[https://github.com/eclipse/xtext-eclipse/issues/1221] Serializer.

- Improve the serializeReplacement implementation by modifying the
ReplaceRegion length calculation so that it takes not only the
ICompositeNode.getTotalLength() into account, but considers if the new
text contains additional whitespaces and the old text is also followed
by white spaces, than the whitespaces contained by the original document
is also consumed by the quickfix.
- Implement corresponding SerializerReplacementCalculationTest test case
based on the NoJdtTestLanguage.

Signed-off-by: Tamas Miklossy <miklossy@itemis.de>

org.eclipse.xtext.testlanguages/src/org/eclipse/xtext/testlanguages/noJdt/formatting2/NoJdtTestLanguageFormatter.xtend

@@ -11,11 +11,12 @@ import org.eclipse.xtext.testlanguages.noJdt.noJdt.Model
 class NoJdtTestLanguageFormatter extends AbstractFormatter2 {
 	
 	def dispatch void format(Model model, extension IFormattableDocument document) {
-		// TODO: format HiddenRegions around keywords, attributes, cross references, etc. 
 		for (Greeting greeting : model.getGreetings()) {
 			greeting.format;
 		}
 	}
 
-	// TODO: implement for 
+	def dispatch void format(Greeting greeting, extension IFormattableDocument document) {
+		greeting.append[setNewLines(1, 1, 2)]
+	}
 }

org.eclipse.xtext.testlanguages/xtend-gen/org/eclipse/xtext/testlanguages/noJdt/formatting2/NoJdtTestLanguageFormatter.java

@@ -8,10 +8,12 @@ import org.eclipse.emf.common.util.EList;
 import org.eclipse.emf.ecore.EObject;
 import org.eclipse.xtext.formatting2.AbstractFormatter2;
 import org.eclipse.xtext.formatting2.IFormattableDocument;
+import org.eclipse.xtext.formatting2.IHiddenRegionFormatter;
 import org.eclipse.xtext.resource.XtextResource;
 import org.eclipse.xtext.testlanguages.noJdt.noJdt.Greeting;
 import org.eclipse.xtext.testlanguages.noJdt.noJdt.Model;
 import org.eclipse.xtext.xbase.lib.Extension;
+import org.eclipse.xtext.xbase.lib.Procedures.Procedure1;
 
 @SuppressWarnings("all")
 public class NoJdtTestLanguageFormatter extends AbstractFormatter2 {
@@ -22,25 +24,35 @@ public class NoJdtTestLanguageFormatter extends AbstractFormatter2 {
     }
   }
   
-  public void format(final Object model, final IFormattableDocument document) {
-    if (model instanceof XtextResource) {
-      _format((XtextResource)model, document);
+  protected void _format(final Greeting greeting, @Extension final IFormattableDocument document) {
+    final Procedure1<IHiddenRegionFormatter> _function = (IHiddenRegionFormatter it) -> {
+      it.setNewLines(1, 1, 2);
+    };
+    document.<Greeting>append(greeting, _function);
+  }
+  
+  public void format(final Object greeting, final IFormattableDocument document) {
+    if (greeting instanceof XtextResource) {
+      _format((XtextResource)greeting, document);
       return;
-    } else if (model instanceof Model) {
-      _format((Model)model, document);
+    } else if (greeting instanceof Greeting) {
+      _format((Greeting)greeting, document);
       return;
-    } else if (model instanceof EObject) {
-      _format((EObject)model, document);
+    } else if (greeting instanceof Model) {
+      _format((Model)greeting, document);
       return;
-    } else if (model == null) {
+    } else if (greeting instanceof EObject) {
+      _format((EObject)greeting, document);
+      return;
+    } else if (greeting == null) {
       _format((Void)null, document);
       return;
-    } else if (model != null) {
-      _format(model, document);
+    } else if (greeting != null) {
+      _format(greeting, document);
       return;
     } else {
       throw new IllegalArgumentException("Unhandled parameter types: " +
-        Arrays.<Object>asList(model, document).toString());
+        Arrays.<Object>asList(greeting, document).toString());
     }
   }
 }

org.eclipse.xtext.tests/src/org/eclipse/xtext/serializer/SerializerReplacementCalculationTest.java

@@ -0,0 +1,46 @@
+/*******************************************************************************
+ * Copyright (c) 2020 itemis AG (http://www.itemis.eu) and others.
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ * 
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package org.eclipse.xtext.serializer;
+
+import org.eclipse.xtext.resource.SaveOptions;
+import org.eclipse.xtext.testlanguages.noJdt.NoJdtTestLanguageStandaloneSetup;
+import org.eclipse.xtext.testlanguages.noJdt.noJdt.Greeting;
+import org.eclipse.xtext.testlanguages.noJdt.noJdt.Model;
+import org.eclipse.xtext.tests.AbstractXtextTests;
+import org.eclipse.xtext.util.ReplaceRegion;
+import org.junit.Test;
+
+/**
+ * @author miklossy - Initial contribution and API
+ */
+public class SerializerReplacementCalculationTest extends AbstractXtextTests {
+
+	@Override
+	public void setUp() throws Exception {
+		super.setUp();
+		with(NoJdtTestLanguageStandaloneSetup.class);
+	}
+
+	@Test
+	public void testSerializeReplacement001() throws Exception {
+		// Given
+		String textModel = "Hello Xtext!" + System.lineSeparator();
+		StringBuilder stringBuilder = new StringBuilder(textModel);
+		Model model = (Model) getModel(textModel);
+		Greeting greeting = model.getGreetings().get(0);
+		ReplaceRegion replacement =  getSerializer().serializeReplacement(greeting, SaveOptions.defaultOptions());
+
+		// When
+		replacement.applyTo(stringBuilder);
+
+		// Then
+		assertEquals(textModel, stringBuilder.toString());
+	}
+
+}

org.eclipse.xtext/src/org/eclipse/xtext/serializer/impl/Serializer.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2011, 2017 itemis AG (http://www.itemis.eu) and others.
+ * Copyright (c) 2011, 2020 itemis AG (http://www.itemis.eu) and others.
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
@@ -23,6 +23,8 @@ import org.eclipse.xtext.formatting2.regionaccess.ITextRegionAccess;
 import org.eclipse.xtext.formatting2.regionaccess.ITextReplacement;
 import org.eclipse.xtext.formatting2.regionaccess.TextRegionAccessBuilder;
 import org.eclipse.xtext.nodemodel.ICompositeNode;
+import org.eclipse.xtext.nodemodel.ILeafNode;
+import org.eclipse.xtext.nodemodel.INode;
 import org.eclipse.xtext.nodemodel.util.NodeModelUtils;
 import org.eclipse.xtext.parsetree.reconstr.ITokenStream;
 import org.eclipse.xtext.parsetree.reconstr.impl.TokenStringBuffer;
@@ -43,6 +45,7 @@ import org.eclipse.xtext.util.EmfFormatter;
 import org.eclipse.xtext.util.ReplaceRegion;
 import org.eclipse.xtext.validation.IConcreteSyntaxValidator;
 
+import com.google.common.base.CharMatcher;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 
@@ -210,7 +213,60 @@ public class Serializer implements ISerializer {
 			throw new IllegalStateException("Cannot replace an obj that has no associated node");
 		}
 		String text = serialize(obj, options);
-		return new ReplaceRegion(node.getTotalOffset(), node.getTotalLength(), text);
+		int replaceRegionLength = calculateReplaceRegionLength(node, text);
+		return new ReplaceRegion(node.getTotalOffset(), replaceRegionLength, text);
 	}
 
+	/**
+	 * @since 2.22
+	 */
+	protected int calculateReplaceRegionLength(ICompositeNode node, String text) {
+		int oldTextLength = node.getTotalLength();
+		int newTextLength = text.length();
+
+		if (newTextLength > oldTextLength) {
+			String remainingText = text.substring(oldTextLength);
+			if (isWhitespace(remainingText) && hiddenNodeFollows(node)) {
+				return newTextLength;
+			}
+		}
+		return oldTextLength;
+	}
+
+	/**
+	 * @since 2.22
+	 */
+	protected boolean hiddenNodeFollows(ICompositeNode node) {
+		INode followingNode = getFollowingNode(node);
+		if (followingNode instanceof ILeafNode) {
+			return ((ILeafNode)followingNode).isHidden();
+		}
+		return false;
+	}
+	
+	/**
+	 * Returns the node that follows the <i>node</i>, independently, if they have the same parent.
+	 * @since 2.22
+	 */
+	protected INode getFollowingNode(ICompositeNode node) {
+		if (node != null) {
+			if (node.hasNextSibling()) {
+				INode nextSibling = node.getNextSibling();
+				Iterator<ILeafNode> nextSiblingLeafNodes = nextSibling.getLeafNodes().iterator();
+				if (nextSiblingLeafNodes.hasNext()) {
+					return nextSiblingLeafNodes.next();
+				} else {
+					return getFollowingNode(node.getParent());
+				}	
+			}
+		}
+		return null;
+	}
+
+	/**
+	 * @since 2.22
+	 */
+	protected boolean isWhitespace(String text) {
+		return CharMatcher.whitespace().matchesAllOf(text);
+	}
 }