Groovy version 2.5 requires Java 7 and Groovy version 3 requires Java 8 whereas logback version 1.2 requires Java 6. Thus using Groovy 2.5 or later in logback 1.2 is not an option.

How about a version of logback 1.2.4 but without Groovy support? This version could be made available in Maven central without publicizing it. How does that sound?