use formatDocument as fallback for willSaveWaitUntil

if server does not support willSaveWaitUntil the code can be formatted
prior to save.

fixes #761

org.eclipse.lsp4e/.project

@@ -25,6 +25,11 @@
 			<arguments>
 			</arguments>
 		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.pde.ds.core.builder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
 	</buildSpec>
 	<natures>
 		<nature>org.eclipse.m2e.core.maven2Nature</nature>

org.eclipse.lsp4e/META-INF/MANIFEST.MF

@@ -57,3 +57,4 @@ Bundle-Vendor: Eclipse.org
 Import-Package: com.google.common.base,
  com.google.gson;version="2.7.0"
 Automatic-Module-Name: org.eclipse.lsp4e
+Service-Component: OSGI-INF/org.eclipse.lsp4e.DefaultFormatOnSave.xml

org.eclipse.lsp4e/OSGI-INF/org.eclipse.lsp4e.DefaultFormatOnSave.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.1.0" name="org.eclipse.lsp4e.DefaultFormatOnSave">
+   <property name="service.ranking" type="Integer" value="0"/>
+   <implementation class="org.eclipse.lsp4e.DefaultFormatOnSave"/>
+   <service>
+      <provide interface="org.eclipse.lsp4e.IFormatOnSave"/>
+   </service>
+</scr:component>

org.eclipse.lsp4e/build.properties

@@ -7,5 +7,6 @@ bin.includes = META-INF/,\
                icons/,\
                .options,\
                resources/,\
-               schema/
+               schema/,\
+               OSGI-INF/
 src.includes = schema/

org.eclipse.lsp4e/src/org/eclipse/lsp4e/DefaultFormatOnSave.java

@@ -0,0 +1,36 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Contributors to the Eclipse Foundation.
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *   See git history
+ *******************************************************************************/
+package org.eclipse.lsp4e;
+
+import org.eclipse.core.filebuffers.ITextFileBuffer;
+import org.eclipse.jface.text.IDocument;
+import org.eclipse.jface.text.IRegion;
+import org.eclipse.jface.text.Region;
+import org.osgi.service.component.annotations.Component;
+
+@Component(property = { "service.ranking:Integer=0" })
+public class DefaultFormatOnSave implements IFormatOnSave {
+
+	@Override
+	public boolean isEnabledFor(IDocument document) {
+		return false;
+	}
+
+	/**
+	 * Formats the full file
+	 */
+	@Override
+	public IRegion[] getFormattingRegions(ITextFileBuffer buffer) {
+		return new IRegion[] { new Region(0, buffer.getDocument().getLength()) };
+	}
+
+}

org.eclipse.lsp4e/src/org/eclipse/lsp4e/DocumentContentSynchronizer.java

@@ -16,6 +16,7 @@
 import java.io.File;
 import java.net.URI;
 import java.util.Collections;
+import java.util.ConcurrentModificationException;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
@@ -31,13 +32,17 @@
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IPath;
 import org.eclipse.core.runtime.Path;
+import org.eclipse.core.runtime.ServiceCaller;
 import org.eclipse.core.runtime.content.IContentType;
 import org.eclipse.jdt.annotation.NonNull;
 import org.eclipse.jface.preference.IPreferenceStore;
 import org.eclipse.jface.text.BadLocationException;
 import org.eclipse.jface.text.DocumentEvent;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.IDocumentListener;
+import org.eclipse.jface.text.IRegion;
+import org.eclipse.jface.text.MultiTextSelection;
+import org.eclipse.lsp4e.operations.format.LSPFormatter;
 import org.eclipse.lsp4e.ui.Messages;
 import org.eclipse.lsp4j.DidChangeTextDocumentParams;
 import org.eclipse.lsp4j.DidCloseTextDocumentParams;
@@ -65,12 +70,16 @@ final class DocumentContentSynchronizer implements IDocumentListener {
 	private final @NonNull IDocument document;
 	private final @NonNull URI fileUri;
 	private final TextDocumentSyncKind syncKind;
+	private final LSPFormatter formatter = new LSPFormatter();
 
 	private int version = 0;
 	private DidChangeTextDocumentParams changeParams;
 	private long openSaveStamp;
 	private IPreferenceStore store;
 
+
+	private final ServiceCaller<IFormatOnSave> formatOnSave = new ServiceCaller<>(getClass(), IFormatOnSave.class);
+
 	public DocumentContentSynchronizer(@NonNull LanguageServerWrapper languageServerWrapper,
 			@NonNull LanguageServer languageServer,
 			@NonNull IDocument document, TextDocumentSyncKind syncKind) {
@@ -221,6 +230,9 @@ private int lsToWillSaveWaitUntilTimeout() {
 
 	public void documentAboutToBeSaved() {
 		if (!serverSupportsWillSaveWaitUntil()) {
+			if (formatOnSave != null) {
+				formatOnSave.call(f -> formatDocument(f.isEnabledFor(document), f.getFormattingRegions(LSPEclipseUtils.toBuffer(document))));
+			}
 			return;
 		}
 
@@ -257,6 +269,27 @@ public void documentAboutToBeSaved() {
 		}
 	}
 
+	private void formatDocument(boolean enable, IRegion[] formattingRegions) {
+		if (enable && document != null && formattingRegions != null) {
+			try {
+				var textSelection = new MultiTextSelection(document, formattingRegions);
+				formatter.requestFormatting(document, textSelection).get(lsToWillSaveWaitUntilTimeout(), TimeUnit.SECONDS)
+						.ifPresent(edits -> {
+							try {
+								edits.apply();
+							} catch (final ConcurrentModificationException ex) {
+								ServerMessageHandler.showMessage(Messages.LSPFormatHandler_DiscardedFormat, new MessageParams(MessageType.Error, Messages.LSPFormatHandler_DiscardedFormatResponse));
+							} catch (BadLocationException e) {
+								LanguageServerPlugin.logError(e);
+							}
+						});
+			} catch (BadLocationException | InterruptedException | ExecutionException
+					| TimeoutException e) {
+				LanguageServerPlugin.logError(e);
+			}
+		}
+	}
+
 	public void documentSaved(IFileBuffer buffer) {
 		if (openSaveStamp >= buffer.getModificationStamp()) {
 			return;

org.eclipse.lsp4e/src/org/eclipse/lsp4e/IFormatOnSave.java

@@ -0,0 +1,34 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Contributors to the Eclipse Foundation.
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *   See git history
+ *******************************************************************************/
+package org.eclipse.lsp4e;
+
+import org.eclipse.core.filebuffers.ITextFileBuffer;
+import org.eclipse.jface.text.IDocument;
+import org.eclipse.jface.text.IRegion;
+
+public interface IFormatOnSave {
+
+	/**
+	 * Checks whether formatting shall be performed prior to file buffer saving.
+	 * @param document
+	 * @return true if document buffer shall be formatted prior saving
+	 */
+	boolean isEnabledFor(IDocument document);
+
+	/**
+	 * Get the regions to be formatted (e.g. full file, lines edited this session, lines edited vs. source control baseline).
+	 * @param buffer the buffer to compare contents from
+	 * @return regions to be formatted before saving.
+	 */
+	IRegion[] getFormattingRegions(ITextFileBuffer buffer);
+
+}

org.eclipse.lsp4e/src/org/eclipse/lsp4e/LSPEclipseUtils.java

@@ -355,7 +355,7 @@ public static CallHierarchyPrepareParams toCallHierarchyPrepareParams(int offset
 
 	}
 
-	private static ITextFileBuffer toBuffer(IDocument document) {
+	public static ITextFileBuffer toBuffer(IDocument document) {
 		ITextFileBufferManager bufferManager = FileBuffers.getTextFileBufferManager();
 		if (bufferManager == null)
 			return null;