Manual changes to merge #4090 into master

Author: cowtowncoder

pom.xml

@@ -408,7 +408,60 @@
         </plugins>
       </build>
     </profile>
-
+    <profile>
+      <!-- And different set up for JDK 21 -->
+      <id>java21</id>
+      <activation>
+        <jdk>21</jdk>
+      </activation>
+      <build>
+        <plugins>
+          <plugin>
+            <groupId>org.codehaus.mojo</groupId>
+            <artifactId>build-helper-maven-plugin</artifactId>
+            <executions>
+              <execution>
+                <id>add-test-source</id>
+                <phase>generate-test-sources</phase>
+                <goals>
+                  <goal>add-test-source</goal>
+                </goals>
+                <configuration>
+                  <sources>
+                    <source>src/test-jdk14/java</source>
+                    <source>src/test-jdk17/java</source>
+                    <source>src/test-jdk21/java</source>
+                  </sources>
+                </configuration>
+              </execution>
+            </executions>
+          </plugin>
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <inherited>true</inherited>
+            <configuration>
+              <!-- Enable Java 21 for all sources so that Intellij picks the right language level -->
+              <source>21</source>
+              <release>21</release>
+              <compilerArgs>
+                <arg>-parameters</arg>
+                <arg>--add-opens=java.base/java.lang=ALL-UNNAMED</arg>
+                <arg>--add-opens=java.base/java.util=ALL-UNNAMED</arg>
+              </compilerArgs>
+            </configuration>
+          </plugin>
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-surefire-plugin</artifactId>
+            <configuration>
+              <argLine>--add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED</argLine>
+            </configuration>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
+ 
     <!-- 10-Nov-2020, tatu: Added via [databind#2931] -->
     <profile>
       <id>errorprone</id>