Here's the dream; do a refactoring and submit patches for code review. The reviewers first ask "does this (unintentionally) change the behavior of the code?" They look at the semantic patch/run a semantic diff and see that it gives no output. So then they know that it is truly a refactoring and can review it as such without having to bother with any regression testing or anything like that.

Also, I want to have an option/convention to say that "this commit is best viewed with line-based diff/word-based diff, AST diff, semantic diff, ...".