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(stable) Restore the ":(attr:filter=lfs)" test for LFS

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Summary:
See D21190. The ".gitattributes" approach fails when ".gitattributes" is in a subdirectory (or global). These are probably unusual cases, but at least one is known in the wild.

Instead:

  - Restore the ":(attr:filter=lfs)" test, which seems to be the fastest accurate test available in modern Git.
  - If the test fails, assume the repository is not LFS. This only impacts users running very old versions of Git.

Test Plan:
  - In LFS and non-LFS repositories, created diffs. Saw correct detection again.
  - Broke the command on purpose, saw LFS detection conclude "no LFS", but not fail disastrously.

Subscribers: ptarjan

Differential Revision: https://secure.phabricator.com/D21192
This commit is contained in:
epriestley 2020-04-29 20:54:57 -07:00
parent f05ff65215
commit ce7bd67980
1 changed files with 48 additions and 15 deletions
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63
src/repository/api/ArcanistGitAPI.php
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@ -1679,31 +1679,64 @@ final class ArcanistGitAPI extends ArcanistRepositoryAPI {
}
public function isGitLFSWorkingCopy() {
// NOTE: This test previously used the command:
// We're going to run:
//
// $ git ls-files -z -- ':(attr:filter=lfs)'
//
// However, this does not work on old versions of Git (see PHI1718) and
// it potentially does a lot of unnecessary work when run in a large tree.
// ...and exit as soon as it generates any field terminated with a "\0".
//
// Instead, just check if ".gitattributes" exists and looks like it sets
// up an "lfs" filter for any pattern. This isn't completely accurate:
// If this command generates any such output, that means this working copy
// contains at least one LFS file, so it's an LFS working copy. If it
// exits with no error and no output, this is not an LFS working copy.
//
// - LFS can be configured with a global ".gitattributes" file, although
// this is unusual and discouraged by the official LFS documentation.
// - LFS may be configured only for files that don't actually exist in
// the repository.
//
// These cases are presumably very rare.
// If it exits with an error, we're in trouble.
$attributes_path = $this->getPath('.gitattributes');
if (!Filesystem::pathExists($attributes_path)) {
$future = $this->buildLocalFuture(
array(
'ls-files -z -- %s',
':(attr:filter=lfs)',
));
$lfs_list = id(new LinesOfALargeExecFuture($future))
->setDelimiter("\0");
try {
foreach ($lfs_list as $lfs_file) {
// We have our answer, so we can throw the subprocess away.
$future->resolveKill();
return true;
}
return false;
} catch (CommandException $ex) {
// This is probably an older version of Git. Continue below.
}
$attributes_data = Filesystem::readFile($attributes_path);
// In older versions of Git, the first command will fail with an error
// ("Invalid pathspec magic..."). See PHI1718.
//
// Some other tests we could use include:
//
// (1) Look for ".gitattributes" at the repository root. This approach is
// a rough approximation because ".gitattributes" may be global or in a
// subdirectory. See D21190.
//
// (2) Use "git check-attr" and pipe a bunch of files into it, roughly
// like this:
//
// $ git ls-files -z -- | git check-attr --stdin -z filter --
//
// However, the best version of this check I could come up with is fairly
// slow in even moderately large repositories (~200ms in a repository with
// 10K paths). See D21190.
//
// (3) Use "git lfs ls-files". This is even worse than piping "ls-files"
// to "check-attr" in PHP (~600ms in a repository with 10K paths).
//
// (4) Give up and just assume the repository isn't LFS. This is the
// current behavior.
return (bool)preg_match('(\bfilter\s*=\s*lfs\b)', $attributes_data);
return false;
}
}