gc: add --keep-manifest-projects

By default, `repo gc` treats projects excluded by the configured
manifest groups as unused. This matches the active project set, but it
can remove cached Git data for projects that might be used again after
changing groups.

Add `--keep-manifest-projects` to keep Git data for projects that are
still in the manifests, even if the current groups exclude them or their
checkout is missing. Git data for projects no longer in the manifests
can still be removed.

Change-Id: I63ae18ce1c6acc2463be86f81921476b12fb27d7
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/629741
Reviewed-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Victor Pushkarev <corvinus.v@gmail.com>
Commit-Queue: Victor Pushkarev <corvinus.v@gmail.com>

tests/test_subcmds_gc.py

@@ -14,9 +14,11 @@
 
 """Unittests for the subcmds/gc.py module."""
 
+from pathlib import Path
 import unittest
 from unittest import mock
 
+import manifest_xml
 from subcmds import gc
 
 
@@ -80,3 +82,108 @@ class GcCommand(unittest.TestCase):
         ret = self.cmd.Execute(self.opt, [])
         self.assertEqual(ret, 1)
         self.mock_repack.assert_not_called()
+
+
+def test_gc_keep_manifest_projects(tmp_path: Path) -> None:
+    """Keep inactive projects that are still in the manifest."""
+    repodir = tmp_path / ".repo"
+    manifest_dir = repodir / "manifests"
+    manifest_file = repodir / manifest_xml.MANIFEST_FILE_NAME
+
+    repodir.mkdir()
+    manifest_dir.mkdir()
+
+    manifest_gitdir = repodir / "manifests.git"
+    manifest_gitdir.mkdir()
+    (manifest_gitdir / "config").write_text(
+        """[remote "origin"]
+        url = https://localhost:0/manifest
+        """,
+        encoding="utf-8",
+    )
+
+    manifest_file.write_text(
+        """\
+        <manifest>
+        <remote name="origin" fetch="http://localhost" />
+        <default remote="origin" revision="refs/heads/main" />
+        <project name="included" groups="active-group" />
+        <project name="excluded" groups="other-group" />
+        </manifest>
+        """,
+        encoding="utf-8",
+    )
+
+    manifest = manifest_xml.XmlManifest(str(repodir), str(manifest_file))
+    manifest.manifestProject.config.SetString(
+        "manifest.groups",
+        "active-group",
+    )
+
+    projects = {project.name: project for project in manifest.projects}
+    included = projects["included"]
+    excluded = projects["excluded"]
+
+    Path(included.gitdir).mkdir(parents=True)
+    Path(included.objdir).mkdir(parents=True)
+
+    # Simulate an inactive project with only its object cache left.
+    Path(excluded.objdir).mkdir(parents=True)
+    assert not excluded.Exists
+
+    orphan_gitdir = repodir / "projects" / "orphan.git"
+    orphan_objdir = repodir / "project-objects" / "orphan.git"
+    orphan_gitdir.mkdir()
+    orphan_objdir.mkdir()
+
+    cmd = gc.Gc(repodir=str(repodir), manifest=manifest)
+
+    opt, args = cmd.OptionParser.parse_args(
+        ["--yes", "--keep-manifest-projects"]
+    )
+    opt.quiet = True
+
+    selected_projects = cmd.GetProjects([], all_manifests=True)
+    assert included in selected_projects
+    assert excluded not in selected_projects
+
+    cmd.Execute(opt, args)
+
+    assert included.Exists
+    assert Path(excluded.objdir).exists()
+    assert not orphan_gitdir.exists()
+    assert not orphan_objdir.exists()
+
+
+def test_gc_keep_manifest_projects_preserves_repack_targets() -> None:
+    """Keep manifest projects without expanding repack targets."""
+    cmd = gc.Gc()
+    opt, _ = cmd.OptionParser.parse_args(
+        ["--keep-manifest-projects", "--repack"]
+    )
+    opt.this_manifest_only = False
+
+    with mock.patch.object(
+        cmd,
+        "GetProjects",
+        side_effect=[["projA"], ["manifest_projects"]],
+    ) as get_projects, mock.patch.object(
+        cmd, "delete_unused_projects", return_value=0
+    ) as delete, mock.patch.object(
+        cmd, "repack_projects", return_value=0
+    ) as repack:
+        cmd.Execute(opt, ["projA"])
+
+    get_projects.assert_has_calls(
+        [
+            mock.call(["projA"], all_manifests=True),
+            mock.call(
+                [],
+                groups="all",
+                missing_ok=True,
+                all_manifests=True,
+            ),
+        ]
+    )
+    delete.assert_called_once_with(["manifest_projects"], opt)
+    repack.assert_called_once_with(["projA"], opt)