Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 18 Oct 2019 12:17:34 -0700 | Subject | Re: [GIT PULL] arm64: Fixes for -rc4 |
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On Fri, Oct 18, 2019 at 10:42 AM Will Deacon <will@kernel.org> wrote: > > Thanks, that's helpful to know for next time. I guess I'm most surprised by > the discrepancy between the shortlog and the diffstat, whereas I intuitively > expected them to be generated in the same way.
So logs and diffs are fundamentally different.
A log is an operation on a _set_ of commits (that's the whole point - you don't list the beginning and the end, you list all the commits in between), while a diff is fundamentally an operation on two end-points and shows the code difference between those two points.
And the summary versions of those operations (shortlog and diffstat) are no different.
So as a set operation, "shortlog" has no issues with multiple merge bases. Doing a shortlog is still just a set difference between your commits and the upstream commits, and the number of merge bases is irrelevant. "List all commits that I have, but upstream doesn't have" is a very straightforward and natural set operation.
But as a "two endpoints" operation, diffstat has real problems any time you have more than two endpoints - when you have multiple merge bases, you fundamentally have more than two endpoints: you have all of the merge bases, and then you have your end result.
What you doing the merge does is to turn the multiple merge bases into just one point: the thing you merged against now becomes the common merge point, and now you have a "two endpoints" for the diffstat: the thing you merged against, and your end result are now the two points that you can diff against.
But the shortlog is always correct, because it just doesn't even care about that whole issue.
Linus
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