This allows the git repository to be moved while git-annex is running in
it, with fewer problems.
On Windows, this avoids some of the problems with the absurdly small
MAX_PATH of 260 bytes. In particular, git-annex repositories should
work in deeper/longer directory structures than before. See
http://git-annex.branchable.com/bugs/__34__git-annex:_direct:_1_failed__34___on_Windows/
There are several possible ways this change could break git-annex:
1. If it changes its working directory while it's running, that would
be Bad News. Good news everyone! git-annex never does so. It would also
break thread safety, so all such things were stomped out long ago.
2. parentDir "." -> "" which is not a valid path. I had to fix one
instace of this, and I should probably wipe all calls to parentDir out
of the git-annex code base; it was never a good idea.
3. Things like relPathDirToFile require absolute input paths,
and code assumes that the git repo path is absolute and passes it to it
as-is. In the case of relPathDirToFile, I converted it to not make
this assumption.
Currently, the test suite has 16 failures.
It's ok to probe every time for git-branch remove because that's
run quite rarely. For git-checkattr, it's run only once, when
starting the --batch mode, and so again the overhead is pretty minimal.
This leaves 2 places where the build version is still used.
git merge might be interactive or fail if one skews, and --no-gpg-sign
might not be pased, or might be passed to a git that doesn't understand it
if the other skews. It seems a little expensive to check the git version
each time these are used.
This doesn't seem likely to cause many problems, at least compared with
check-attr hanging on skew.
I have not actually tested with 1.8.5, which is not yet relesaed, but
git.git commit f7cd8c50b9ab83e084e8f52653ecc8d90665eef2 changes -z
to also apply to output, without regards to back-compat. (But with pretty
good reasons.)
New code should work with both versions, by fingerprinting for NULs and
newlines.
Fuzz tests have shown that git cat-file --batch sometimes stops running.
It's not yet known why (no error message; repo seems ok). But this is
something we can deal with in the CoProcess framework, since all 3 types of
long-running git processes should be restartable if they fail.
Note that, as implemented, only IO errors are caught. So an error thrown
by the reveiver, when it sees something that is not valid output from
git cat-file (etc) will not cause a restart. I don't want it to retry
if git commands change their output or are just outputting garbage.
This does mean that if the command did a partial output and crashed in the
middle, it would still not be restarted.
There is currently no guard against restarting a command repeatedly, if,
for example, it crashes repeatedly on startup.
Now gitattributes are looked up, efficiently, in only the places that
really need them, using the same approach used for cat-file.
The old CheckAttr code seemed very fragile, in the way it streamed files
through git check-attr.
I actually found that cad8824852
was still deadlocking with ghc 7.4, at the end of adding a lot of files.
This should fix that problem, and avoid future ones.
The best part is that this removes withAttrFilesInGit and withNumCopies,
which were complicated Seek methods, as well as simplfying the types
for several other Seek methods that had a Backend tupled in.
Under ghc 7.4, this seems to be able to handle all filename encodings
again. Including filename encodings that do not match the LANG setting.
I think this will not work with earlier versions of ghc, it uses some ghc
internals.
Turns out that ghc 7.4 has a special filesystem encoding that it uses when
reading/writing filenames (as FilePaths). This encoding is documented
to allow "arbitrary undecodable bytes to be round-tripped through it".
So, to get FilePaths from eg, git ls-files, set the Handle that is reading
from git to use this encoding. Then things basically just work.
However, I have not found a way to make Text read using this encoding.
Text really does assume unicode. So I had to switch back to using String
when reading/writing data to git. Which is a pity, because it's some
percent slower, but at least it works.
Note that stdout and stderr also have to be set to this encoding, or
printing out filenames that contain undecodable bytes causes a crash.
IMHO this is a misfeature in ghc, that the user can pass you a filename,
which you can readFile, etc, but that default, putStr of filename may
cause a crash!
Git.CheckAttr gave me special trouble, because the filenames I got back
from git, after feeding them in, had further encoding breakage.
Rather than try to deal with that, I just zip up the input filenames
with the attributes. Which must be returned in the same order queried
for this to work.
Also of note is an apparent GHC bug I worked around in Git.CheckAttr. It
used to forkProcess and feed git from the child process. Unfortunatly,
after this forkProcess, accessing the `files` variable from the parent
returns []. Not the value that was passed into the function. This screams
of a bad bug, that's clobbering a variable, but for now I just avoid
forkProcess there to work around it. That forkProcess was itself only added
because of a ghc bug, #624389. I've confirmed that the test case for that
bug doesn't reproduce it with ghc 7.4. So that's ok, except for the new ghc
bug I have not isolated and reported. Why does this simple bit of code
magnet the ghc bugs? :)
Also, the symlink touching code is currently broken, when used on utf-8
filenames in a non-utf-8 locale, or probably on any filename containing
undecodable bytes, and I temporarily commented it out.
