project: migrate worktree .git/ dirs to symlinksv2.19

Historically we created a .git/ subdir in each source checkout and
symlinked individual files to the .repo/projects/ paths.  This layer
of indirection isn't actually needed: the .repo/projects/ paths are
guaranteed to only ever have a 1-to-1 mapping with the actual git
checkout.  So we don't need to worry about having files in .git/ be
isolated.

To that end, change how we manage the actual project checkouts from
a dir full of symlinks (and a few files) to a symlink to the internal
.repo/projects/ dir.  This makes the code simpler & faster.

The directory structure we have today is:
.repo/
  project-objects/chromiumos/third_party/kernel.git/
    <paths omitted as not relevant to this change>
  projects/src/third_party/kernel/
    v3.8.git/
      config
      description   -> …/project-objects/…/config
      FETCH_HEAD
      HEAD
      hooks/        -> …/project-objects/…/hooks/
      info/         -> …/project-objects/…/info/
      logs/
      objects/      -> …/project-objects/…/objects/
      packed-refs
      refs/
      rr-cache/     -> …/project-objects/…/rr-cache/
src/third_party/kernel/
  v3.8/
    .git/
      config        -> …/projects/…/v3.8.git/config
      description   -> …/project-objects/…/v3.8.git/description
      HEAD
      hooks/        -> …/project-objects/…/v3.8.git/hooks/
      index
      info/         -> …/project-objects/…/v3.8.git/info/
      logs/         -> …/projects/…/v3.8.git/logs/
      objects/      -> …/project-objects/…/v3.8.git/objects/
      packed-refs   -> …/projects/…/v3.8.git/packed-refs
      refs/         -> …/projects/…/v3.8.git/refs/
      rr-cache/     -> …/project-objects/…/v3.8.git/rr-cache/

The directory structure we have after this commit:
.repo/
  <nothing changes>
src/third_party/kernel/
  v3.8/
    .git            -> …/projects/…/v3.8.git

Bug: https://crbug.com/gerrit/15273
Change-Id: I9dd8def23fbfb2f4cb209a93f8b1b2b24002a444
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/323695
Reviewed-by: Mike Nichols <mikenichols@google.com>
Reviewed-by: Xin Li <delphij@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/tests/test_project.py b/tests/test_project.py
index 9b2cc4e9..d578fe84 100644
--- a/tests/test_project.py
+++ b/tests/test_project.py
@@ -16,6 +16,7 @@
 
 import contextlib
 import os
+from pathlib import Path
 import shutil
 import subprocess
 import tempfile
@@ -335,3 +336,52 @@ class LinkFile(CopyLinkTestCase):
     platform_utils.symlink(self.tempdir, dest)
     lf._Link()
     self.assertEqual(os.path.join('git-project', 'foo.txt'), os.readlink(dest))
+
+
+class MigrateWorkTreeTests(unittest.TestCase):
+  """Check _MigrateOldWorkTreeGitDir handling."""
+
+  _SYMLINKS = {
+      'config', 'description', 'hooks', 'info', 'logs', 'objects',
+      'packed-refs', 'refs', 'rr-cache', 'shallow', 'svn',
+  }
+  _FILES = {
+      'COMMIT_EDITMSG', 'FETCH_HEAD', 'HEAD', 'index', 'ORIG_HEAD',
+  }
+
+  @classmethod
+  @contextlib.contextmanager
+  def _simple_layout(cls):
+    """Create a simple repo client checkout to test against."""
+    with tempfile.TemporaryDirectory() as tempdir:
+      tempdir = Path(tempdir)
+
+      gitdir = tempdir / '.repo/projects/src/test.git'
+      gitdir.mkdir(parents=True)
+      cmd = ['git', 'init', '--bare', str(gitdir)]
+      subprocess.check_call(cmd)
+
+      dotgit = tempdir / 'src/test/.git'
+      dotgit.mkdir(parents=True)
+      for name in cls._SYMLINKS:
+        (dotgit / name).symlink_to(f'../../../.repo/projects/src/test.git/{name}')
+      for name in cls._FILES:
+        (dotgit / name).write_text(name)
+
+      subprocess.run(['tree', '-a', str(dotgit)])
+      yield tempdir
+
+  def test_standard(self):
+    """Migrate a standard checkout that we expect."""
+    with self._simple_layout() as tempdir:
+      dotgit = tempdir / 'src/test/.git'
+      project.Project._MigrateOldWorkTreeGitDir(str(dotgit))
+
+      # Make sure the dir was transformed into a symlink.
+      self.assertTrue(dotgit.is_symlink())
+      self.assertEqual(str(dotgit.readlink()), '../../.repo/projects/src/test.git')
+
+      # Make sure files were moved over.
+      gitdir = tempdir / '.repo/projects/src/test.git'
+      for name in self._FILES:
+        self.assertEqual(name, (gitdir / name).read_text())