fix: deleteVersions causing xl.meta to have empty Versions[] slice (#14483)

This is a side-affect of the optimization done in PR #13544 which
causes a certain type of delete operations on given object versions
can cause lastVersion indication to be skipped, which leads to
an `xl.meta` where Versions[] slice is empty while the entire
file is intact by itself.

This PR tries to ensure that such files are visible and deletable
by regular means of listing as null 'delete-marker' and also
avoid the situation where this potential issue might arise.

cmd/xl-storage-format-v2.go

@@ -1150,7 +1150,7 @@ func (x *xlMetaV2) sortByModTime() {
 // DeleteVersion deletes the version specified by version id.
 // returns to the caller which dataDir to delete, also
 // indicates if this is the last version.
-func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, bool, error) {
+func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, error) {
 	// This is a situation where versionId is explicitly
 	// specified as "null", as we do not save "null"
 	// string it is considered empty. But empty also
@@ -1164,7 +1164,7 @@ func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, bool, error) {
 	if fi.VersionID != "" {
 		uv, err = uuid.Parse(fi.VersionID)
 		if err != nil {
-			return "", false, errFileVersionNotFound
+			return "", errFileVersionNotFound
 		}
 	}
 
@@ -1179,7 +1179,7 @@ func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, bool, error) {
 			},
 		}
 		if !ventry.Valid() {
-			return "", false, errors.New("internal error: invalid version entry generated")
+			return "", errors.New("internal error: invalid version entry generated")
 		}
 	}
 	updateVersion := false
@@ -1225,18 +1225,18 @@ func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, bool, error) {
 		case LegacyType:
 			ver, err := x.getIdx(i)
 			if err != nil {
-				return "", false, err
+				return "", err
 			}
 			x.versions = append(x.versions[:i], x.versions[i+1:]...)
 			if fi.Deleted {
 				err = x.addVersion(ventry)
 			}
-			return ver.ObjectV1.DataDir, len(x.versions) == 0, err
+			return ver.ObjectV1.DataDir, err
 		case DeleteType:
 			if updateVersion {
 				ver, err := x.getIdx(i)
 				if err != nil {
-					return "", false, err
+					return "", err
 				}
 				if len(ver.DeleteMarker.MetaSys) == 0 {
 					ver.DeleteMarker.MetaSys = make(map[string][]byte)
@@ -1258,26 +1258,26 @@ func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, bool, error) {
 					ver.DeleteMarker.MetaSys[k] = []byte(v)
 				}
 				err = x.setIdx(i, *ver)
-				return "", len(x.versions) == 0, err
+				return "", err
 			}
 			var err error
 			x.versions = append(x.versions[:i], x.versions[i+1:]...)
 			if fi.MarkDeleted && (fi.VersionPurgeStatus().Empty() || (fi.VersionPurgeStatus() != Complete)) {
 				err = x.addVersion(ventry)
 			}
-			return "", len(x.versions) == 0, err
+			return "", err
 		case ObjectType:
 			if updateVersion && !fi.Deleted {
 				ver, err := x.getIdx(i)
 				if err != nil {
-					return "", false, err
+					return "", err
 				}
 				ver.ObjectV2.MetaSys[VersionPurgeStatusKey] = []byte(fi.ReplicationState.VersionPurgeStatusInternal)
 				for k, v := range fi.ReplicationState.ResetStatusesMap {
 					ver.ObjectV2.MetaSys[k] = []byte(v)
 				}
 				err = x.setIdx(i, *ver)
-				return "", len(x.versions) == 0, err
+				return "", err
 			}
 		}
 	}
@@ -1288,7 +1288,7 @@ func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, bool, error) {
 		}
 		ver, err := x.getIdx(i)
 		if err != nil {
-			return "", false, err
+			return "", err
 		}
 		switch {
 		case fi.ExpireRestored:
@@ -1314,16 +1314,16 @@ func (x *xlMetaV2) DeleteVersion(fi FileInfo) (string, bool, error) {
 		if x.SharedDataDirCount(ver.ObjectV2.VersionID, ver.ObjectV2.DataDir) > 0 {
 			// Found that another version references the same dataDir
 			// we shouldn't remove it, and only remove the version instead
-			return "", len(x.versions) == 0, nil
+			return "", nil
 		}
-		return uuid.UUID(ver.ObjectV2.DataDir).String(), len(x.versions) == 0, err
+		return uuid.UUID(ver.ObjectV2.DataDir).String(), err
 	}
 
 	if fi.Deleted {
 		err = x.addVersion(ventry)
-		return "", false, err
+		return "", err
 	}
-	return "", false, errFileVersionNotFound
+	return "", errFileVersionNotFound
 }
 
 // xlMetaDataDirDecoder is a shallow decoder for decoding object datadir only.