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docc documentation, first step
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‎Package.swift‎

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@@ -210,10 +210,12 @@ let package = Package(
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],
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targets: [
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.target(
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name: "Documentation",
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name: "SwiftJavaDocumentation",
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dependencies: [
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"JavaKit",
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"SwiftKitSwift",
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"SwiftJavaTool",
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]
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),
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‎Sources/Documentation/Documentation.docc/Documentation.md‎

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# Swift Java Interoperability
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@Metadata {
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@TechnologyRoot
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}
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## Overview
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This project contains a number of support packages, java libraries, tools and plugins that provide a complete
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Swift and Java interoperability story.
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Please refer to articles about the specific direction of interoperability you are interested in.
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## Getting started
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TODO: Some general intro
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If you prefer a video introduction, you may want to this
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[Explore Swift and Java interoperability](https://www.youtube.com/watch?v=QSHO-GUGidA)
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WWDC 2025 session,
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which is a quick overview of all the features and approaches offered by SwiftJava.
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## Topics
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### Supported Features
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- <doc:SupportedFeatures>
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### Source generation
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- <doc:SwiftJavaCommandLineTool>
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- <doc:SwiftPMPlugin>
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### Using Java from Swift
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- JavaKit
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### Using Swift from Java
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- SwiftKitSwift

‎Sources/Documentation/Documentation.docc/SupportedFeatures.md‎

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# Supported Features
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Summary of features supported by the swift-java interoperability libraries and tools.
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## JavaKit Macros
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JavaKit supports both directions of interoperability, using Swift macros and source generation
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(via the `swift-java wrap-java` command).
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### Java -> Swift
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It is possible to use JavaKit macros and the `wrap-java` command to simplify implementing
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Java `native` functions. JavaKit simplifies the type conversions
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> tip: This direction of interoperability is covered in the WWDC2025 session 'Explore Swift and Java interoperability'
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> around the [7-minute mark](https://youtu.be/QSHO-GUGidA?si=vUXxphTeO-CHVZ3L&t=448).
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| Feature | Macro support |
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|--------------------------------------------------|-------------------------|
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| Java `static native` method implemented by Swift | ✅ `@JavaImplementation` |
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| **This list is very work in progress** | |
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### Swift -> Java
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> tip: This direction of interoperability is covered in the WWDC2025 session 'Explore Swift and Java interoperability'
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> around the [10-minute mark](https://youtu.be/QSHO-GUGidA?si=QyYP5-p2FL_BH7aD&t=616).
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| Java Feature | Macro support |
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|----------------------------------------|---------------|
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| Java `class` | ✅ |
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| Java class inheritance | ✅ |
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| Java `abstract class` | TODO |
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| Java `enum` | ❌ |
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| Java methods: `static`, member | ✅ `@JavaMethod` |
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| **This list is very work in progress** | |
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## JExtract: Java -> Swift
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SwiftJava's `swift-java jextract` tool automates generating Java bindings from Swift sources.
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> tip: This direction of interoperability is covered in the WWDC2025 session 'Explore Swift and Java interoperability'
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> around the [14-minute mark](https://youtu.be/QSHO-GUGidA?si=b9YUwAWDWFGzhRXN&t=842).
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| Swift Feature | FFM | JNI |
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|--------------------------------------------------------------------------------------| -------- |-----|
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| | | |
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| Initializers: `class`, `struct` | ✅ | ✅ |
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| Optional Initializers / Throwing Initializers | ❌ | ❌ |
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| Deinitializers: `class`, `struct` | ✅ | ✅ |
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| `enum`, `actor` | ❌ | ❌ |
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| Global Swift `func` | ✅ | ✅ |
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| Class/struct member `func` | ✅ | ✅ |
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| Throwing functions: `func x() throws` | ❌ | ✅ |
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| Typed throws: `func x() throws(E)` | ❌ | ❌ |
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| Stored properties: `var`, `let` (with `willSet`, `didSet`) | ✅ | ✅ |
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| Computed properties: `var` (incl. `throws`) | ✅ / TODO | ✅ |
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| Async functions `func async` and properties: `var { get async {} }` | ❌ | ❌ |
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| Arrays: `[UInt8]`, `[T]` | ❌ | ❌ |
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| Dictionaries: `[String: Int]`, `[K:V]` | ❌ | ❌ |
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| Generic functions | ❌ | ❌ |
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| `Foundation.Data`, `any Foundation.DataProtocol` | ✅ | ❌ |
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| Tuples: `(Int, String)`, `(A, B, C)` | ❌ | ❌ |
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| Protocols: `protocol`, existential parameters `any Collection` | ❌ | ❌ |
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| Optional types: `Int?`, `AnyObject?` | ❌ | ❌ |
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| Primitive types: `Bool`, `Int`, `Int8`, `Int16`, `Int32`, `Int64`, `Float`, `Double` | ✅ | ✅ |
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| Unsigned primitive types: `UInt`, `UInt8`, `UInt16`, `UInt32`, `UInt64` | ❌ | ❌ |
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| String (with copying data) | ✅ | ✅ |
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| Variadic parameters: `T...` | ❌ | ❌ |
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| Parametrer packs / Variadic generics | ❌ | ❌ |
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| Ownership modifiers: `inout`, `borrowing`, `consuming` | ❌ | ❌ |
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| Default parameter values: `func p(name: String = "")` | ❌ | ❌ |
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| Operators: `+`, `-`, user defined | ❌ | ❌ |
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| Subscripts: `subscript()` | ❌ | ❌ |
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| Equatable | ❌ | ❌ |
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| Pointers: `UnsafeRawPointer`, UnsafeBufferPointer (?) | 🟡 | ❌ |
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| Nested types: `struct Hello { struct World {} }` | ❌ | ❌ |
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| Inheritance: `class Caplin: Capybara` | ❌ | ❌ |
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| Closures: `func callMe(maybe: () -> ())` | ❌ | ❌ |
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| Swift type extensions: `extension String { func uppercased() }` | 🟡 | 🟡 |
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| Swift macros (maybe) | ❌ | ❌ |
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| Result builders | ❌ | ❌ |
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| Automatic Reference Counting of class types / lifetime safety | ✅ | ✅ |
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| Value semantic types (e.g. struct copying) | ❌ | ❌ |
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| Opaque types: `func get() -> some Builder`, func take(worker: some Worker) | ❌ | ❌ |
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| Swift concurrency: `func async`, `actor`, `distribued actor` | ❌ | ❌ |
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| | | |
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| | | |
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> tip: The list of features may be incomplete, please file an issue if something is unclear or should be clarified in this table.

‎Sources/Documentation/Documentation.docc/SwiftJavaCommandLineTool.md‎

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# swift-java command line tool
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The `swift-java` command line tool offers multiple ways to interact your Java interoperability enabled projects.
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## Generating Swift bindings to Java libraries
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The `swift-java wrap-java` command.

‎Sources/Documentation/Documentation.docc/SwiftPMPlugin.md‎

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# SwiftJava SwiftPM Plugin
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The `SwiftJavaPlugin` automates <doc:SwiftJavaCommandLineTool> invocations during the build process.
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## Installing the plugin
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To install the SwiftPM plugin in your target of choice include the `swift-java` package dependency:
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```swift
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import Foundation
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let javaHome = findJavaHome()
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let javaIncludePath = "\(javaHome)/include"
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#if os(Linux)
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let javaPlatformIncludePath = "\(javaIncludePath)/linux"
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#elseif os(macOS)
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let javaPlatformIncludePath = "\(javaIncludePath)/darwin"
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#elseif os(Windows)
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let javaPlatformIncludePath = "\(javaIncludePath)/win32"
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#endif
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let package = Package(
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name: "MyProject",
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products: [
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.library(
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name: "JavaKitExample",
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type: .dynamic,
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targets: ["JavaKitExample"]
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),
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],
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dependencies: [
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.package(url: "https://github.com/apple/swift-java", from: "..."),
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],
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targets: [
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.target(
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name: "MyProject",
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dependencies: [
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// ...
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],
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swiftSettings: [
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.unsafeFlags(["-I\(javaIncludePath)", "-I\(javaPlatformIncludePath)"])
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],
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plugins: [
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.plugin(name: "JavaCompilerPlugin", package: "swift-java"),
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.plugin(name: "JExtractSwiftPlugin", package: "swift-java"),
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.plugin(name: "SwiftJavaPlugin", package: "swift-java"),
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]
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),
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]
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)
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```
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```swift
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// Note: the JAVA_HOME environment variable must be set to point to where
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// Java is installed, e.g.,
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// Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home.
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func findJavaHome() -> String {
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if let home = ProcessInfo.processInfo.environment["JAVA_HOME"] {
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print("JAVA_HOME = \(home)")
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return home
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}
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// This is a workaround for envs (some IDEs) which have trouble with
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// picking up env variables during the build process
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let path = "\(FileManager.default.homeDirectoryForCurrentUser.path()).java_home"
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if let home = try? String(contentsOfFile: path, encoding: .utf8) {
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if let lastChar = home.last, lastChar.isNewline {
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return String(home.dropLast())
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}
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return home
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}
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if let home = getJavaHomeFromLibexecJavaHome(),
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!home.isEmpty {
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return home
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}
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fatalError("Please set the JAVA_HOME environment variable to point to where Java is installed.")
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}
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/// On MacOS we can use the java_home tool as a fallback if we can't find JAVA_HOME environment variable.
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func getJavaHomeFromLibexecJavaHome() -> String? {
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let task = Process()
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task.executableURL = URL(fileURLWithPath: "/usr/libexec/java_home")
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// Check if the executable exists before trying to run it
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guard FileManager.default.fileExists(atPath: task.executableURL!.path) else {
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print("/usr/libexec/java_home does not exist")
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return nil
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}
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let pipe = Pipe()
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task.standardOutput = pipe
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task.standardError = pipe // Redirect standard error to the same pipe for simplicity
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do {
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try task.run()
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task.waitUntilExit()
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let data = pipe.fileHandleForReading.readDataToEndOfFile()
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let output = String(data: data, encoding: .utf8)?.trimmingCharacters(in: .whitespacesAndNewlines)
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if task.terminationStatus == 0 {
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return output
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} else {
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print("java_home terminated with status: \(task.terminationStatus)")
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// Optionally, log the error output for debugging
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if let errorOutput = String(data: pipe.fileHandleForReading.readDataToEndOfFile(), encoding: .utf8) {
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print("Error output: \(errorOutput)")
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}
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return nil
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}
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} catch {
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print("Error running java_home: \(error)")
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return nil
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}
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}
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```

‎Sources/Documentation/empty.swift‎

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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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// Empty file, this target is a docs-only target.

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