backup: test that vss backups work if underlying data was removed

cmd/restic/cmd_backup.go

@@ -95,6 +95,7 @@ type BackupOptions struct {
 }
 
 var backupOptions BackupOptions
+var backupFSTestHook func(fs fs.FS) fs.FS
 
 // ErrInvalidSourceData is used to report an incomplete backup
 var ErrInvalidSourceData = errors.New("at least one source file could not be read")
@@ -598,6 +599,10 @@ func runBackup(ctx context.Context, opts BackupOptions, gopts GlobalOptions, ter
 		targets = []string{filename}
 	}
 
+	if backupFSTestHook != nil {
+		targetFS = backupFSTestHook(targetFS)
+	}
+
 	wg, wgCtx := errgroup.WithContext(ctx)
 	cancelCtx, cancel := context.WithCancel(wgCtx)
 	defer cancel()

cmd/restic/cmd_backup_integration_test.go

@@ -111,6 +111,53 @@ func TestBackupWithRelativePath(t *testing.T) {
 	rtest.Assert(t, latestSn.Parent != nil && latestSn.Parent.Equal(firstSnapshotID), "second snapshot selected unexpected parent %v instead of %v", latestSn.Parent, firstSnapshotID)
 }
 
+type vssDeleteOriginalFS struct {
+	fs.FS
+	testdata   string
+	hasRemoved bool
+}
+
+func (f *vssDeleteOriginalFS) Lstat(name string) (os.FileInfo, error) {
+	if !f.hasRemoved {
+		// call Lstat to trigger snapshot creation
+		_, _ = f.FS.Lstat(name)
+		// nuke testdata
+		if err := os.RemoveAll(f.testdata); err != nil {
+			return nil, err
+		}
+		f.hasRemoved = true
+	}
+	return f.FS.Lstat(name)
+}
+
+func TestBackupVSS(t *testing.T) {
+	if runtime.GOOS != "windows" || fs.HasSufficientPrivilegesForVSS() != nil {
+		t.Skip("vss fs test can only be run on windows with admin privileges")
+	}
+
+	env, cleanup := withTestEnvironment(t)
+	defer cleanup()
+
+	testSetupBackupData(t, env)
+	opts := BackupOptions{UseFsSnapshot: true}
+
+	var testFS *vssDeleteOriginalFS
+	backupFSTestHook = func(fs fs.FS) fs.FS {
+		testFS = &vssDeleteOriginalFS{
+			FS:       fs,
+			testdata: env.testdata,
+		}
+		return testFS
+	}
+	defer func() {
+		backupFSTestHook = nil
+	}()
+
+	testRunBackup(t, filepath.Dir(env.testdata), []string{"testdata"}, opts, env.gopts)
+	testListSnapshots(t, env.gopts, 1)
+	rtest.Equals(t, true, testFS.hasRemoved, "testdata was not removed")
+}
+
 func TestBackupParentSelection(t *testing.T) {
 	env, cleanup := withTestEnvironment(t)
 	defer cleanup()