My colleague, Chris, recently posted about what makes a good commit note. His main point is that a good commit note should explain why the changeset exists rather than what it contains (which should be more self-evident). I agree with this and (as Chris mentions) it’s of particular benefit when you have to do some software archeology. I’d go a step further and say that, for me, the best commit notes express the business reason for the changeset. If as a developer you are struggling to explain the business case for a particular change, (imho) you should try to find out before committing – otherwise how do you know the changeset is delivering value to the business?
In a previous post about preferring tests over comments, I expressed similar sentiments about using comments and tests to explain why rather than what. Chris’ post prompted me to re-read that old post and I noticed that it didn’t explain why I prefer tests over comments. The reason is that comments have a nasty habit of becoming out-of-date and getting left lying around to confuse the unwary, whereas you are forced to keep tests up-to-date (assuming they are part of a continuous integration build). For similar reasons I also think that commit notes are better than code comments, because they are forever associated with a snapshot of the code at the time they were written – leaving less scope for confusion.