Sourcegraph has the best find-definition, find-references, and intelligent code navigation capability on the planet - and they brought it to GitLab.
With the GitLab native code intelligence integration from Sourcegraph, you can bring IDE-like features such as hover tooltips and go to definition to every GitLab code view. The below screencasts show you how to enable the Sourcegraph integration for both GitLab CE/EE and GitLab.com.
This screencast (with accompanying audio) shows how to enable and configure the Sourcegraph integration to bring code intelligence to all code views for public, private, and internal repositories on GitLab CE/EE instances.
This screencast (with accompanying audio) shows how to enable code intelligence for public repositories on GitLab.com.