[#3] start implementing comment formatting.

src/main/java/org/codehaus/mojo/tidy/task/EnsureCommentsOnSingleLine.java

@@ -0,0 +1,133 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.codehaus.mojo.tidy.task;
+
+import static org.codehaus.mojo.tidy.task.XMLEventReaderFactory.createEventReaderForPom;
+
+import javax.xml.stream.Location;
+import javax.xml.stream.XMLEventReader;
+import javax.xml.stream.XMLStreamException;
+import javax.xml.stream.events.XMLEvent;
+import java.util.Collections;
+
+public class EnsureCommentsOnSingleLine implements TidyTask
+{
+
+    @Override
+    public String tidyPom( String pom, Format format ) throws XMLStreamException
+    {
+        XMLEventReader eventReader = createEventReaderForPom( pom );
+        try
+        {
+            return moveTrailingComments( pom, eventReader, format );
+        }
+        finally
+        {
+            eventReader.close();
+        }
+    }
+
+    private String moveTrailingComments( String pom, XMLEventReader reader, Format format ) throws XMLStreamException
+    {
+        StringBuilder outputPom = new StringBuilder();
+        XMLEvent previousEvent = null;
+        int indent = 0;
+        int startPrevEl = 0;
+        int startCurrentEl;
+
+        while ( reader.hasNext() )
+        {
+            XMLEvent event = reader.nextEvent();
+            final Location location = event.getLocation();
+            startCurrentEl = location.getCharacterOffset();
+            switch ( event.getEventType() )
+            {
+                case XMLEvent.COMMENT:
+                    final int startOfNextElement = getPosOfNextEvent( reader );
+
+                    if ( previousElementInSameRow( location, previousEvent ))
+                    {
+                        final String whitespace = String.join( "", Collections.nCopies( indent, " " ) );
+                        final String textToInsert =
+                                pom.substring( startCurrentEl, startOfNextElement )
+                                        + format.getLineSeparator()
+                                        + whitespace;
+                        outputPom.insert( startPrevEl, textToInsert );
+                    }
+                    else
+                    {
+                        outputPom.append( pom, startCurrentEl, startOfNextElement );
+                    }
+
+                    break;
+
+                case XMLEvent.END_DOCUMENT:
+                    outputPom.append( pom.substring( startCurrentEl ) );
+                    break;
+
+                case XMLEvent.START_ELEMENT:
+                    startPrevEl = startCurrentEl;
+                    indent = location.getColumnNumber() - 1;
+                    // pass-through
+                default:
+                    final int next = getPosOfNextEvent( reader );
+                    previousEvent = event;
+
+                    outputPom.append( pom, startCurrentEl, next );
+                    break;
+            }
+        }
+
+        return outputPom.toString();
+    }
+
+    private boolean previousElementInSameRow( Location location, XMLEvent previousElement )
+    {
+        if ( previousElement == null )
+        {
+            return false;
+        }
+
+        return location.getLineNumber() == previousElement.getLocation().getLineNumber();
+    }
+
+    private boolean nextElementInSameRow( Location location, XMLEventReader reader ) throws XMLStreamException
+    {
+        final XMLEvent peek = reader.peek();
+
+        if ( peek == null )
+        {
+            return false;
+        }
+
+        if ( peek.getEventType() != XMLEvent.START_ELEMENT )
+        {
+            return false;
+        }
+
+        return peek.getLocation().getLineNumber() == location.getLineNumber();
+    }
+
+    private int getPosOfNextEvent( XMLEventReader reader )
+            throws XMLStreamException
+    {
+        return reader.peek().getLocation().getCharacterOffset();
+    }
+}

src/main/java/org/codehaus/mojo/tidy/task/PomTidy.java

@@ -32,7 +32,8 @@ public class PomTidy
     private static final FormatIdentifier FORMAT_IDENTIFIER = new FormatIdentifier();
 
     private static final List<TidyTask> TIDY_TASKS =
-        asList( new EnsureXmlHeader(), new EnsureOrderAndIndent(), new EnsureSingleLineProjectStartTag(),
+        asList( new EnsureXmlHeader(),
+                new EnsureCommentsOnSingleLine(), new EnsureOrderAndIndent(), new EnsureSingleLineProjectStartTag(),
                 new EnsureTrailingNewLine() );
 
     public String tidy( String pom )

src/test/java/org/codehaus/mojo/tidy/task/PomTidyTest.java

@@ -41,7 +41,7 @@ public static Iterable<String> tests()
         return asList( "add-xml-declaration", "complete-pom", "do-not-mix-tab-and-spaces", "groupid-artifactid-version",
                        "plugin-config-with-maven-element-names", "pom-space-indent", "pom-tab-indent",
                        "pom-with-comments", "pom-with-crlf", "pom-with-line-without-indent", "pom-with-profiles",
-                       "pom-with-reporting", "project-single-line" );
+                       "pom-with-reporting", "project-single-line", "TIDY-3_comment" );
     }
 
     @Parameter( 0 )

src/test/resources/org/codehaus/mojo/tidy/task/TIDY-3_comment/pom-expected.xml

@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.codehaus.mojo.tidy.its</groupId>
+  <artifactId>pom-space-indent</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <description>Test of tidy:pom on a pom with XML comments.</description>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <!-- bla bla 1 -->
+      <groupId>org.apache.httpcomponents</groupId>
+      <artifactId>httpclient</artifactId>
+      <version>4.5.2</version>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.integration</groupId>
+      <artifactId>spring-integration-java-dsl</artifactId>
+      <!-- bla bla 2 -->
+      <version>1.1.2.RELEASE</version>
+    </dependency>
+  </dependencies>
+</project>

src/test/resources/org/codehaus/mojo/tidy/task/TIDY-3_comment/pom.xml

@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.codehaus.mojo.tidy.its</groupId>
+  <artifactId>pom-space-indent</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <description>Test of tidy:pom on a pom with XML comments.</description>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <!-- bla bla 1 -->
+      <groupId>org.apache.httpcomponents</groupId>
+      <artifactId>httpclient</artifactId>
+      <version>4.5.2</version>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.integration</groupId>
+      <artifactId>spring-integration-java-dsl</artifactId>
+      <version>1.1.2.RELEASE</version> <!-- bla bla 2 -->
+    </dependency>
+  </dependencies>
+
+</project>