Why does auto-complete not work for GitHub mentions?

We join a number of different client projects throughout a year, and almost all of them use GitHub for source control and pull request reviews.

Recently, I ran into a weird issue with mentioning users in a pull request comment. The auto-complete feature was not working. I could type @ and then the first few letters of a username, but no suggestions would appear.

Even more odd, I could actually mention them if I typed out the name manually. So it wasn't blocking communication, but the extra friction was annoying.

After working with GitHub support (which was excellent, by the way), I learned that this has to do with how I was invited to the organization and how other people in the organization had their profile set.

To quote GitHub support:

The good news/bad news is that this is the expected behavior since you are a direct collaborator and not an organization member.

By default, a person's membership to an organization is private and only members of the same organization can see this membership. So unless you are added as an organization member, the autocomplete dropdown would only display other collaborators to you.

So there were two solutions:

1. The organization could add me as a member.
2. The people I was trying to mention could mark their organization membership as public.

We opted for the second solution, and now everything works as expected.

Here to help,

Joel

P.S. See how tenacious I am about figuring things out? Want some of that on your project?