Is there any update on this?

Dave, any ETA?

There are two bugs remaining:

1. Things in the overlay repo aren't reachable if they're nested inside 1 or more directories that are *only* in the overlay repo.  For example https://cs-staging.chromium.org/chromium/infra/go/src/github.com/luci/luci-go/ - this exists in https://chromium.googlesource.com/infra/infra/codesearch/+/master/go/src/github.com/luci, but because the original repo only has "go/src", and is missing the "github.com/luci" directories, the gitlink resolution code that merges the directory hierarchies doesn't work.  Search still works though, and you can see search results from inside the directory: https://cs-staging.chromium.org/search/?q=f:infra/go/src/github.com/luci/luci-go&type=cs - so this is just an issue with the frontend flows.

2. x-refs from grok create links with URLs with an old-style "rcl=1481847532" query parameter.  Of course that's not a valid git revision, so the file isn't found when you click on it.  We need to teach grok about the real git revision that the index pack was generated from.

As a way to unblock other things, would it be possible to put this Git integration behind a flag to disable it in prod?

Update: I've fixed those two remaining bugs.  Unfortunately the request latency isn't quite as good now that the frontend is doing lots more requests to lookup gitlinks.  I have cl/144293661 to add a cache that brings performance back in line with the current codesearch.