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Drive Swift cross-compilation and jniLibs staging from Gradle
The jextract task cross-compiles the package graph with the Swift Android SDK (--disable-sandbox so the swift-java callbacks sub-build can run Gradle), generated Java bindings and a patched SwiftKitCore source tree are added to the source set, and all required .so files are staged into jniLibs. The Unsigned annotation is replaced with an Android-compatible copy since the upstream source depends on jdk.jfr.
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2 files changed

Lines changed: 156 additions & 11 deletions

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‎Demo/app/build.gradle.kts‎

Lines changed: 120 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,111 @@ plugins {
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alias(libs.plugins.kotlin.compose)
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}
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// ---------------------------------------------------------------------------
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// swift-java (jextract, JNI mode) integration
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//
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// The Swift package graph (AndroidBluetooth + AndroidBluetoothBridge +
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// BluetoothDemoBridge) is cross-compiled to native `.so`s with the official
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// Swift Android SDK; the `JExtractSwiftPlugin` emits the Java JNI bindings as
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// a side effect of `swift build`. Gradle then adds the generated Java +
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// SwiftKitCore runtime sources to the source set and stages every required
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// `.so` into `jniLibs`.
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// ---------------------------------------------------------------------------
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val swiftPackageRoot: File = rootProject.projectDir
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val androidTriple = "aarch64-unknown-linux-android28"
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val swiftAbi = "arm64-v8a"
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val userHome: String = System.getProperty("user.home")
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// Configuration the Swift package is cross-compiled with, independent of the
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// Android build type. Override with `-PswiftBuildConfig=release`.
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val swiftBuildConfig: String = (findProperty("swiftBuildConfig") as String?) ?: "debug"
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// Locates both the toolchain and the matching Android SDK artifactbundle.
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val swiftToolchainVersion: String = (findProperty("swiftToolchainVersion") as String?) ?: "6.3.3"
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// The Android SDK's prebuilt Swift modules require the matching swift.org
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// toolchain. Override with `-PswiftBin=/path/to/swift` if installed elsewhere.
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val swiftBin: String = (findProperty("swiftBin") as String?)
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?: "$userHome/Library/Developer/Toolchains/swift-$swiftToolchainVersion-RELEASE.xctoolchain/usr/bin/swift"
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// swift-java's `enableJavaCallbacks` feature runs its own internal Gradle
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// sub-build to compile the generated Java callback interfaces, requiring a
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// modern JDK — independent of whatever JDK runs *this* Gradle build.
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// Override with `-PcallbacksJdkHome=/path/to/jdk`.
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val callbacksJdkHome: String = (findProperty("callbacksJdkHome") as String?)
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?: "/opt/homebrew/opt/openjdk@25"
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// SwiftPM plugin output convention: `outputs/<package-dir-lowercased>/<TargetName>/...`.
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// Both bridge targets generate Java: the AndroidBluetooth library's callback
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// bridge and the demo's UI-facing bridge.
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val generatedLibraryJavaDir = File(swiftPackageRoot, ".build/plugins/outputs/androidbluetooth/AndroidBluetoothBridge/destination/JExtractSwiftPlugin/src/generated/java")
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val generatedDemoJavaDir = File(swiftPackageRoot, ".build/plugins/outputs/demo/BluetoothDemoBridge/destination/JExtractSwiftPlugin/src/generated/java")
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val swiftKitCoreDir = File(swiftPackageRoot, ".build/checkouts/swift-java/SwiftKitCore/src/main/java")
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val swiftBuildDir = File(swiftPackageRoot, ".build/$androidTriple/$swiftBuildConfig")
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val swiftAndroidRuntimeDir = File(
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(findProperty("swiftAndroidRuntimeDir") as String?)
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?: "$userHome/Library/org.swift.swiftpm/swift-sdks/swift-${swiftToolchainVersion}-RELEASE_android.artifactbundle/swift-android/swift-resources/usr/lib/swift-aarch64/android"
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)
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// Supplies libc++_shared.so, which every Swift Android binary links against.
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val swiftAndroidSysroot = File(
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(findProperty("swiftAndroidSysroot") as String?)
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?: "$userHome/Library/org.swift.swiftpm/swift-sdks/swift-${swiftToolchainVersion}-RELEASE_android.artifactbundle/swift-android/ndk-sysroot"
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)
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// Cross-compile the Swift package + generate the JNI Java bindings.
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val jextract = tasks.register<Exec>("jextract") {
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workingDir = swiftPackageRoot
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environment("JAVA_HOME", callbacksJdkHome)
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commandLine(
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swiftBin, "build",
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"--swift-sdk", androidTriple,
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"-c", swiftBuildConfig,
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"--disable-sandbox"
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)
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outputs.dir(generatedLibraryJavaDir)
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outputs.dir(generatedDemoJavaDir)
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outputs.file(File(swiftBuildDir, "libSwiftAndroidApp.so"))
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// `swift build` is incremental itself; let it decide what is stale.
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outputs.upToDateWhen { false }
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}
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// SwiftKitCore is consumed as source (swift-java is not published to Maven),
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// minus two annotations that pull in `jdk.jfr` (Java Flight Recorder), which
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// is unavailable on Android. `Unsigned` (which the generated bindings DO
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// reference) is replaced by an Android-compatible copy in `src/main/java`.
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val patchedSwiftKitCoreDir = layout.buildDirectory.dir("swiftkitcore-java")
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val stageSwiftKitCore = tasks.register<Sync>("stageSwiftKitCore") {
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dependsOn(jextract)
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from(swiftKitCoreDir)
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exclude(
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"org/swift/swiftkit/core/annotations/ThreadSafe.java",
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"org/swift/swiftkit/core/annotations/Unsigned.java"
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)
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into(patchedSwiftKitCoreDir)
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}
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// Stage the cross-compiled libraries, the swift-java runtime, the Swift
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// Android runtime and libc++_shared into jniLibs so they end up in the APK.
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val stageJniLibs = tasks.register<Copy>("stageJniLibs") {
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dependsOn(jextract)
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into(layout.projectDirectory.dir("src/main/jniLibs/$swiftAbi"))
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from(swiftBuildDir) {
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// Every dynamic library product built by the package graph — anything
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// less leaves a dangling `dlopen` at runtime.
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include("*.so")
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}
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from(swiftAndroidRuntimeDir) {
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include("*.so")
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// Test-only runtime libraries are not needed by the app.
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exclude("*Testing*", "libXCTest.so")
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}
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from(File(swiftAndroidSysroot, "usr/lib/aarch64-linux-android")) {
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include("libc++_shared.so")
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}
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}
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android {
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namespace = "com.pureswift.swiftandroid"
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compileSdk = 35
@@ -16,7 +121,7 @@ android {
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versionName = "1.0"
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ndk {
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//noinspection ChromeOsAbiSupport
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abiFilters += listOf("arm64-v8a")
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abiFilters += listOf(swiftAbi)
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}
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testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
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}
@@ -40,6 +145,12 @@ android {
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buildFeatures {
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compose = true
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}
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// Generated JNI bindings + the (patched) SwiftKitCore Java runtime.
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sourceSets["main"].java.srcDir(generatedLibraryJavaDir)
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sourceSets["main"].java.srcDir(generatedDemoJavaDir)
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sourceSets["main"].java.srcDir(patchedSwiftKitCoreDir)
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packaging {
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resources {
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excludes += listOf("/META-INF/{AL2.0,LGPL2.1}")
@@ -54,16 +165,16 @@ android {
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}
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}
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// Compile native Swift code for the demo app with `skip android build`.
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val buildSwift by tasks.registering(Exec::class) {
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group = "build"
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description = "Build native Swift sources for Android"
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workingDir(rootProject.projectDir)
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commandLine("bash", "build-swift.sh")
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// Ensure Swift is built + bindings generated + libs staged before Java or
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// Kotlin compiles (Kotlin also consumes the generated Java bindings).
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tasks.withType<JavaCompile>().configureEach {
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dependsOn(jextract, stageSwiftKitCore)
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}
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tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
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dependsOn(jextract, stageSwiftKitCore)
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}
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tasks.named("preBuild") {
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dependsOn(buildSwift)
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dependsOn(stageJniLibs)
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}
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dependencies {
@@ -75,8 +186,6 @@ dependencies {
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implementation(libs.androidx.ui)
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implementation(libs.androidx.ui.graphics)
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implementation(libs.androidx.ui.tooling.preview)
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implementation(libs.androidx.recyclerview)
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implementation(libs.androidx.navigation.runtime)
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implementation(libs.androidx.material3)
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implementation(libs.material)
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testImplementation(libs.junit)

‎Demo/app/src/main/java/org/swift/swiftkit/core/annotations/Unsigned.java‎

Lines changed: 36 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,36 @@
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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
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// Licensed under Apache License v2.0
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//
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// See LICENSE.txt for license information
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// See CONTRIBUTORS.txt for the list of Swift.org project authors
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//
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// SPDX-License-Identifier: Apache-2.0
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//
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//===----------------------------------------------------------------------===//
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package org.swift.swiftkit.core.annotations;
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import java.lang.annotation.Documented;
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import java.lang.annotation.Retention;
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import java.lang.annotation.RetentionPolicy;
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import java.lang.annotation.Target;
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import static java.lang.annotation.ElementType.*;
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/**
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* Value is of an unsigned numeric type.
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* <p>
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* Android-compatible copy of SwiftKitCore's {@code Unsigned} annotation: the
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* upstream source carries {@code jdk.jfr} annotations that are unavailable on
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* Android, so the original is excluded from the source set and replaced by
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* this one.
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*/
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@Documented
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@Target({TYPE_USE, PARAMETER, FIELD, METHOD})
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@Retention(RetentionPolicy.RUNTIME)
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public @interface Unsigned {
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}

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