62 lines
3.1 KiB
Text
62 lines
3.1 KiB
Text
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Yesterday I learned of a nasty bug in handling of merges in direct mode. It
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turns out that if the remote repository has added a file, and there is a
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conflicting file in the local work tree, which has not been added to git, the
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local file was overwritten when git-annex did a merge. That's really bad, I'm
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very unhappy this bug lurked undetected for so long.
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Understanding the bug was easy. Fixing it turned out to be hard, because
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the automatic merge conflict resolution code was quite a mess. In
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particular, it wrote files to the work tree, which made it difficult for a
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later stage to detect and handle the abovementioned case. Also, the
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automatic merge resolution code had weird asymetric structure that I never
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fully understood, and generally needed to be stared at for an hour to begin
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to understand it.
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In the process of cleaning that up, I wrote several more tests,
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to ensure that every case was handled correctly. Coverage was about 50%
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of the cases, and should now be 100%.
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To add to the fun, a while ago I had dealt with a bug on FAT/Windows where
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it sometimes lost the symlink bit during automatic merge resolution. Except
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it turned out my test case for it had a heisenbug, and I had not actually
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fixed it (I think). In any case, my old fix for it was a large part
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of the ugliness I was cleaning up, and had to be rewritten.
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Fully tracking down and dealing with that took a large part of today.
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Finally this evening, I added support for automatically handling merge
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conflicts where one side is an annexed file, and the other side has the
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same filename committed to git in the normal way. This is not an important
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case, but it's worth it for completeness. There was an unexpected benefit
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to doing it; it turned out that the weird asymetric part of the code went
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away.
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The final core of the automatic merge conflict resolver has morphed from
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a mess I'd not want to paste here to a quite consise and easy to follow
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bit of code.
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[[!format haskell """
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case (kus, kthem) of
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-- Both sides of conflict are annexed files
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(Just keyUs, Just keyThem) -> resolveby $
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if keyUs == keyThem
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then makelink keyUs
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else do
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makelink keyUs
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makelink keyThem
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-- Our side is annexed file, other side is not.
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(Just keyUs, Nothing) -> resolveby $ do
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graftin them file
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makelink keyUs
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-- Our side is not annexed file, other side is.
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(Nothing, Just keyThem) -> resolveby $ do
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graftin us file
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makelink keyThem
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-- Neither side is annexed file; cannot resolve.
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(Nothing, Nothing) -> return Nothing
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"""]]
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Since the bug that started all this is so bad, I want to make a release
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pretty soon.. But I will probably let it soak and whale on the test suite
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a bit more first. (This bug is also probably worth backporting to old
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versions of git-annex in eg Debian stable.)
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