Unfriendly user experience when you want to change your username, but it is already taken

Summary

Problem: I want to change my username, but it is already taken. However, I am not receiving any feedback from the system.

P.S. Sorry if this is a duplicate. I searched by labels and the key phrase “username change.”

Steps to reproduce

1. Open User settings -> Account
2. Try to change username that already taken

What is the current bug behavior?

No friendly feedback to the user.

What is the expected correct behavior?

Show the error below input, show toast, etc.

Relevant logs and/or screenshots

Request: PUT https://gitlab.com/-/profile/update_username.json

Input: {"user":{"username":"gwynplaine"}}

Output: {"message":"Username change failed - Username has already been taken"}

Output of checks

This bug happens on GitLab.com