Add HTML artifact comparator

HTML documents can differ in textual representation but equal
semantically.

This adds a very basic support for semantic compare of html documents as
a first step it supports ignoring  script/css changes between different
java versions in the javadoc output.

tycho-artifactcomparator/pom.xml

@@ -77,6 +77,11 @@
 			<artifactId>java-diff-utils</artifactId>
 			<version>4.12</version>
 		</dependency>
+		<dependency>
+		    <groupId>ch.digitalfondue.jfiveparse</groupId>
+		    <artifactId>jfiveparse</artifactId>
+		    <version>1.0.1</version>
+		</dependency>
 	</dependencies>
 	<build>
 		<plugins>

tycho-artifactcomparator/src/main/java/org/eclipse/tycho/zipcomparator/internal/HtmlComparator.java

@@ -0,0 +1,110 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Christoph Läubrich and others.
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Christoph Läubrich - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.tycho.zipcomparator.internal;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+import org.codehaus.plexus.component.annotations.Component;
+import org.eclipse.tycho.artifactcomparator.ArtifactComparator.ComparisonData;
+import org.eclipse.tycho.artifactcomparator.ArtifactDelta;
+import org.eclipse.tycho.artifactcomparator.ComparatorInputStream;
+
+import ch.digitalfondue.jfiveparse.Comment;
+import ch.digitalfondue.jfiveparse.Document;
+import ch.digitalfondue.jfiveparse.Element;
+import ch.digitalfondue.jfiveparse.JFiveParse;
+import ch.digitalfondue.jfiveparse.Node;
+
+/**
+ * Compares html files for some special cases and fall back to simple textcompare otherwise
+ */
+@Component(role = ContentsComparator.class, hint = HtmlComparator.HINT)
+public class HtmlComparator implements ContentsComparator {
+
+    private static final String META_ELEMENT = "meta";
+    private static final String LINK_ELEMENT = "link";
+    private static final String SCRIPT_ELEMENT = "script";
+    private static final String HEAD_ELEMENT = "head";
+    static final String HINT = "html";
+
+    @Override
+    public ArtifactDelta getDelta(ComparatorInputStream baseline, ComparatorInputStream reactor, ComparisonData data)
+            throws IOException {
+        try {
+            Document baselineDoc = JFiveParse.parse(baseline.asString(StandardCharsets.UTF_8));
+            Document reactorDoc = JFiveParse.parse(reactor.asString(StandardCharsets.UTF_8));
+            //TODO we might generally want to remove all comment tags?
+            if (isJavadocHtml(baselineDoc)) {
+                cleanJavaDoc(baselineDoc.getDocumentElement());
+                cleanJavaDoc(reactorDoc.getDocumentElement());
+                String serializeBaseline = serializeAndNormalize(baselineDoc);
+                String serializeReactor = serializeAndNormalize(reactorDoc);
+                if (serializeBaseline.equalsIgnoreCase(serializeReactor)) {
+                    return ArtifactDelta.NO_DIFFERENCE;
+                }
+            } else {
+                //TODO compare each element and attributes ...
+            }
+        } catch (Exception e) {
+            //it might not be a valid html5 so don't bother and compare the text directly
+        }
+        return TextComparator.compareText(baseline, reactor, data);
+    }
+
+    private String serializeAndNormalize(Document baselineDoc) {
+        return JFiveParse.serialize(baselineDoc).replaceAll("\\s+", " ").replace("\r", "").replace("\n", "")
+                .replace("> <", "><");
+    }
+
+    private void cleanJavaDoc(Element root) {
+        //for javadoc we want to ignore all script and css tags...
+        for (Element headElement : root.getElementsByTagName(HEAD_ELEMENT)) {
+            for (Node node : headElement.getChildNodes().toArray(Node[]::new)) {
+                if (node instanceof Element element) {
+                    String nodeName = element.getNodeName();
+                    if (SCRIPT_ELEMENT.equalsIgnoreCase(nodeName) || LINK_ELEMENT.equalsIgnoreCase(nodeName)
+                            || META_ELEMENT.equals(nodeName)) {
+                        headElement.removeChild(node);
+                    }
+                }
+                if (node instanceof Comment comment) {
+                    headElement.removeChild(node);
+                }
+            }
+        }
+        //don't bother about lang...
+        root.removeAttribute("lang");
+    }
+
+    private boolean isJavadocHtml(Document doc) {
+        List<Element> elementsByTagName = doc.getDocumentElement().getElementsByTagName(HEAD_ELEMENT);
+        for (Element element : elementsByTagName) {
+            for (Node node : element.getChildNodes()) {
+                if (node instanceof Comment comment) {
+                    String data = comment.getData();
+                    if (data != null && data.trim().toLowerCase().startsWith("generated by javadoc")) {
+                        return true;
+                    }
+                }
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public boolean matches(String nameOrExtension) {
+        return HINT.equalsIgnoreCase(nameOrExtension) || "htm".equalsIgnoreCase(nameOrExtension);
+    }
+}