Clover uses ANTLR 2.x currently which is few light-years from the latest version, which is ANTLR 4.x. Upgrade to the latest ANTLR library version.

• check ANTLR 4.x license (it's different from 2.x) whether we can actually use it; if not - try to use 3.x, if possible
• check if there's any Java grammar (the best for Java 8) available for Antlr 4
• estimate whether it's better to use completely new grammar file and embed clover stuff there or to upgrade our existing grammar file from 2.x to 4.x
  • watch out for our custom extensions like unicode escape sequence handling, annotations etc