This has been the ultimate goal for the pipeline for some time---the ability
to declaratively define the lowering pipeline in a way that is clear,
concise, and is correct by definition.
The reason that the lowering pipeline required so much boilerplate was
because of the robust types involved, which ensures that everything in the
pipeline is compatible with one-another---it's not possible to construct a
pipeline that will not work.
Of course, there is nuance involved in some cases---I didn't want to include
the `until` clause, which makes it fail the "obviously correct" criterion,
but that can be improved over time.
This only abstracts away `load_xmlo` and `parse_package_xml`; next I'll have
to evolve the abstraction to support lifetimes for `lower_xmli`'s
`AsgTreeToXirf`. That pipeline also ends with a custom sink that really
ought to become its own parser, but I don't want to jump down that rabbit
hole right now, so we may just support custom sinks for now with the intent
of removing it in the future.
This has been a long time coming. The ultimate goal is that you should be
able to look at the parser pipelines to have a clear, high-level overview of
how everything fits together. I'm not generating documentation yet, but
that'll help serve as a guide as well.
DEV-13162
Mike Gerwitz
9c6b00a124