Internally as Google, you have a substantially power powerful version of Codesearch, which is semantic, i.e. it relies on actual binary artifacts produced by builds to index code. All of the code base uses Blaze ( open sourced as Bazel) to express the rules.
The version of code search here is cute, but it's still not a full blown structured semantic code search, which I really miss. Searching for and browsing code on Github feels underwhelming in comparison, because you wan't really find or explore code the way you think of it.
You can see a demo of semantic Codesearch tech externalized here at:
https://blog.bazel.build/2017/12/14/introducing-bazel-code-s... http://cs.chromium.org
For example if you click on a header or a symbol, you can get proper cross references to a symbol.
https://cs.chromium.org/chromium/src/pdf/document_loader_imp...
I really wish they add structured code search to Cloud Repos, even if it comes with some heavy restrictions such you must use Bazel as a build system.
It would be a killer feature, and to my knowledge there is no equivalent to such a product. IDEs offer some similar overlapping functionality, though other code search engines still operate in terms of strings rather than actually real binary symbols ( I think Sourcegraph is trying here but that still does not seem to use some kind of accurate and structured information like you have in the code, it still seems not use build rules).