alt Hacker NewsMany changes require multiple smaller changes, so this is not always possible.
For me the commit message should tell me the what/why and the diff is the how. It's great to understand if, for example, a change was intentional or a bug.
Many times when searching for the source of a bug I could not tell if the line changed was intentional or a mistake because the commit message was simply repeating what was on the diff. If you say your intention was to add something and the diff shows a subtraction, you can easily tell it was a mistake. Contrived example but I think it demonstrates my point.
This only really works if commits are meaningful though. Most people are careless and half their commits are 'fix this', 'fix again', 'wip', etc. At that point the only place that can contain useful information on the intentions are the pull requests/issues around it.
Take a single commit from the Linux kernel: https://github.com/torvalds/linux/commit/08bd5b7c9a2401faabd... It doesn't tell me "add function X, Y and boolean flag Z". It tells us what/why it was done, and the diff shows us how.
I don't know when do you think I wrote that "the how" was needed because of course it's not needed. Again, OP wrote about just having "the why" in the message which is bad imho and you need "the what" there as well. As per your commit, the title is "fix crash when enabling pass-through port" which is exactly what I mean - it says what was done in a clear manner.