We took the phrase 'modern compiler' from the Ant project. A modern compiler is a JDK which does not have a tools.jar, but has the tools.jar classes in standard libraries (e.g. Mac OS X). In the earlier releases Gradle has checked whether a class from tools.jar is in the classpath. If so it was a 'modern compiler' and nothing had to be done, otherwise the tools.jar was added. We removed this behavior from he bootstrap code. But at a later lifecycle phase we still check if the classes from tools.jar are in the classpath, otherwise we add tools.jar. But we don't use the confusing 'modern compiler' phrase any longer. And the message only turns up in debug mode.