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The two most significant yet complex elements of Java generics are wildcards and type argument inference. Both processes rely on the compiler. Even though type argument inference and wildcard execution are implicit processes, a programmer should be aware of them to make the most of the features. A compiler error message tells much about the code and the process mechanism. If the error message is unambiguous and sound, it is easy for the programmer to debug the code. However, in the context of wildcard-type argument inference, the current Javac compiler emits cryptic and imprecise error messages. A programmer may get confused about the inference outcome and failure, so it will be difficult to resolve the errors easily. In this paper, we propose a few additions to the current Wildcard-based type inference algorithm to get detailed and valuable error messages. We implement a Java compiler plugin tool based on the proposed algorithm. The plugin can be easily executed through the Java command line. It gives a comprehensive error message that aids programmers in resolving errors more effectively.
