboardingConsentView+ShareSheet.swift

@@ -46,6 +46,7 @@ extension OnboardingConsentView {
         let sharedItem: PDFDocument
 
 
+        @MainActor
         func show() {
             // Note: Need to write down the PDF to storage as in-memory PDFs are not recognized properly
             let temporaryPath = FileManager.default.temporaryDirectory.appendingPathComponent(

Sources/SpeziOnboarding/OnboardingConstraint.swift

@@ -33,5 +33,5 @@ public protocol OnboardingConstraint: Standard {
         Please use `ConsentConstraint.store(consent: PDFDocument, identifier: String)` instead.
         """
     )
-    func store(consent: PDFDocument) async
+    func store(consent: sending PDFDocument) async
 }