javac currently emits MethodParameters attributes if -parameters is enabled even when writing v51 and earlier class files. It reports a warning when subsequently reading those class files if -Xlint:classfile is enabled.

original compiler-dev report:
http://mail.openjdk.java.net/pipermail/compiler-dev/2016-November/010508.html

The suggestion in the thread is to not emit the attributes when writing class file versions for which it is not appropriate.

=== X.java
class X {
  void f(int a) {}
}
=== Y.java
class Y {
  X x;
}
===

Repro (using 9.0.1+11):

$ javac -parameters -source 7 -target 7 X.java
$ javac -Xlint:classfile -sourcepath : Y.java
./X.class: warning: [classfile] MethodParameters attribute introduced in version 52.0 class files is ignored in version 51.0 class files