members/all seems miss some inherited member

Summary

API endpoint /projects/ID/members/all does not list members of all ancestor groups.

Steps to reproduce

Consider the following setup:

• Groups: G1, G2
• Project: P1
• Users: U1, U2

With the following relationships

• Group G1 is "member" of P1
• Group G2 is "member" of G1
• User U1 is member of P1, U2 member of G2

Results in

• Request /projects/P1/members/all will return only U1.

Example Project

• P1: https://gitlab.com/ziyi.zhou/test-member-inheritance-p3
• G1: https://gitlab.com/test-member-inheritance-g1
• G2: https://gitlab.com/test-member-inheritance-g2

What is the current bug behavior?

• Request /projects/P1/members/all will return only U1.

What is the expected correct behavior?

• Request /projects/P1/members/all should return U1, U2(by U2 -> G2 -> G1 -> P1)

Output of checks

This bug happens on GitLab.com