in components/src/resources/resources.js [215:243]
async function loadReportsGroupingFilterFields(fetchYouTrack, projects) {
const fld = serializeArrayParameter('fld',
(projects || []).map(project => project.id)
);
const groupingFieldsTypes = [
'version[1]',
'ownedField[1]',
'state[1]',
'user[1]',
'enum[1]',
'build[1]',
'date',
'integer',
'float',
'period',
'project',
'string'
];
const fieldTypes = serializeArrayParameter('fieldTypes', groupingFieldsTypes);
const params = [
fld,
'$top=300',
`fields=${REPORT_FILTER_FIELDS_FIELDS}`,
fieldTypes,
'getUnusedVisibleFields=true'
].filter(param => param.length > 0).join('&');
return await fetchYouTrack(`api/filterFields?${params}`);
}