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Download and unzip: http://openide.netbeans.org/issues/showattachment.cgi?attach_id=8539 change the path to lexer module and type ant ant the DiffScanner*java files are generated again even there is no change in the input files. This confuses the rest of the ant script (compilation runs again) and should be fixed. Btw. why you do not write your own ant task instead of invoking main methods in your module jar?
I've added timestamp checking into the build script so now both Antlr and JavaCC should only be invoked if grammar file changes.