I think you have to visit https://github.com/search https://github.com/search, type a query (use /.../ for a regex, and repo:... to filter by repo), then click

I think you have to visit https://github.com/search https://github.com/search, type a query (use /.../ for a regex, and repo:... to filter by repo), then click "Code" in the left navigation bar (and sign in). The search box on project pages appears to use the old search.