Sourcegraph is a tool for
searching and navigating around large code bases.
The tool has various search
methods, including regular-expression search, and “structural search”,
which is
a relatively new technique that is language-aware.
The open-source core of
the tool comes
with code search, go-to-definition and other “code
intelligence” features, which provide ways for developers to make
sense of multi-repository code bases. Sourcegraph’s code-searching tools
can show documentation for
functions and methods on mouse hover and allow developers to
quickly jump to definitions or to find all references to a particular
identifier.

Source: LWN.net – [$] Searching code with Sourcegraph