project: support reftable anchors in worktree .git migration

The reftable backend creates real refs/ and reftable/ dirs. Update
_MigrateOldWorkTreeGitDir to expect these dirs and remove them.

Bug: 476209856
Change-Id: I4700da70cb466e25ecbc51ba4de9a906b8716bd8
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/550761
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

project.py

@@ -3632,14 +3632,20 @@ class Project:
         here.  The path updates will happen independently.
         """
         # Figure out where in .repo/projects/ it's pointing to.
-        if not os.path.islink(os.path.join(dotgit, "refs")):
+        gitdir = None
+        for name in ("refs", "reftable", "objects"):
+            path = os.path.join(dotgit, name)
+            if os.path.islink(path):
+                gitdir = os.path.dirname(os.path.realpath(path))
+                break
+        else:
             raise GitError(
                 f"{dotgit}: unsupported checkout state", project=project
             )
-        gitdir = os.path.dirname(os.path.realpath(os.path.join(dotgit, "refs")))
 
         # Remove known symlink paths that exist in .repo/projects/.
         KNOWN_LINKS = {
+            # go/keep-sorted start
             "config",
             "description",
             "hooks",
@@ -3648,9 +3654,11 @@ class Project:
             "objects",
             "packed-refs",
             "refs",
+            "reftable",
             "rr-cache",
             "shallow",
             "svn",
+            # go/keep-sorted end
         }
         # Paths that we know will be in both, but are safe to clobber in
         # .repo/projects/.
@@ -3675,7 +3683,16 @@ class Project:
             dotgit_path = os.path.join(dotgit, name)
             if name in KNOWN_LINKS:
                 if not platform_utils.islink(dotgit_path):
-                    unknown_paths.append(f"{dotgit_path}: should be a symlink")
+                    # In reftable format, refs and reftable can be directories.
+                    if name in ("refs", "reftable") and platform_utils.isdir(
+                        dotgit_path
+                    ):
+                        pass
+                    else:
+                        unknown_paths.append(
+                            f"{dotgit_path}: should be a symlink"
+                        )
+
             else:
                 gitdir_path = os.path.join(gitdir, name)
                 if name not in SAFE_TO_CLOBBER and os.path.exists(gitdir_path):
@@ -3697,6 +3714,13 @@ class Project:
             if name.endswith("~") or (name[0] == "#" and name[-1] == "#"):
                 platform_utils.remove(dotgit_path)
             elif name in KNOWN_LINKS:
+                if (
+                    name in ("refs", "reftable")
+                    and platform_utils.isdir(dotgit_path)
+                    and not platform_utils.islink(dotgit_path)
+                ):
+                    platform_utils.rmtree(dotgit_path)
+                else:
                     platform_utils.remove(dotgit_path)
             else:
                 gitdir_path = os.path.join(gitdir, name)

tests/test_project.py

@@ -341,6 +341,7 @@ class MigrateWorkTreeTests(unittest.TestCase):
     """Check _MigrateOldWorkTreeGitDir handling."""
 
     _SYMLINKS = {
+        # go/keep-sorted start
         "config",
         "description",
         "hooks",
@@ -349,9 +350,11 @@ class MigrateWorkTreeTests(unittest.TestCase):
         "objects",
         "packed-refs",
         "refs",
+        "reftable",
         "rr-cache",
         "shallow",
         "svn",
+        # go/keep-sorted end
     }
     _FILES = {
         "COMMIT_EDITMSG",
@@ -430,6 +433,25 @@ class MigrateWorkTreeTests(unittest.TestCase):
             for name in self._SYMLINKS:
                 self.assertTrue((dotgit / name).is_symlink())
 
+    def test_reftable_anchor_with_refs_dir(self):
+        """Migrate when reftable/ and refs/ are directories."""
+        with self._simple_layout() as tempdir:
+            dotgit = tempdir / "src/test/.git"
+            (dotgit / "refs").unlink()
+            (dotgit / "refs").mkdir()
+            (dotgit / "refs" / "heads").write_text("dummy")
+
+            (dotgit / "reftable").unlink()
+            (dotgit / "reftable").mkdir()
+            (dotgit / "reftable" / "tables.list").write_text("dummy")
+            project.Project._MigrateOldWorkTreeGitDir(str(dotgit))
+
+            self.assertTrue(dotgit.is_symlink())
+            self.assertEqual(
+                os.readlink(dotgit),
+                os.path.normpath("../../.repo/projects/src/test.git"),
+            )
+
 
 class ManifestPropertiesFetchedCorrectly(unittest.TestCase):
     """Ensure properties are fetched properly."""