Add checks to prevent cycling hierarchy (!9438) · Merge requests · GitLab.org / GitLab

What does this MR do?

It adds checks when adding an epic to a parent epic

if a given child epic is not the same as the parent epic
if a given child epic is not parent of the given parent epic or any other epic of the parent epic parents

Changelog entry added, if necessary
[-] Documentation created/updated via this MR
[-] Documentation reviewed by technical writer or follow-up review issue created
Tests added for this feature/bug
[-] Tested in all supported browsers
Conforms to the code review guidelines
Conforms to the merge request performance guidelines
Conforms to the style guides
[-] Conforms to the database guides
[-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
[-] EE specific content should be in the top level /ee folder
[-] For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
Security reports checked/validated by reviewer