public static IndexFormatVersion getVersion(IndexReader indexReader) {
FieldInfos fields = ReaderUtil.getMergedFieldInfos(indexReader);
if ((fields.fieldInfo(FieldNames.INDEX) != null && fields.fieldInfo(FieldNames.PATH) != null)
|| indexReader.numDocs() == 0) {
return IndexFormatVersion.V4;
} else if (fields.fieldInfo(FieldNames.LOCAL_NAME) != null) {
return IndexFormatVersion.V3;
} else if (fields.fieldInfo(FieldNames.PROPERTIES_SET) != null) {
return IndexFormatVersion.V2;
} else {
return IndexFormatVersion.V1;