Work around diffplug/spotless#834

gradle.properties

@@ -12,7 +12,13 @@ vintageVersion  = 5.8.0-SNAPSHOT
 defaultBuiltBy  = JUnit Team
 
 # We need more metaspace due to apparent memory leak in Asciidoctor/JRuby
-org.gradle.jvmargs=-Xmx1g -XX:MaxMetaspaceSize=512m -XX:+HeapDumpOnOutOfMemoryError
+# The exports are needed due to https://github.com/diffplug/spotless/issues/834
+org.gradle.jvmargs=-Xmx1g -XX:MaxMetaspaceSize=512m -XX:+HeapDumpOnOutOfMemoryError \
+  --add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \
+  --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \
+  --add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \
+  --add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \
+  --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
 org.gradle.caching=true
 org.gradle.parallel=true
 org.gradle.java.installations.fromEnv=JDK8,JDK16,JDK17