On Mon, Sep 23, 2013 at 02:37:29PM -0700, Jonathan Nieder wrote:
> Michael S. Tsirkin wrote:
> >> On Tue, Sep 17, 2013 at 04:56:16PM -0400, Jeff King wrote:
> >>>>> A problem with both schemes, though, is that they are not
> >>>>> backwards-compatible with existing git-patch-id implementations.
> >>> It may be esoteric enough not to worry about, though.
> Yeah, I think it would be okay. Details of the diff generation
> algorithm have changed from time to time anyway (and broken things,
> as you mentioned) and we make no guarantee about this.
> >> patch-id: make it more stable
> >> Add a new patch-id algorithm making it stable against
> >> hunk reodering:
> >> - prepend header to each hunk (if not there)
> >> - calculate SHA1 hash for each hunk separately
> >> - sum all hashes to get patch id
> >> Add --order-sensitive to get historical unstable behaviour.
> The --order-sensitive option seems confusing. How do I use it to
> replicate a historical patch-id?
You supply a historical diff to it :)
> If I record all options that might
> have influenced ordering (which are those?) then am I guaranteed to
> get a reproducible result?
Maybe not. But if you have a patch on disk, you will get
old hash from it with --order-sensitive.
> So I would prefer either of the following over the above:
> a) When asked to compute the patch-id of a seekable file, use the
> current streaming implementation until you notice a filename that
> is out of order. Then start over with sorted hunks (for example
> building a table of offsets within the patch for each hunk to
> support this).
> When asked to compute the patch-id of an unseekable file, stream
> to a temporary file under $GIT_DIR to get a seekable file.
This can be computed in one pass: just keep two checksums around.
But the result won't be stable: if you get same patch from two
people one is ordered, the other isn't, you get two different checksums.
What are we trying to achieve here?
> b) Unconditionally use the new patch-id definition that is stable
> under permutation of hunks. If and when someone complains that
> this invalidates their old patch-ids, they can work on adding a
> nice interface for getting the old-style patch-ids. I suspect it
> just wouldn't come up.
That's certainly easy to implement.
> Of course I can easily be wrong. Thanks for a clear patch that makes
> the choices easy to reasonable about.
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