HSEARCH-5394 Change how the "default" versions of the backends are set in the processor

so that we wouldn't need to update the version on each elasticsearch/lucene update

Author: marko-bekhta

metamodel/metamodel-processor/pom.xml

@@ -91,10 +91,27 @@
                 <artifactId>maven-surefire-plugin</artifactId>
                 <configuration>
                     <systemPropertyVariables>
-                        <org.hibernate.search.integrationtest.backend.elasticsearch.version>${version.org.elasticsearch.client}</org.hibernate.search.integrationtest.backend.elasticsearch.version>
+                        <org.hibernate.search.integrationtest.backend.elasticsearch.version>${version.org.elasticsearch.latest}</org.hibernate.search.integrationtest.backend.elasticsearch.version>
                     </systemPropertyVariables>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>org.jboss.maven.plugins</groupId>
+                <artifactId>maven-injection-plugin</artifactId>
+                <configuration>
+                    <bytecodeInjections>
+                        <bytecodeInjection>
+                            <expression>${version.org.elasticsearch.latest}</expression>
+                            <targetMembers>
+                                <methodBodyReturn>
+                                    <className>org.hibernate.search.processor.util.impl.DefaultBackendVersionUtils</className>
+                                    <methodName>latestElasticsearchVersion</methodName>
+                                </methodBodyReturn>
+                            </targetMembers>
+                        </bytecodeInjection>
+                    </bytecodeInjections>
+                </configuration>
+            </plugin>
         </plugins>
     </build>
     <profiles>

metamodel/metamodel-processor/src/main/java/org/hibernate/search/processor/HibernateSearchProcessorSettings.java

@@ -5,6 +5,9 @@
 package org.hibernate.search.processor;
 
 
+import static org.hibernate.search.processor.util.impl.DefaultBackendVersionUtils.latestElasticsearchVersion;
+import static org.hibernate.search.processor.util.impl.DefaultBackendVersionUtils.latestLuceneVersion;
+
 import java.io.Serializable;
 import java.time.Clock;
 import java.time.LocalDateTime;
@@ -80,11 +83,11 @@ public String formattedGeneratedAnnotation() {
 		}
 
 		public String elasticsearchVersion() {
-			return version == null ? "9.0.1" : version;
+			return version == null ? latestElasticsearchVersion() : version;
 		}
 
 		public String luceneVersion() {
-			return version == null ? "9.12.1" : version;
+			return version == null ? latestLuceneVersion() : version;
 		}
 
 		public String backendVersion() {

metamodel/metamodel-processor/src/main/java/org/hibernate/search/processor/util/impl/DefaultBackendVersionUtils.java

@@ -0,0 +1,32 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.processor.util.impl;
+
+import java.lang.reflect.Field;
+
+public final class DefaultBackendVersionUtils {
+	private DefaultBackendVersionUtils() {
+	}
+
+	public static String latestElasticsearchVersion() {
+		// This implementation is replaced during the build with another one that returns the correct value:
+		return "UNKNOWN";
+	}
+
+	public static String latestLuceneVersion() {
+		// since this one depends on which backend we pass to the processor ...
+		try {
+			Class<?> luceneVersionClass = Class.forName( "org.apache.lucene.util.Version" );
+			Field latestField = luceneVersionClass.getField( "LATEST" );
+
+			Object latestVersion = latestField.get( null );
+
+			return latestVersion.toString();
+		}
+		catch (ClassNotFoundException | NoSuchFieldException | IllegalAccessException e) {
+			return null;
+		}
+	}
+}