Read project config from within the project

[kubukoz]

One of the original goals of the project was to allow every repository that uses pitgull to have a customizable config for it. Dhall was picked as the format, one of the reasons being that it supports remote imports.

With that in mind, the approximate setup could look like this: one would have a single repository with a shared config, and multiple other repositories could import from that, like in example.dhall:

let pg =
      https://raw.githubusercontent.com/pitgull/pitgull/v0.0.2/dhall/pitgull.dhall sha256:65a46e78c2d4aac7cd3afeb1fa209ed244dc60644634a9cfc61800ea3417ea9b

let wms =
      https://gitlab.com/kubukoz/demo/-/raw/db4686f29bab1bc056ec96307a39aa3dd6337173/wms.dhall sha256:4b9218b9a1a83262550b9bdfa7d7250f4aa365b8d8c2131f65517ef5f3eeb68c

in pg.projectToJson { rules = [ wms.scalaSteward ] }

Here, we have an import of the pitgull "standard library" and a shared config.

One obstacle here is authentication - to resolve the shared import, we might need to authenticate to the GitLab instance being used.

While we do have a token that should allow doing this, it is not clear whether we can make the dhall resolver (dhall-json in our case, until #116 is possible - in dhallj we could have a custom http4s client that will attach the header in the worst case) forward it in the appropriate header.

Note that we will need to fetch the base config file using the GitLab API - so we don't need to do anything more complex than the existing implementations of API calls do.

Hopefully, once we have that fetched (as a byte stream should be enough), we can pass it as input to dhall-json executed with the appropriate environment variable, which can then be forwarded with the using clause of an import: https://docs.dhall-lang.org/references/Built-in-types.html?highlight=headers#keyword-using