Include LinkageTest to avoid accidentally linking Foundation

.github/workflows/pull_request.yml

@@ -268,3 +268,21 @@ jobs:
           SWIFT_VERSION: "${{ matrix.swift_version }}"
       - name: "Verify sample ${{ matrix.sample_app }}"
         run: .github/scripts/validate_sample.sh Samples/${{ matrix.sample_app }}
+
+  linkage-test:
+    name: Linkage test (jammy swift:6.2)
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        jdk_vendor: ['corretto']
+    container:
+      image: swift:6.2-jammy
+    steps:
+      - uses: actions/checkout@v6
+      - name: Prepare CI Environment
+        uses: ./.github/actions/prepare_env
+      - name: Run linkage test
+        run: ./scripts/run-linkage-test.sh
+        env:
+          JAVA_HOME: ${{ env.JAVA_HOME }}

Tests/LinkageTest/Package.swift

@@ -0,0 +1,166 @@
+// swift-tools-version: 6.1
+
+import Foundation
+import PackageDescription
+
+// Note: the JAVA_HOME environment variable must be set to point to where
+// Java is installed, e.g.,
+//   Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home.
+func findJavaHome() -> String {
+  if let home = ProcessInfo.processInfo.environment["JAVA_HOME"] {
+    return home
+  }
+
+  // This is a workaround for envs (some IDEs) which have trouble with
+  // picking up env variables during the build process
+  let path = "\(FileManager.default.homeDirectoryForCurrentUser.path()).java_home"
+  if let home = try? String(contentsOfFile: path, encoding: .utf8) {
+    if let lastChar = home.last, lastChar.isNewline {
+      return String(home.dropLast())
+    }
+
+    return home
+  }
+
+  if let home = getJavaHomeFromLibexecJavaHome(),
+    !home.isEmpty
+  {
+    return home
+  }
+
+  if let home = getJavaHomeFromSDKMAN() {
+    return home
+  }
+
+  if let home = getJavaHomeFromPath() {
+    return home
+  }
+
+  if ProcessInfo.processInfo.environment["SPI_PROCESSING"] == "1"
+    && ProcessInfo.processInfo.environment["SPI_BUILD"] == nil
+  {
+    return ""
+  }
+  fatalError("Please set the JAVA_HOME environment variable to point to where Java is installed.")
+}
+
+/// On MacOS we can use the java_home tool as a fallback if we can't find JAVA_HOME environment variable.
+func getJavaHomeFromLibexecJavaHome() -> String? {
+  let task = Process()
+  task.executableURL = URL(fileURLWithPath: "/usr/libexec/java_home")
+
+  guard FileManager.default.fileExists(atPath: task.executableURL!.path) else {
+    return nil
+  }
+
+  let pipe = Pipe()
+  task.standardOutput = pipe
+  task.standardError = pipe
+
+  do {
+    try task.run()
+    task.waitUntilExit()
+
+    let data = pipe.fileHandleForReading.readDataToEndOfFile()
+    let output = String(data: data, encoding: .utf8)?.trimmingCharacters(in: .whitespacesAndNewlines)
+
+    if task.terminationStatus == 0 {
+      return output
+    } else {
+      return nil
+    }
+  } catch {
+    return nil
+  }
+}
+
+func getJavaHomeFromSDKMAN() -> String? {
+  let home = FileManager.default.homeDirectoryForCurrentUser
+    .appendingPathComponent(".sdkman/candidates/java/current")
+
+  let javaBin = home.appendingPathComponent("bin/java").path
+  if FileManager.default.isExecutableFile(atPath: javaBin) {
+    return home.path
+  }
+  return nil
+}
+
+func getJavaHomeFromPath() -> String? {
+  let task = Process()
+  task.executableURL = URL(fileURLWithPath: "/usr/bin/which")
+  task.arguments = ["java"]
+
+  let pipe = Pipe()
+  task.standardOutput = pipe
+
+  do {
+    try task.run()
+    task.waitUntilExit()
+    guard task.terminationStatus == 0 else { return nil }
+
+    let data = pipe.fileHandleForReading.readDataToEndOfFile()
+    guard
+      let javaPath = String(data: data, encoding: .utf8)?
+        .trimmingCharacters(in: .whitespacesAndNewlines),
+      !javaPath.isEmpty
+    else { return nil }
+
+    let resolved = URL(fileURLWithPath: javaPath).resolvingSymlinksInPath()
+    return
+      resolved
+      .deletingLastPathComponent()
+      .deletingLastPathComponent()
+      .path
+  } catch {
+    return nil
+  }
+}
+
+let javaHome = findJavaHome()
+
+let javaIncludePath = "\(javaHome)/include"
+#if os(Linux)
+let javaPlatformIncludePath = "\(javaIncludePath)/linux"
+#elseif os(macOS)
+let javaPlatformIncludePath = "\(javaIncludePath)/darwin"
+#elseif os(Windows)
+let javaPlatformIncludePath = "\(javaIncludePath)/win32"
+#endif
+
+let package = Package(
+  name: "linkage-test",
+  dependencies: [
+    .package(name: "swift-java", path: "../..")
+  ],
+  targets: [
+    .executableTarget(
+      name: "LinkageTest",
+      dependencies: [
+        .product(name: "SwiftJava", package: "swift-java")
+      ],
+      swiftSettings: [
+        .unsafeFlags(["-I\(javaIncludePath)", "-I\(javaPlatformIncludePath)"])
+      ],
+      linkerSettings: [
+        .unsafeFlags(
+          [
+            "-L\(javaHome)/lib/server",
+            "-Xlinker", "-rpath",
+            "-Xlinker", "\(javaHome)/lib/server",
+          ],
+          .when(platforms: [.linux, .macOS])
+        ),
+        .unsafeFlags(
+          [
+            "-L\(javaHome)/lib"
+          ],
+          .when(platforms: [.windows])
+        ),
+        .linkedLibrary(
+          "jvm",
+          .when(platforms: [.linux, .macOS, .windows])
+        ),
+      ]
+    )
+  ]
+)

Tests/LinkageTest/Sources/LinkageTest/main.swift

@@ -0,0 +1,19 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024-2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftJava
+
+let _ = try? JavaVirtualMachine.shared()
+let _ = SwiftPlatform.debugOrRelease
+print("Linkage test passed: SwiftJava imported successfully.")

scripts/run-linkage-test.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift.org open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift.org project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of Swift.org project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+set -eu
+
+# Validate that we're running on Linux
+if [[ "$(uname -s)" != "Linux" ]]; then
+    echo "Error: This script must be run on Linux. Current OS: $(uname -s)" >&2
+    exit 1
+fi
+
+echo "Detected JAVA_HOME=${JAVA_HOME}"
+
+echo "Running on Linux - proceeding with linkage test..."
+
+# Build the linkage test package
+echo "Building linkage test package..."
+swift build --package-path Tests/LinkageTest
+
+# Construct build path
+build_path=$(swift build --package-path Tests/LinkageTest --show-bin-path)
+binary_path="$build_path/LinkageTest"
+
+# Verify the binary exists
+if [[ ! -f "$binary_path" ]]; then
+    echo "Error: Built binary not found at $binary_path" >&2
+    exit 1
+fi
+
+echo "Checking linkage for binary: $binary_path"
+
+# Run ldd and check if libFoundation.so is linked
+ldd_output=$(ldd "$binary_path")
+echo "LDD output:"
+echo "$ldd_output"
+
+if echo "$ldd_output" | grep -q "libFoundation.so"; then
+    echo "Error: Binary is linked against libFoundation.so - this indicates incorrect linkage. Ensure the full Foundation is not linked on Linux when FoundationEssentials is available." >&2
+    exit 1
+else
+    echo "Success: Binary is not linked against libFoundation.so - linkage test passed."
+fi