Difftastic would not solve the issue described by madeofpalk because it still highlights the added comma. You need a diff tool that can distinguish between optional and required syntax. So far I am not aware of any tool that supports this, except the one I am working on (SemanticDiff).

But diff does not exists in a vacuum. It would need to be integrated to IDEs, editor, merge tools, PR tools. You now have to have `patch` understand and depend on the details of the syntax of your language. In a way that may break between different versions of diff and patch. Not even starting with variants of a language, different interpretations of how to handle the preprocessor/macros system, different editions of the same language.

All that, just to not have to add a trailing comma ?