Attached is a test case from Robert Scholte that demonstrates a potential issue with javac when there are automatic modules on the module path.

$ javac -mp ./target/lib/-d mods/maven.settings.builder `find src -name "*.java"`
checking maven/builder/support/module-info
checking maven/settings/module-info
src/main/java/org/apache/maven/settings/io/DefaultSettingsReader.java:71: error: cannot access XmlPullParser
            return r.read( input, isStrict( options ) );
                    ^
  class file for org.codehaus.plexus.util.xml.pull.XmlPullParser not found
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
1 error