Throw EcjFailureException in performCompile, not in constructor

This shifts the focus from a supposed Maven component wiring error to
the root cause, expressed in the error message: "ECJ needs JRE 17+".

The new static boolean field EclipseJavaCompiler.isJdkSupported also
enables us to write a simple unit test, asserting on the error message,
if the field value is false.

Relates to #347.

Author: kriegaex

plexus-compilers/plexus-compiler-eclipse/src/main/java/org/codehaus/plexus/compiler/eclipse/EclipseJavaCompiler.java

@@ -64,7 +64,7 @@
 public class EclipseJavaCompiler extends AbstractCompiler {
     public EclipseJavaCompiler() {
         super(CompilerOutputStyle.ONE_OUTPUT_FILE_PER_INPUT_FILE, ".java", ".class", null);
-        if (Runtime.version().feature() < 17) throw new EcjFailureException("ECJ only works on Java 17+");
+        if (!isJdkSupported) return;
         try {
             // Do not directly import EclipseJavaCompilerDelegate or any ECJ classes compiled to target 17.
             // This ensures that the plugin still runs on Java 11 and can report the error above.
@@ -82,9 +82,10 @@ public EclipseJavaCompiler() {
     // ----------------------------------------------------------------------
     // Compiler Implementation
     // ----------------------------------------------------------------------
+    static boolean isJdkSupported = Runtime.version().feature() >= 17;
     boolean errorsAsWarnings = false;
-    private final MethodHandle getClassLoaderMH;
-    private final MethodHandle batchCompileMH;
+    private MethodHandle getClassLoaderMH;
+    private MethodHandle batchCompileMH;
 
     @Override
     public String getCompilerId() {
@@ -93,6 +94,8 @@ public String getCompilerId() {
 
     @Override
     public CompilerResult performCompile(CompilerConfiguration config) throws CompilerException {
+        if (!isJdkSupported) throw new EcjFailureException("ECJ needs JRE 17+");
+
         List<String> args = new ArrayList<>();
         args.add("-noExit"); // Make sure ecj does not System.exit on us 8-/
 

plexus-compilers/plexus-compiler-eclipse/src/test/java/org/codehaus/plexus/compiler/eclipse/EclipseCompilerUnsupportedJdkTest.java

@@ -0,0 +1,62 @@
+package org.codehaus.plexus.compiler.eclipse;
+
+import javax.inject.Inject;
+import javax.inject.Named;
+
+import java.io.File;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.codehaus.plexus.compiler.Compiler;
+import org.codehaus.plexus.compiler.CompilerConfiguration;
+import org.codehaus.plexus.testing.PlexusTest;
+import org.codehaus.plexus.util.FileUtils;
+import org.hamcrest.MatcherAssert;
+import org.hamcrest.Matchers;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.Isolated;
+
+import static org.codehaus.plexus.testing.PlexusExtension.getBasedir;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+@PlexusTest
+@Isolated("changes static variable")
+public class EclipseCompilerUnsupportedJdkTest {
+    static final boolean IS_JDK_SUPPORTED = EclipseJavaCompiler.isJdkSupported;
+
+    @Inject
+    @Named("eclipse")
+    Compiler compiler;
+
+    private CompilerConfiguration getConfig() throws Exception {
+        String sourceDir = getBasedir() + "/src/test-input/src/main";
+        Set<File> sourceFiles = FileUtils.getFileNames(new File(sourceDir), "**/*.java", null, false, true).stream()
+                .map(File::new)
+                .collect(Collectors.toSet());
+        CompilerConfiguration compilerConfig = new CompilerConfiguration();
+        compilerConfig.addSourceLocation(sourceDir);
+        compilerConfig.setOutputLocation(getBasedir() + "/target/eclipse/classes");
+        compilerConfig.setSourceFiles(sourceFiles);
+        compilerConfig.setTargetVersion("1.8");
+        compilerConfig.setSourceVersion("1.8");
+        return compilerConfig;
+    }
+
+    @BeforeAll
+    public static void setUpClass() {
+        EclipseJavaCompiler.isJdkSupported = false;
+    }
+
+    @AfterAll
+    public static void cleanUpClass() {
+        EclipseJavaCompiler.isJdkSupported = IS_JDK_SUPPORTED;
+    }
+
+    @Test
+    public void testUnsupportedJdk() {
+        EcjFailureException error = assertThrows(EcjFailureException.class, () -> compiler.performCompile(getConfig()));
+        MatcherAssert.assertThat(error.getEcjOutput(), Matchers.containsString("ECJ needs JRE 17+"));
+    }
+}