Add additional check to ensure Recaf runs with a JDK and not a JRE

For now we'll just exit with a special exit code, since we crash anyways.

Longer term we will want to just disable features that rely on the JDK specific code rather than exit. This includes things like:

- Attaching to remote processes (jdk.attach module does not exist in JREs)
- Recompiling (JavacCompiler interface has no implementations)

recaf-core/src/main/java/software/coley/recaf/ExitCodes.java

@@ -16,5 +16,6 @@ public class ExitCodes {
 	public static final int ERR_FX_UNKNOWN_VERSION = 106;
 	public static final int INTELLIJ_TERMINATION = 130;
 	public static final int ERR_CDI_INIT_FAILURE = 150;
+	public static final int ERR_NOT_A_JDK = 160;
 
 }

recaf-core/src/main/java/software/coley/recaf/services/compile/JavacCompiler.java

@@ -13,7 +13,11 @@
 import software.coley.recaf.workspace.model.Workspace;
 import software.coley.recaf.workspace.model.resource.WorkspaceResource;
 
-import javax.tools.*;
+import javax.tools.Diagnostic;
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileManager;
+import javax.tools.JavaFileObject;
+import javax.tools.ToolProvider;
 import java.lang.invoke.MethodHandle;
 import java.lang.invoke.MethodHandles;
 import java.lang.reflect.Field;
@@ -59,8 +63,8 @@ public JavacCompiler(JavacCompilerConfig config) {
 	 */
 	@Nonnull
 	public CompilerResult compile(@Nonnull JavacArguments arguments,
-								  @Nullable Workspace workspace,
-								  @Nullable JavacListener listener) {
+	                              @Nullable Workspace workspace,
+	                              @Nullable JavacListener listener) {
 		return compile(arguments, workspace, null, listener);
 	}
 
@@ -79,9 +83,9 @@ public CompilerResult compile(@Nonnull JavacArguments arguments,
 	 */
 	@Nonnull
 	public CompilerResult compile(@Nonnull JavacArguments arguments,
-								  @Nullable Workspace workspace,
-								  @Nullable List<WorkspaceResource> supplementaryResources,
-								  @Nullable JavacListener listener) {
+	                              @Nullable Workspace workspace,
+	                              @Nullable List<WorkspaceResource> supplementaryResources,
+	                              @Nullable JavacListener listener) {
 		if (compiler == null)
 			return new CompilerResult(new IllegalStateException("Cannot load 'javac' compiler."));
 
@@ -168,7 +172,7 @@ public static int getMinTargetVersion() {
 	 * @return Listener to encompass recording behavior and the user defined listener.
 	 */
 	private JavacListener createRecordingListener(@Nullable JavacListener listener,
-												  @Nonnull List<CompilerDiagnostic> diagnostics) {
+	                                              @Nonnull List<CompilerDiagnostic> diagnostics) {
 		return new ForwardingListener(listener) {
 			@Override
 			public void report(@Nonnull Diagnostic<? extends JavaFileObject> diagnostic) {

recaf-core/src/main/java/software/coley/recaf/util/JdkValidation.java

@@ -0,0 +1,27 @@
+package software.coley.recaf.util;
+
+import org.slf4j.Logger;
+import software.coley.recaf.ExitCodes;
+import software.coley.recaf.ExitDebugLoggingHook;
+import software.coley.recaf.analytics.logging.Logging;
+
+/**
+ * JDK vs JRE validation utils.
+ *
+ * @author Matt Coley
+ */
+public class JdkValidation {
+	private static final Logger logger = Logging.get(JdkValidation.class);
+
+	/**
+	 * Applies a few assorted checks to ensure we are running on a JDK and not a JRE.
+	 */
+	public static void validateJdk() {
+		try {
+			Class.forName("com.sun.tools.attach.VirtualMachine");
+		} catch (ClassNotFoundException ex) {
+			logger.error("Recaf must be run with a JDK, but was run with a JRE: " + System.getProperty("java.home"));
+			ExitDebugLoggingHook.exit(ExitCodes.ERR_NOT_A_JDK);
+		}
+	}
+}

recaf-ui/src/main/java/software/coley/recaf/Main.java

@@ -21,6 +21,7 @@
 import software.coley.recaf.services.workspace.io.ResourceImporter;
 import software.coley.recaf.ui.config.WindowScaleConfig;
 import software.coley.recaf.util.JFXValidation;
+import software.coley.recaf.util.JdkValidation;
 import software.coley.recaf.util.Lang;
 import software.coley.recaf.workspace.model.BasicWorkspace;
 
@@ -80,6 +81,9 @@ public static void main(String[] args) {
 			}
 		}
 
+		// Validate we're on a JDK and not a JRE
+		JdkValidation.validateJdk();
+
 		// Invoke the bootstrapper, initializing the UI once the container is built.
 		recaf = Bootstrap.get();
 		launchArgs = recaf.get(LaunchArguments.class);