Fix #269 Keep comments in .flattened-pom.xml

src/main/java/org/codehaus/mojo/flatten/FlattenMojo.java

@@ -367,6 +367,16 @@ public class FlattenMojo
     @Parameter( defaultValue = "${session}", readonly = true, required = true )
     private MavenSession session;
 
+    /**
+     * The core maven model readers/writers are discarding the comments of the pom.xml.
+     * By setting keepCommentsInPom to true the current comments are moved to the flattened pom.xml.
+     * Default value is false (= not re-adding comments).
+     * 
+     * @since 1.3.0
+     */
+    @Parameter( property = "flatten.dependency.keepComments", required = false , defaultValue = "false")
+    private boolean keepCommentsInPom;
+
     @Component
     private DependencyResolver dependencyResolver;
 
@@ -397,19 +407,25 @@ public void execute()
         getLog().info( "Generating flattened POM of project " + this.project.getId() + "..." );
 
         File originalPomFile = this.project.getFile();
+        KeepCommentsInPom commentsOfOriginalPomFile = null;
+        if (keepCommentsInPom) {
+        	commentsOfOriginalPomFile = KeepCommentsInPom.create(getLog(), originalPomFile);
+        }
         Model flattenedPom = createFlattenedPom( originalPomFile );
         String headerComment = extractHeaderComment( originalPomFile );
 
         File flattenedPomFile = getFlattenedPomFile();
-        writePom( flattenedPom, flattenedPomFile, headerComment );
+        writePom( flattenedPom, flattenedPomFile, headerComment , commentsOfOriginalPomFile);
 
         if ( isUpdatePomFile() )
         {
             this.project.setPomFile( flattenedPomFile );
         }
     }
 
-    /**
+
+
+	/**
      * This method extracts the XML header comment if available.
      *
      * @param xmlFile is the XML {@link File} to parse.
@@ -445,7 +461,7 @@ protected String extractHeaderComment( File xmlFile )
      *                      before root tag). May be <code>null</code> if not present and to be omitted in target POM.
      * @throws MojoExecutionException if the operation failed (e.g. due to an {@link IOException}).
      */
-    protected void writePom( Model pom, File pomFile, String headerComment )
+    protected void writePom( Model pom, File pomFile, String headerComment,  KeepCommentsInPom anOriginalCommentsPath )
         throws MojoExecutionException
     {
 
@@ -483,10 +499,16 @@ protected void writePom( Model pom, File pomFile, String headerComment )
                 getLog().warn( "POM XML post-processing failed: no project tag found!" );
             }
         }
-        writeStringToFile( buffer.toString(), pomFile, pom.getModelEncoding() );
+        String xmlString;
+        if (anOriginalCommentsPath == null) {
+        	xmlString = buffer.toString();
+        } else {
+        	xmlString = anOriginalCommentsPath.restoreOriginalComments(buffer.toString(), pom.getModelEncoding());
+        }
+        writeStringToFile( xmlString, pomFile, pom.getModelEncoding() );
     }
 
-    /**
+	/**
      * Writes the given <code>data</code> to the given <code>file</code> using the specified <code>encoding</code>.
      *
      * @param data     is the {@link String} to write.

src/main/java/org/codehaus/mojo/flatten/KeepCommentsInPom.java

@@ -0,0 +1,269 @@
+package org.codehaus.mojo.flatten;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.BiConsumer;
+
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.parsers.ParserConfigurationException;
+
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.logging.Log;
+import org.w3c.dom.Document;
+import org.w3c.dom.Node;
+import org.w3c.dom.NodeList;
+import org.w3c.dom.bootstrap.DOMImplementationRegistry;
+import org.w3c.dom.ls.DOMImplementationLS;
+import org.w3c.dom.ls.LSOutput;
+import org.w3c.dom.ls.LSSerializer;
+import org.xml.sax.SAXException;
+
+/**
+ * Helper class to keep the comments how they have been in the original pom.xml While reading with
+ * {@link org.apache.maven.model.io.xpp3.MavenXpp3Writer} the comments are not placed into the
+ * {@link org.apache.maven.model.Model} and so {@link org.apache.maven.model.io.xpp3.MavenXpp3Writer} is not able to
+ * re-write those comments.
+ * 
+ * Workaround (maybe until core is fixed) is to remember all the comments and restore them after MavenXpp3Writer has
+ * created the new flattened pom.xml.
+ * 
+ * Current restriction on non-unique child nodes is that this class finds the node back due to the position in the file,
+ * that may lead to mis-re-added comments e.g. on multiple added dependencies (but for e.g. resolveCiFriendliesOnly the
+ * nodes keep stable)
+ * 
+ */
+class KeepCommentsInPom
+{
+
+	/**
+	 * Create an instance with collected current comments of the passed pom.xml file.
+	 */
+	static KeepCommentsInPom create(Log aLog, File aOriginalPomFile) throws MojoExecutionException
+	{
+		KeepCommentsInPom tempKeepCommentsInPom = new KeepCommentsInPom();
+		tempKeepCommentsInPom.setLog(aLog);
+		tempKeepCommentsInPom.loadComments(aOriginalPomFile);
+		return tempKeepCommentsInPom;
+	}
+
+	private Log log;
+
+	/**
+	 * The unique path list for an original node (the comments are stored via the referenced previousSibling)
+	 */
+	private Map<String, Node> commentsPaths;
+
+	/**
+	 * 
+	 */
+	KeepCommentsInPom()
+	{
+		super();
+	}
+
+	/**
+	 * load all current comments and text fragments from xml file
+	 * 
+	 * @param anOriginalPomFile the pom.xml
+	 */
+	private void loadComments(File anOriginalPomFile) throws MojoExecutionException
+	{
+		commentsPaths = new HashMap<>();
+		DocumentBuilderFactory tempDBF = DocumentBuilderFactory.newInstance();
+		DocumentBuilder tempDB;
+		try
+		{
+			tempDB = tempDBF.newDocumentBuilder();
+			Document tempPom = tempDB.parse(anOriginalPomFile);
+			Node tempNode = tempPom.getDocumentElement();
+			walkOverNodes(tempNode, ".", (node, nodePath) ->
+			{
+				// collectNodesByPathNames
+				commentsPaths.put(nodePath, node);
+			});
+		} catch (ParserConfigurationException | SAXException | IOException e)
+		{
+			throw new MojoExecutionException("Cannot load comments from " + anOriginalPomFile, e);
+		}
+	}
+
+	/**
+	 * Walk over the pom hierarchy of the Document.
+	 * 
+	 * @param Node      the current Node
+	 * @param String    the unique path in the parent
+	 * @param aConsumer Function to be called with the toBeCollected/found node.
+	 */
+	private void walkOverNodes(Node aNode, String aParentPath, BiConsumer<Node, String> aConsumer)
+	{
+		String tempNodeName = aNode.getNodeName();
+		if (log.isDebugEnabled())
+		{
+			log.debug("walkOverNodes: aParentPath=" + aParentPath + " tempNodeName=" + tempNodeName);
+		}
+		String tempNodePath = aParentPath + "\t" + tempNodeName;
+		aConsumer.accept(aNode, tempNodePath);
+		NodeList tempChilds = aNode.getChildNodes();
+		// Copy the childs as aConsumer may change the node sequence (add a comment)
+		List<Node> tempCopiedChilds = new ArrayList<>();
+		Map<String, Integer> tempChildWithSameName = new HashMap<>();
+		for (int i = 0; i < tempChilds.getLength(); i++)
+		{
+			Node tempItem = tempChilds.item(i);
+			if (tempItem.getNodeType() != Node.TEXT_NODE && tempItem.getNodeType() != Node.COMMENT_NODE)
+			{
+				// Take real nodes to find them back by number
+				String tempChildNodeName = tempItem.getNodeName();
+				Integer tempChildWithSameNameCount = tempChildWithSameName.get(tempChildNodeName);
+				if (tempChildWithSameNameCount == null)
+				{
+					tempChildWithSameNameCount = 1;
+				} else
+				{
+					tempChildWithSameNameCount += 1;
+				}
+				tempChildWithSameName.put(tempChildNodeName, tempChildWithSameNameCount);
+				tempCopiedChilds.add(tempItem);
+			}
+		}
+		Map<String, Integer> tempChildWithSameNameCounters = new HashMap<>();
+		for (int i = 0; i < tempCopiedChilds.size(); i++)
+		{
+			Node tempCopiedChild = tempCopiedChilds.get(i);
+			String tempChildNodeName = tempCopiedChild.getNodeName();
+			if (tempChildWithSameName.get(tempChildNodeName) > 1)
+			{
+				Integer tempChildWithSameNameCounter = tempChildWithSameNameCounters.get(tempChildNodeName);
+				if (tempChildWithSameNameCounter == null)
+				{
+					tempChildWithSameNameCounter = 1;
+				} else
+				{
+					tempChildWithSameNameCounter += 1;
+				}
+				tempChildWithSameNameCounters.put(tempChildNodeName, tempChildWithSameNameCounter);
+				// add a counter to find back the correct node.
+				walkOverNodes(tempCopiedChild, tempNodePath + "\t" + tempChildWithSameNameCounter, aConsumer);
+			} else
+			{
+				// unique child names
+				walkOverNodes(tempCopiedChild, tempNodePath, aConsumer);
+			}
+		}
+	}
+
+	/**
+	 * @param String the XML written by {@link org.apache.maven.model.io.xpp3.MavenXpp3Writer}
+	 */
+	public String restoreOriginalComments(String anXml, String aModelEncoding) throws MojoExecutionException
+	{
+		DocumentBuilderFactory tempDBF = DocumentBuilderFactory.newInstance();
+		DocumentBuilder tempDB;
+		try
+		{
+			tempDB = tempDBF.newDocumentBuilder();
+			String tempEncoding = aModelEncoding == null ? "UTF-8" : aModelEncoding; // default encoding UTF-8 when
+																						// nothing in pom model.
+			Document tempPom = tempDB.parse(new ByteArrayInputStream(anXml.getBytes(tempEncoding)));
+			Node tempNode = tempPom.getDocumentElement();
+			walkOverNodes(tempNode, ".", (newNode, nodePath) ->
+			{
+				Node tempOriginalNode = commentsPaths.get(nodePath);
+				if (tempOriginalNode != null)
+				{
+					String tempOriginalNodeName = tempOriginalNode.getNodeName();
+					if (tempOriginalNodeName.equals(newNode.getNodeName()))
+					{
+						// found matching node
+						Node tempRefChild = newNode;
+						Node tempPotentialCommentOrText = tempOriginalNode.getPreviousSibling();
+						while (tempPotentialCommentOrText != null
+								&& tempPotentialCommentOrText.getNodeType() == Node.TEXT_NODE)
+						{
+							// skip text in the original xml node
+							tempPotentialCommentOrText = tempPotentialCommentOrText.getPreviousSibling();
+						}
+						while (tempPotentialCommentOrText != null
+								&& tempPotentialCommentOrText.getNodeType() == Node.COMMENT_NODE)
+						{
+							// copy the node to be able to call previoussibling for next element
+							Node tempRefPrevious = tempRefChild.getPreviousSibling();
+							String tempWhitespaceTextBeforeRefNode = null;
+							if (tempRefPrevious != null && tempRefPrevious.getNodeType() == Node.TEXT_NODE)
+							{
+								tempWhitespaceTextBeforeRefNode = tempRefPrevious.getNodeValue();
+							}
+							Node tempNewComment;
+							tempNewComment = tempPom.createComment(tempPotentialCommentOrText.getNodeValue());
+							tempRefChild.getParentNode().insertBefore(tempNewComment, tempRefChild);
+							// copy the whitespaces between comment and refNode
+							if (tempWhitespaceTextBeforeRefNode != null)
+							{
+								tempRefChild.getParentNode().insertBefore(
+										tempPom.createTextNode(tempWhitespaceTextBeforeRefNode), tempRefChild);
+							}
+
+							tempRefChild = tempNewComment;
+
+							tempPotentialCommentOrText = tempPotentialCommentOrText.getPreviousSibling();
+							while (tempPotentialCommentOrText != null
+									&& tempPotentialCommentOrText.getNodeType() == Node.TEXT_NODE)
+							{
+								// skip text in the original xml node
+								tempPotentialCommentOrText = tempPotentialCommentOrText.getPreviousSibling();
+							}
+						}
+					}
+				}
+			});
+			return writeDocumentToString(tempPom);
+		} catch (ParserConfigurationException | SAXException | IOException | ClassNotFoundException
+				| InstantiationException | IllegalAccessException | ClassCastException e)
+		{
+			throw new MojoExecutionException("Cannot add  comments", e);
+		}
+	}
+
+	/**
+	 * Use an LSSerializer to keep whitespaces added by MavenXpp3Writer
+	 * 
+	 * @param Document the pom to write to String.
+	 */
+	private String writeDocumentToString(Document aPom)
+			throws ClassNotFoundException, InstantiationException, IllegalAccessException
+	{
+		DOMImplementationRegistry registry = DOMImplementationRegistry.newInstance();
+		DOMImplementationLS impl = (DOMImplementationLS) registry.getDOMImplementation("LS");
+		LSOutput output = impl.createLSOutput();
+		output.setEncoding("UTF-8");
+		ByteArrayOutputStream outStream = new ByteArrayOutputStream();
+		output.setByteStream(outStream);
+		LSSerializer writer = impl.createLSSerializer();
+		writer.write(aPom, output);
+		return new String(outStream.toByteArray());
+	}
+
+	/**
+	 * @see #log
+	 */
+	public Log getLog()
+	{
+		return log;
+	}
+
+	/**
+	 * @see #log
+	 */
+	public void setLog(Log aLog)
+	{
+		log = aLog;
+	}
+
+}