Use always latest toolchain and only run tests in old JVMs

.github/workflows/main.yml

@@ -12,15 +12,12 @@ jobs:
       - uses: actions/setup-java@v5
         with:
           distribution: temurin
-          # The target JDK is used to build, the latest one to run Gradle itself (we cannot use Java 8 for Gradle)
+          # Being in the last position, the latest JDK is used by default to build, the version from the matrix is made
+          # available to run the tests, to check compatibility.
           java-version: |
             ${{ matrix.java-version }}
             21
 
-      # delete gradle.properties in Java 8 because it contains a then-unsupported JVM argument: --add-exports
-      - run: rm gradle.properties
-        if: ${{ matrix.java-version == 8 }}
-
       - run: ./gradlew assemble check --info
         env:
-          JAVA_TOOLCHAIN: ${{ matrix.java-version }}
+          TEST_JAVA_TOOLCHAIN: ${{ matrix.java-version }}

build.gradle

@@ -6,28 +6,16 @@ plugins {
     id "com.diffplug.spotless" version "7.2.1"
 }
 
-var javaToolchain = System.getenv('JAVA_TOOLCHAIN')
-
-java {
-    if (javaToolchain != null) {
-        toolchain {
-            languageVersion = JavaLanguageVersion.of(javaToolchain)
-        }
-    }
-}
-
 compileJava {
-    if (javaToolchain != "8") {
-        options.release = 8
-    }
-    options.compilerArgs.add('-Xlint')
+    options.release = 8
+    // for some reason javac warns the previous option, disabling
+    options.compilerArgs.add('-Xlint:all,-options')
 }
 
 compileTestJava {
-    if (javaToolchain != "8") {
-        options.release = 8
-    }
-    options.compilerArgs.add('-Xlint')
+    options.release = 8
+    // for some reason javac warns the previous option, disabling
+    options.compilerArgs.add('-Xlint:all,-options')
 }
 
 repositories {
@@ -48,6 +36,17 @@ testing {
     suites {
         test {
             useJUnitJupiter()
+            targets {
+                all {
+                    testTask.configure {
+                        javaLauncher.set(
+                                javaToolchains.launcherFor {
+                                    languageVersion.set(JavaLanguageVersion.of(System.getenv('TEST_JAVA_TOOLCHAIN')))
+                                }
+                        )
+                    }
+                }
+            }
         }
     }
 }

src/test/java/lbmq/VersionLoggerTest.java

@@ -0,0 +1,14 @@
+package lbmq;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Not really a test, but a way of confirming that tests are running with the intended JVM version.
+ */
+public class VersionLoggerTest {
+
+    @Test
+    public void versionLogger() {
+        System.out.printf("Running in JVM version %s\n", System.getProperty("java.version"));
+    }
+}