Lower JDK version for modules not using ffm

.github/workflows/pull_request.yml

@@ -221,7 +221,7 @@ jobs:
           'JavaKitSampleApp',
           'JavaProbablyPrime',
           'JavaSieve',
-          'SwiftAndJavaJarSampleLib',
+          'SwiftAndJavaJarFFMSampleLib',
           'SwiftJavaExtractFFMSampleApp',
           'SwiftJavaExtractJNISampleApp',
         ]
@@ -249,7 +249,7 @@ jobs:
           'JavaKitSampleApp',
           'JavaProbablyPrime',
           'JavaSieve',
-          'SwiftAndJavaJarSampleLib',
+          'SwiftAndJavaJarFFMSampleLib',
           'SwiftJavaExtractFFMSampleApp',
           'SwiftJavaExtractJNISampleApp',
         ]

BuildLogic/src/main/kotlin/build-logic.java-common-conventions.gradle.kts

@@ -23,7 +23,7 @@ plugins {
 
 java {
     toolchain {
-        languageVersion = JavaLanguageVersion.of(25)
+        languageVersion = JavaLanguageVersion.of((gradle.extra.properties["swiftJavaJdk"] as? Int) ?: 25)
     }
 }
 

Samples/SwiftAndJavaJarSampleLib/Package.swift → Samples/SwiftAndJavaJarFFMSampleLib/Package.swift

@@ -5,7 +5,7 @@ import CompilerPluginSupport
 import PackageDescription
 
 let package = Package(
-  name: "SwiftAndJavaJarSampleLib",
+  name: "SwiftAndJavaJarFFMSampleLib",
   platforms: [
     .macOS(.v15),
     .iOS(.v18),

Samples/SwiftAndJavaJarSampleLib/build.gradle.kts → Samples/SwiftAndJavaJarFFMSampleLib/build.gradle.kts

@@ -32,7 +32,7 @@ repositories {
 
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(25))
+        languageVersion.set(JavaLanguageVersion.of((gradle.extra.properties["swiftJavaJdk"] as? Int) ?: 17))
     }
 }
 
@@ -85,13 +85,13 @@ tasks.jar.configure {
 }
 
 base {
-    archivesName = "swift-and-java-jar-sample-lib"
+    archivesName = "swift-and-java-jar-ffm-sample-lib"
 }
 
 publishing {
     publications {
         create<MavenPublication>("maven") {
-            artifactId = "swift-and-java-jar-sample-lib"
+            artifactId = "swift-and-java-jar-ffm-sample-lib"
             from(components["java"])
         }
     }

Samples/SwiftAndJavaJarFFMSampleLib/gradle.properties

@@ -0,0 +1 @@
+../gradle.properties

Samples/SwiftJavaExtractFFMSampleApp/build.gradle.kts

@@ -29,7 +29,7 @@ repositories {
 
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(25))
+        languageVersion.set(JavaLanguageVersion.of((gradle.extra.properties["swiftJavaJdk"] as? Int) ?: 25))
     }
 }
 

Samples/SwiftJavaExtractJNISampleApp/build.gradle.kts

@@ -29,7 +29,7 @@ repositories {
 
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(25))
+        languageVersion.set(JavaLanguageVersion.of((gradle.extra.properties["swiftJavaJdk"] as? Int) ?: 17))
     }
 }
 

Samples/SwiftJavaExtractJNISampleApp/src/test/java/com/example/swift/MultipleTypesFromSingleFileTest.java

@@ -18,7 +18,6 @@
 import org.swift.swiftkit.core.ConfinedSwiftMemorySession;
 import org.swift.swiftkit.core.SwiftArena;
 
-import java.lang.foreign.Arena;
 import java.util.Optional;
 import java.util.OptionalInt;
 

Samples/SwiftJavaExtractJNISampleApp/src/test/java/com/example/swift/VehicleEnumTest.java

@@ -18,7 +18,6 @@
 import org.swift.swiftkit.core.ConfinedSwiftMemorySession;
 import org.swift.swiftkit.core.SwiftArena;
 
-import java.lang.foreign.Arena;
 import java.util.Optional;
 import java.util.OptionalInt;
 

SwiftKitCore/build.gradle.kts

@@ -43,12 +43,12 @@ publishing {
 
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(25))
+        languageVersion.set(JavaLanguageVersion.of((gradle.extra.properties["swiftJavaJdk"] as? Int) ?: 25))
     }
 }
 
 tasks.withType<JavaCompile>().configureEach {
-    // Support Java 11
+    // SwiftKitCore is consumable down to Java 11
     options.release.set(11)
 }
 

SwiftKitFFM/build.gradle.kts

@@ -43,7 +43,7 @@ publishing {
 
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(25))
+        languageVersion.set(JavaLanguageVersion.of((gradle.extra.properties["swiftJavaJdk"] as? Int) ?: 25))
     }
 }
 

gradle.properties

@@ -1 +1 @@
-org.gradle.java.installations.fromEnv=JAVA_HOME_25,JAVA_HOME_25_X64,JAVA_HOME_25_ARM64
+org.gradle.java.installations.fromEnv=JAVA_HOME_25,JAVA_HOME_25_X64,JAVA_HOME_25_ARM64,JAVA_HOME_21,JAVA_HOME_21_X64,JAVA_HOME_21_ARM64,JAVA_HOME_17,JAVA_HOME_17_X64,JAVA_HOME_17_ARM64

settings.gradle.kts

@@ -18,16 +18,78 @@ pluginManagement {
 
 rootProject.name = "swift-java"
 
+// ==== -----------------------------------------------------------------------
+// MARK: JDK detection
+//
+// Some modules require JDK 25+ (FFM API). When the active toolchain is
+// older we exclude those modules so developers with only JDK 17 can still
+// build the JDK-17-compatible subset (currently SwiftKitCore).
+//
+// Resolution order:
+//   1. -PswiftJavaJdk=<n> Gradle property (explicit override)
+//   2. JAVA_HOME_25* env vars listed in gradle.properties (treated as 25)
+//   3. JAVA_HOME/release file's JAVA_VERSION
+//   4. Default: 25
+
+fun detectJdkMajor(): Int {
+    settings.providers.gradleProperty("swiftJavaJdk").orNull?.toIntOrNull()?.let { return it }
+
+    val env = System.getenv()
+    if (listOf("JAVA_HOME_25", "JAVA_HOME_25_X64", "JAVA_HOME_25_ARM64").any { env[it] != null }) {
+        return 25
+    }
+
+    env["JAVA_HOME"]?.let { javaHome ->
+        val release = File(javaHome, "release")
+        if (release.isFile) {
+            release.readLines().firstOrNull { it.startsWith("JAVA_VERSION=") }?.let { line ->
+                val raw = line.substringAfter("=").trim().trim('"')
+                val major = raw.substringBefore(".").toIntOrNull()
+                    ?: raw.substringBefore("-").toIntOrNull()
+                if (major != null) return major
+            }
+        }
+    }
+    return 25
+}
+
+val swiftJavaJdk = detectJdkMajor()
+gradle.extra["swiftJavaJdk"] = swiftJavaJdk
+
+val ffmCapable = swiftJavaJdk >= 22
+
+// Modules and samples that depend on the FFM API (java.lang.foreign.*)
+val ffmModules = setOf(
+    "SwiftKitFFM",
+    "SwiftJavaExtractFFMSampleApp",
+    "SwiftAndJavaJarFFMSampleLib",
+)
+
+val skipped = mutableListOf<String>()
+
 include("SwiftKitCore")
-include("SwiftKitFFM")
+if (ffmCapable) {
+    include("SwiftKitFFM")
+} else {
+    skipped += "SwiftKitFFM"
+}
 
 // Include sample apps -- you can run them via `gradle Name:run`
 if (!(settings.providers.gradleProperty("skipSamples").orNull.toBoolean())) {
-    File(rootDir, "Samples").listFiles().forEach {
+    File(rootDir, "Samples").listFiles()?.forEach {
         if (it.isDirectory && (File(it, "build.gradle").exists() || File(it, "build.gradle.kts").exists())) {
-            include(":Samples:${it.name}")
+            val name = it.name
+            if (name in ffmModules && !ffmCapable) {
+                skipped += "Samples:$name"
+            } else {
+                include(":Samples:$name")
+            }
         }
     }
 }
 
+if (skipped.isNotEmpty()) {
+    println("[swift-java] JDK $swiftJavaJdk detected — skipping: ${skipped.joinToString(", ")}")
+}
+
 enableFeaturePreview("TYPESAFE_PROJECT_ACCESSORS")