build: Make use of Gradle's Java Toolchains feature

This change updates the build configuration for Gradle to make use of
its Java Toolchains feature which enables running/testing multiple Java
versions at the same time. This feature can also provision a Java
installation if it is not available on the user's system.

5 files changed, 51 insertions, 31 deletions

diff --git a/buildSrc/src/main/kotlin/Libs.kt b/buildSrc/src/main/kotlin/Libs.kt
index 97dc36ca..09432b06 100644
--- a/buildSrc/src/main/kotlin/Libs.kt
+++ b/buildSrc/src/main/kotlin/Libs.kt
@@ -24,32 +24,27 @@
 
 import org.gradle.api.JavaVersion
 import org.gradle.api.Project
+import org.gradle.api.artifacts.VersionCatalog
 import org.gradle.api.artifacts.VersionCatalogsExtension
 import org.gradle.kotlin.dsl.getByType
 
 /**
- * This class makes the version catalog accessible for the build scripts until Gradle adds support for it.
- *
- * See https://github.com/gradle/gradle/issues/15383
+ * Obtain the default [VersionCatalog] of the project.
  */
-public class Libs(project: Project) {
-    /**
-     * The version catalog of the project.
-     */
-    private val versionCatalog = project.extensions.getByType(VersionCatalogsExtension::class).named("libs")
+public val Project.defaultVersionCatalog: VersionCatalog
+    get() = project.extensions.getByType(VersionCatalogsExtension::class).named("libs")
 
-    /**
-     * Obtain the version for the specified [dependency][name].
-     */
-    operator fun get(name: String): String {
-        val dep = versionCatalog.findLibrary(name).get().get()
-        return "${dep.module.group}:${dep.module.name}:${dep.versionConstraint.displayName}"
-    }
+/**
+ * Obtain the dependency string for the specified [name].
+ */
+public operator fun VersionCatalog.get(name: String): String {
+    val dep = findLibrary(name).get().get()
+    return "${dep.module.group}:${dep.module.name}:${dep.versionConstraint.displayName}"
+}
 
-    companion object {
-        /**
-         * The JVM version to target.
-         */
-        val jvmTarget = JavaVersion.VERSION_17
-    }
+/**
+ * Obtain the string representation of the version with the given [name].
+ */
+public fun VersionCatalog.getVersion(name: String): String {
+    return findVersion(name).get().displayName
 }
diff --git a/buildSrc/src/main/kotlin/benchmark-conventions.gradle.kts b/buildSrc/src/main/kotlin/benchmark-conventions.gradle.kts
index 554d2279..e16733a4 100644
--- a/buildSrc/src/main/kotlin/benchmark-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/benchmark-conventions.gradle.kts
@@ -50,7 +50,7 @@ tasks.named("jmh", JMHTask::class) {
 
 dependencies {
     constraints {
-        val libs = Libs(project)
-        jmh(libs["commons.math3"]) // XXX Force JMH to use the same commons-math3 version as OpenDC
+        val versionCatalog = project.defaultVersionCatalog
+        jmh(versionCatalog["commons.math3"]) // XXX Force JMH to use the same commons-math3 version as OpenDC
     }
 }
diff --git a/buildSrc/src/main/kotlin/java-conventions.gradle.kts b/buildSrc/src/main/kotlin/java-conventions.gradle.kts
index 8857d4ab..875ae2a7 100644
--- a/buildSrc/src/main/kotlin/java-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/java-conventions.gradle.kts
@@ -31,8 +31,10 @@ repositories {
 }
 
 java {
-    sourceCompatibility = Libs.jvmTarget
-    targetCompatibility = Libs.jvmTarget
+    toolchain {
+        val javaVersion = project.defaultVersionCatalog.getVersion("java")
+        languageVersion.set(JavaLanguageVersion.of(javaVersion))
+    }
 }
 
 tasks.withType<JavaCompile> {
diff --git a/buildSrc/src/main/kotlin/kotlin-conventions.gradle.kts b/buildSrc/src/main/kotlin/kotlin-conventions.gradle.kts
index 5ccc06a4..79afdf7c 100644
--- a/buildSrc/src/main/kotlin/kotlin-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/kotlin-conventions.gradle.kts
@@ -29,8 +29,15 @@ plugins {
 }
 
 /* Project configuration */
+
+kotlin {
+    jvmToolchain {
+        val javaVersion = project.defaultVersionCatalog.getVersion("java")
+        languageVersion.set(JavaLanguageVersion.of(javaVersion))
+    }
+}
+
 tasks.withType<KotlinCompile>().configureEach {
-    kotlinOptions.jvmTarget = Libs.jvmTarget.toString()
     kotlinOptions.freeCompilerArgs += "-opt-in=kotlin.RequiresOptIn"
     kotlinOptions.freeCompilerArgs += "-Xjvm-default=all"
 }
diff --git a/buildSrc/src/main/kotlin/testing-conventions.gradle.kts b/buildSrc/src/main/kotlin/testing-conventions.gradle.kts
index ebeb58a4..a7fa9da9 100644
--- a/buildSrc/src/main/kotlin/testing-conventions.gradle.kts
+++ b/buildSrc/src/main/kotlin/testing-conventions.gradle.kts
@@ -34,10 +34,26 @@ tasks.test {
 }
 
 dependencies {
-    val libs = Libs(project)
+    val versionCatalog = project.defaultVersionCatalog
 
-    testImplementation(libs["junit.jupiter.api"])
-    testImplementation(libs["junit.jupiter.params"])
-    testImplementation(libs["mockk"])
-    testRuntimeOnly(libs["junit.jupiter.engine"])
+    testImplementation(versionCatalog["junit.jupiter.api"])
+    testImplementation(versionCatalog["junit.jupiter.params"])
+    testImplementation(versionCatalog["mockk"])
+    testRuntimeOnly(versionCatalog["junit.jupiter.engine"])
+}
+
+tasks.register<Test>("testsOn18") {
+    javaLauncher.set(javaToolchains.launcherFor {
+        languageVersion.set(JavaLanguageVersion.of(18))
+    })
+
+    useJUnitPlatform()
+}
+
+tasks.register<Test>("testsOn19") {
+    javaLauncher.set(javaToolchains.launcherFor {
+        languageVersion.set(JavaLanguageVersion.of(19))
+    })
+
+    useJUnitPlatform()
 }