You should look at Buck2. One of the coauthors of that paper (Neil) is one of the lead developers, and unlike Buck1 the buck2 binary exposes a very tiny API tha

You should look at Buck2. One of the coauthors of that paper (Neil) is one of the lead developers, and unlike Buck1 the buck2 binary exposes a very tiny API that consumers then build off of, and define all their rules, using Starlark for everything. This means that your build rules and your code exist together, as they should. And it recently started supporting the remote build API that Bazel does, so distributed builds and caching already work as they should. It's a very exciting project in the space.