[layout] allow to dump ELK tree for debugging

Fixes #46

org.eclipse.sprotty.layout/src/main/java/org/eclipse/sprotty/layout/ElkLayoutEngine.java

@@ -65,7 +65,7 @@
  * <p>The layout engine must be initialized once during the lifecycle of the application by calling
  * {@link #initialize(ILayoutMetaDataProvider...)}. The arguments of that method should be all meta data
  * providers of the layout algorithms that should be used by this layout engine,
- * e.g. {@link org.eclipse.elk.alg.layered.options.LayeredMetaDataProvider}.</p>
+ * e.g. <code>org.eclipse.elk.alg.layered.options.LayeredMetaDataProvider</code>.</p>
  */
 public class ElkLayoutEngine implements ILayoutEngine {
 
@@ -337,7 +337,7 @@ protected void applyBounds(BoundsAware bounds, ElkShape elkShape) {
 	 * This requires the meta data providers of the referenced algorithms to be registered
 	 * using {@link #initialize(ILayoutMetaDataProvider...)} before any layout is performed, e.g. on
 	 * application start. Alternatively, you can use a specific layout algorithm directly, e.g.
-	 * {@link org.eclipse.elk.alg.layered.LayeredLayoutProvider}.
+	 * <code>org.eclipse.elk.alg.layered.LayeredLayoutProvider</code>.
 	 */
 	public void setEngine(IGraphLayoutEngine engine) {
 		if (engine == null)
@@ -557,5 +557,4 @@ public LayoutContext(Action cause) {
 			this.cause = cause;
 		}
 	}
-
 }

org.eclipse.sprotty.layout/src/main/java/org/eclipse/sprotty/layout/ElktSerializer.java

@@ -0,0 +1,82 @@
+/********************************************************************************
+ * Copyright (c) 2019 TypeFox and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+package org.eclipse.sprotty.layout;
+
+import java.io.ByteArrayOutputStream;
+import java.lang.reflect.Method;
+import java.nio.charset.Charset;
+
+import javax.inject.Inject;
+import javax.inject.Provider;
+
+import org.apache.log4j.Logger;
+import org.eclipse.elk.graph.ElkNode;
+import org.eclipse.emf.common.util.URI;
+import org.eclipse.emf.ecore.resource.Resource;
+import org.eclipse.emf.ecore.resource.impl.ResourceSetImpl;
+
+
+/**
+ * Allows to dump an ELK model in ELKT, such that it can be debugged in
+ * https://rtsys.informatik.uni-kiel.de/elklive/elkgraph.html
+ *
+ * This class needs the Maven artifact
+ *   groupID: org.eclipse.elk
+ *   artifactId: org.eclipse.elk.graph.text
+ * on the classpath.
+ */
+public class ElktSerializer {
+
+	private static final Logger LOG = Logger.getLogger(ElktSerializer.class);
+
+	protected Provider<ResourceSetImpl> resourceSetProvider;
+
+    @Inject
+    public void setResourceSetProvider(Provider<ResourceSetImpl> resourceSetProvider) {
+        this.resourceSetProvider = resourceSetProvider;
+    }
+
+	/**
+	 * Serlialize the given ELK model to ELKT
+	 */
+	public String toElkt(ElkNode node) {
+		try (ByteArrayOutputStream baos = new ByteArrayOutputStream(32768)) {
+			registerElkt();
+			Resource resource = resourceSetProvider.get().createResource(URI.createURI("dump.elkt"));
+			resource.getContents().add(node);
+			resource.save(baos, null);
+			String text = new String(baos.toByteArray(), Charset.defaultCharset());
+			return text;
+		} catch (Throwable exc) {
+			LOG.error("Error serializing ELK model", exc);
+		}
+		return null;
+	}
+
+	/**
+	 * Makes sure ELKT is registered to the EMF registries.
+	 */
+	protected void registerElkt() throws Exception {
+		Object factory = Resource.Factory.Registry.INSTANCE.getExtensionToFactoryMap().get("elkt");
+		if (factory == null) {
+			Class<?> standaloneSetupClass = Class.forName("org.eclipse.elk.graph.text.ElkGraphStandaloneSetup");
+			if (standaloneSetupClass == null)
+				throw new IllegalStateException("'ElkGraphStandaloneSetup' is not on the classpath. Add 'org.eclipse.elk:org.eclipse.elk.graph.text' to your classpath.");
+			Method doSetupMethod = standaloneSetupClass.getMethod("doSetup");
+			doSetupMethod.invoke(null);
+		}
+	}
+}