Move Swift source code into KMP libraries via SKIE Bundling. (#1655)

This change relocates all Swift source code directly into the
respective Kotlin modules, leveraging SKIE's [Swift Code Bundling](https://skie.touchlab.co/features/swift-code-bundling)
feature. This allows us to distribute the logic within a single
framework.

Having the code in a single framework enables downstream projects to
build their own "umbrella" XCFramework that encapsulates both their
custom Kotlin code and the Multipaz core.

Crucially, this prevents the Framework Boundary (or "Diamond Dependency")
problem caused by Kotlin/Native's closed-world compilation model. If a
downstream iOS app previously depended on a standalone Multipaz SPM
package while also using a local KMP shared module that depended on
Multipaz, Xcode would generate two isolated Kotlin runtimes. This
resulted in fatal type mismatches across the Objective-C headers, where
types from the local module (e.g., `Shared.Document`) were entirely
incompatible with types from the SPM package (e.g., `Multipaz.Document`).

By allowing downstream projects to compile a single umbrella framework,
SKIE extracts and compiles our Swift extensions against that unified
header, ensuring perfect type resolution and a single runtime.

Test: Manually tested TestApp, Swift TestApp, and 3rd party consumer.

Signed-off-by: David Zeuthen <zeuthen@google.com>

Author: davidz25

Package.swift

@@ -7,18 +7,9 @@ let package = Package(
     .iOS(.v26),
    ],
    products: [
-      .library(name: "Multipaz", targets: ["MultipazSwift"]),
-      .library(name: "MultipazCore", targets: ["Multipaz"])
+      .library(name: "Multipaz", targets: ["Multipaz"]),
    ],
    targets: [
-        .target(
-            name: "MultipazSwift",
-            dependencies: ["Multipaz"],
-            path: "multipaz-swift/Sources/MultipazSwift",
-            resources: [
-                .process("Resources/default_card_art.png")
-            ]
-        ),
         .binaryTarget(
             name: "Multipaz",
             path: "xcframework/build/XCFrameworks/release/Multipaz.xcframework"

README.md

@@ -26,8 +26,8 @@ The project provides libraries written in [Kotlin Multiplatform](https://kotlinl
 - `multipaz-longfellow` bundles the [Google Longfellow-ZK](https://github.com/google/longfellow-zk) library
   and integrates with the core `multipaz` for Zero-Knowledge Proofs
   according to latest available [ISO/IEC 18013-5 Second Edition draft](https://github.com/ISOWG10/ISO-18013).
-- `multipaz-swift` contains Swift and [SwiftUI](https://developer.apple.com/swiftui/)
-  functionality to easier use Multipaz in Swift applications on iOS.
+- `multipaz-swiftui` contains SwiftUI components which can be used in
+  Swift applications.
 
 ## Command-line tool
 
@@ -62,16 +62,9 @@ late 2026 or early 2027.
 
 We are also making Multipaz available as a [Swift package](https://github.com/openwallet-foundation/multipaz/blob/main/Package.swift)
 which includes an the `multipaz`, `multipaz-doctypes`, `multipaz-doctypes`,
-`multipaz-longfellow`, and `multipaz-swift` libraries. This is built using
-[SKIE](https://skie.touchlab.co/). Be careful relying on this as Swift/Kotlin
-interop technology might change in the near future.
-
-The Swift package exposes two products:
-
-- `Multipaz` includes the higher-level `multipaz-swift` wrapper APIs.
-- `MultipazCore` exposes the core binary target directly for applications that
-  build their own UI and only need the lower-level APIs. When using this
-  product, the module import remains `import Multipaz`.
+`multipaz-longfellow`, and `multipaz-swiftui` libraries. This is built using
+[SKIE](https://skie.touchlab.co/). Be careful relying on this as Swift/Kotlin interop technology
+might change in the near future with e.g. [Swift Export](https://kotlinlang.org/docs/native-swift-export.html).
 
 At this point both API interfaces and data stored on disk is subject to change
 but we expect to provide stability guarantees post 1.0. We only expect minor changes
@@ -100,12 +93,16 @@ developers and as such has a lot of options and settings. It's intended to
 exercise all code in the libraries. Prebuilt APKs are available from
 https://apps.multipaz.org.
 
+For a SwiftUI version of `samples/testapp` see `samples/SwiftTestApp` which works
+on iOS and is a testbed for the Swift bindings as well as the SwiftUI components
+in `multipaz-swiftui`.
+
 For a fully-featured proximity reader app using Multipaz, see
 [MpzIdentityReader](https://github.com/openwallet-foundation/multipaz-identity-reader/).
 Prebuilt APKs are available from https://apps.multipaz.org.
 
 For an over-the-Internet verifier supporting OpenID4VP (both W3C DC API and
-URI schemes) and ISO/IEC 18013-7 Annex C see https://verifier.multipaz.org.
+URI schemes) and ISO/IEC 18013-7 Annex A and C see https://verifier.multipaz.org.
 
 To see how to use the Multipaz in a 3rd party project, see
 https://github.com/openwallet-foundation/multipaz-samples/ which includes

multipaz-swift/Sources/MultipazSwift/DocumentExt.swift

@@ -0,0 +1,134 @@
+@file:OptIn(ExperimentalWasmDsl::class)
+
+import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
+plugins {
+    alias(libs.plugins.kotlinMultiplatform)
+    alias(libs.plugins.skie)
+    id("maven-publish")
+    id("org.jetbrains.dokka") version "2.1.0"
+}
+
+val projectVersionCode: Int by rootProject.extra
+val projectVersionName: String by rootProject.extra
+
+val disableWebTargets = project.properties["disable.web.targets"]?.toString()?.toBoolean() ?: false
+
+kotlin {
+    jvmToolchain(17)
+
+    compilerOptions {
+        optIn.add("kotlin.time.ExperimentalTime")
+    }
+
+    jvm()
+
+    if (!disableWebTargets) {
+        js {
+            outputModuleName = "multipaz-swiftui"
+            browser {
+            }
+            binaries.executable()
+        }
+
+        wasmJs {
+            outputModuleName = "multipaz-swiftui"
+            browser {
+            }
+            binaries.executable()
+        }
+    }
+
+    listOf(
+        iosX64(),
+        iosArm64(),
+        iosSimulatorArm64()
+    ).forEach {
+        val platform = when (it.name) {
+            "iosX64" -> "iphonesimulator"
+            "iosArm64" -> "iphoneos"
+            "iosSimulatorArm64" -> "iphonesimulator"
+            else -> error("Unsupported target ${it.name}")
+        }
+        it.binaries.all {
+            linkerOpts(
+                "-L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/${platform}/",
+                "-Wl,-rpath,/usr/lib/swift"
+            )
+        }
+    }
+
+    sourceSets {
+        val commonMain by getting {
+            dependencies {
+                implementation(project(":multipaz"))
+                implementation(libs.kotlinx.datetime)
+                implementation(libs.kotlinx.io.bytestring)
+                implementation(libs.kotlinx.serialization.json)
+                api(project(":multipaz"))
+            }
+        }
+
+        val commonTest by getting {
+            dependencies {
+                implementation(libs.kotlin.test)
+                implementation(libs.kotlinx.coroutines.test)
+            }
+        }
+
+        val jvmMain by getting {
+            dependencies {
+            }
+        }
+
+        val jvmTest by getting {
+            dependencies {
+            }
+        }
+
+        if (!disableWebTargets) {
+            val jsTest by getting {
+                dependencies {
+                    implementation(libs.kotlin.wrappers.web)
+                }
+            }
+        }
+    }
+}
+
+group = "org.multipaz"
+version = projectVersionName
+
+publishing {
+    repositories {
+        maven {
+            url = uri(rootProject.layout.buildDirectory.dir("staging-repo"))
+        }
+    }
+    publications.withType(MavenPublication::class) {
+        pom {
+            name.set("multipaz-swiftui")
+            description.set("Multipaz SDK SwiftUI module")
+            url.set("https://github.com/openwallet-foundation/multipaz")
+            licenses {
+                license {
+                    name.set("Apache-2.0")
+                    url.set("https://opensource.org/licenses/Apache-2.0")
+                    distribution.set("repo")
+                }
+            }
+            developers {
+                developer {
+                    id.set("zeuthen")
+                    name.set("David Zeuthen")
+                    email.set("zeuthen@google.com")
+                }
+            }
+            scm {
+                connection.set("scm:git:git://github.com/openwallet-foundation/multipaz.git")
+                developerConnection.set("scm:git:ssh://github.com/openwallet-foundation/multipaz.git")
+                url.set("https://github.com/openwallet-foundation/multipaz")
+            }
+        }
+    }
+}
+

multipaz-swift/Sources/MultipazSwift/Resources/default_card_art.png

@@ -1,4 +1,3 @@
-import Multipaz
 import SwiftUI
 
 func getIconName(claim: Claim) -> String {

multipaz-swiftui/build.gradle.kts

@@ -1,5 +1,4 @@
 import SwiftUI
-@preconcurrency import Multipaz
 
 private struct ConsentPromptDialogData: Identifiable, Equatable {
     let id = UUID()