How does stack find packages from extra-deps?

Question

In https://docs.haskellstack.org/en/stable/GUIDE/#extra-deps

The docs mentioned one example of adding and extra-deps only by name. I know that we can specific GitHub url too, but when we provide just the name, how stack knows where to find a package that is not in the snapshot?

Answer 1

Ok, the blog post mentioned by @sjakobi says that both cabal-install and stack uses the package index from hackage.