Use Antrun plugin to eliminate javadoc version number in HTML

This is the one issue that cannot be solved regarding reproducible
builds by setting javadoc options, because that header comment is
hard-coded into the JDK with no option to avoid it. I just created an
OpenJDK issue (internal review ID 9076583, not published yet) for it,
but that does not help us today.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

aspectjmatcher/pom.xml

@@ -199,6 +199,19 @@
 				</executions>
 			</plugin>
 
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-antrun-plugin</artifactId>
+				<executions>
+					<!-- Remove javadoc version number from HTML comment to keep website diffs small -->
+					<execution>
+						<id>filter-javadocs</id>
+						<!-- Override default phase 'none' from parent -->
+						<phase>package</phase>
+					</execution>
+				</executions>
+			</plugin>
+
 			<!-- Caveat: Attaching the flattened POM needs packaging=jar, so do not use packaging=pom for this module -->
 			<plugin>
 				<groupId>org.codehaus.mojo</groupId>

aspectjrt/pom.xml

@@ -197,6 +197,19 @@
 				</executions>
 			</plugin>
 
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-antrun-plugin</artifactId>
+				<executions>
+					<!-- Remove javadoc version number from HTML comment to keep website diffs small -->
+					<execution>
+						<id>filter-javadocs</id>
+						<!-- Override default phase 'none' from parent -->
+						<phase>package</phase>
+					</execution>
+				</executions>
+			</plugin>
+
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-resources-plugin</artifactId>

aspectjtools/pom.xml

@@ -271,6 +271,19 @@
 				</executions>
 			</plugin>
 
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-antrun-plugin</artifactId>
+				<executions>
+					<!-- Remove javadoc version number from HTML comment to keep website diffs small -->
+					<execution>
+						<id>filter-javadocs</id>
+						<!-- Override default phase 'none' from parent -->
+						<phase>package</phase>
+					</execution>
+				</executions>
+			</plugin>
+
 			<!-- Caveat: Attaching the flattened POM needs packaging=jar, so do not use packaging=pom for this module -->
 			<plugin>
 				<groupId>org.codehaus.mojo</groupId>

aspectjweaver/pom.xml

@@ -272,6 +272,19 @@
 				</executions>
 			</plugin>
 
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-antrun-plugin</artifactId>
+				<executions>
+					<!-- Remove javadoc version number from HTML comment to keep website diffs small -->
+					<execution>
+						<id>filter-javadocs</id>
+						<!-- Override default phase 'none' from parent -->
+						<phase>package</phase>
+					</execution>
+				</executions>
+			</plugin>
+
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-resources-plugin</artifactId>

pom.xml

@@ -465,6 +465,45 @@
 						<windowtitle>${project.name} API</windowtitle>
 					</configuration>
 				</plugin>
+				<plugin>
+					<groupId>org.apache.maven.plugins</groupId>
+					<artifactId>maven-antrun-plugin</artifactId>
+					<version>3.1.0</version>
+					<executions>
+						<!--
+							Remove javadoc version number from HTML comment to keep website diffs small.
+
+							Attention: This has no effect on javadocs generated by the 'jar' goal, because they are archived while
+							Maven Javadoc runs, i.e. before this plugin execution kicks in. However, it cleans the javadocs before
+							Maven Resources copies them to aj-build/dist/docs/doc. I.e., they will be clean on the website, if copied
+							from that folder, and also in the installer.
+
+							TODO: In the future, maybe this execution or the whole Antrun plugin can go away, after a JDK feature
+							  request I just created (internal review ID 9076583) has been implemented and back-ported into all JDK
+							  versions we support for javadoc generation. But if that ever happens, it might take a while.
+						-->
+						<execution>
+							<id>filter-javadocs</id>
+							<!-- Override phase to 'package' in modules which need to filter javadocs -->
+							<phase>none</phase>
+							<goals>
+								<goal>run</goal>
+							</goals>
+							<configuration>
+								<target>
+									<!-- See https://ant.apache.org/manual/Tasks/replaceregexp.html -->
+									<replaceregexp byline="true">
+										<regexp pattern="^(&lt;!-- Generated by javadoc ).* (--&gt;)$"/>
+										<substitution expression="\1\2"/>
+										<fileset dir="${project.build.directory}/apidocs">
+											<include name="**/*.html"/>
+										</fileset>
+									</replaceregexp>
+								</target>
+							</configuration>
+						</execution>
+					</executions>
+				</plugin>
 				<plugin>
 					<groupId>org.asciidoctor</groupId>
 					<artifactId>asciidoctor-maven-plugin</artifactId>