That would require a commit to be localised to a block of code, and even atomic commits can be split across multiple files and modules. Plus, you would end up

That would require a commit to be localised to a block of code, and even atomic commits can be split across multiple files and modules. Plus, you would end up in a conflict between recording history and recording the present. What happens if you replace a complex method call across a codebase? The comments should explain the call, but the commit message needs to record how the call changed, and why - which you probably don't care about when coding.