@mentions does not display the expected users and instead it displays less relevant users when a surname is short (i.e. two letters) and there are other users that have those letters somewhere as part of their username

Summary

The @mentions search does not display the relevant users, however it displays others that are less relevant to the specific search
when a surname is short (i.e. two letters) and there are other users that have those letters somewhere as part of their username. As the rest API call returns only 10 results sorted by user name it can happen that more relevant results will be filtered out due to sorting them by user name.

For example if I have the following 5 users with last name "Ha" that we can call "set A"

Ha Alex - username: alexha@example.com

Ha Charly – username: chha@example.com

Ha Daniel – username: daha@example.com

Ha James – username: jha@example.com

Ha Keiran – username: kha@example.com

and also have the following users with "ha" somewhere in the user name, that we can call "set B"

Haff Albert – username=aahaff@example.com

Hall Adrian – username=adhal@contractor.example.com

Haang Albert – username=ahaang@contractor.example.com

Habbs Alex – username=ahabbs@example.com

Habdd Anton – username=ahabdd@example.com

Haffman Alex – username=ahaffman@example.com

Halknar Ariel – username=ahalknar@example.com

Hams Albert – username=ahams@example.com

Hanga Alex – username=ahanga@example.com

Hax Anton – username=ahax@example.com

when issuing the @mentions as "@ha" the rest api call will return all the users in set B as it is sorted by user name, however for the end user is more relevant to find the users that have "ha" as surname which would appear on the list if the rest api call would return 15 users instead of the hardcoded value of 10. Then I believe that the algorithm that JIRA has to display the most relevant users would display those with Ha surname first, however we do not reach that point as the result set has only the users that do not have an Ha surname.

Obviously, the more users a customer would have to more likely they will find this problem.

Environment

• JIRA 7.2.6

Steps to Reproduce

1. Set up a JIRA 7.2.6 vanilla instance
2. Create the users detailed in the example above (both sets A and B)
3. Goto Comments in one issue and type @ha, then the user in set "B" will be displayed rather than the users in set "A"

Expected Results

The users that are most relevant to the @mentions search should be displayed

Actual Results

Users that are less relevant to the search are displayed.

Workaround

Changing the user name in a way that will be sorted before others will workaround the issue, however with a big number of users it is not possible to change each one to make it appear as it should.

Additional Comments

I believe the same problem would happen with short names, however for creating this bug only short surnames were tested.