At the moment, we are using JQL directly to fetch epic links for a given project. This is resulting in inconsistent behavior between Mattermost's epic selector and Jira's.
One known limitation to the current implementation is that the epic links must be a member of the same project as selected in the MM form. Jira's epic link selector allows for epics from other projects, so that functionality should be tested with this feature.
At the moment, we are using JQL directly to fetch epic links for a given project. This is resulting in inconsistent behavior between Mattermost's epic selector and Jira's.
https://github.com/mattermost/mattermost-plugin-jira/blob/17e8a47f8a644f853383301e6129ee940d715942/webapp/src/components/data_selectors/jira_epic_selector/jira_epic_selector.tsx#L79
We can instead use the autocomplete endpoint for a project's epic links: https://myorg.atlassian.net/rest/agile/1.0/epic/search?excludeDone=true&projectKey=CLD&maxResults=20&query=
One known limitation to the current implementation is that the epic links must be a member of the same project as selected in the MM form. Jira's epic link selector allows for epics from other projects, so that functionality should be tested with this feature.