MethodSymbol.params() generates parameter names if the symbols' params field has not been set externally. Currently an index variable [1] is never incremented, so the names will always be arg0 (instead of arg0, arg1, ...).

The bug was introduced in http://hg.openjdk.java.net/jdk/jdk/rev/89f6aa26fd6c.

This doesn't appear to be a regression, since that code path is only taken for synthetic methods. Synthetic methods aren't visible to annotation processors, and their parameter names don't end up in bytecode, so I don't think it's possible to observe the incorrect names.