What could make this Setup.hs use case less heavyweight?

*I was asked on #haskell to report this use case of a custom `Setup.hs` because apparently the Cabal developers would like to minimize such cases. My personal opinion is that my use case is so ad-hoc that there isn't much to solve in general -- but I am not an expert in Cabal at all.*

I have written extensively about my use case at https://unsafeperform.io/blog/2020-05-07-integrating_verilator_and_clash_via_cabal/. Basically, depending on the value of some custom `x-` fields in the various Cabal components, I need to run some Haskell code (Clash's `defaultMain`), in a context where all Cabal dependencies are already available, in order to generate an `.hsc` file and an `.a` static library. The `hsc` file is then compiled the standard way, and the `.a` file is linked statically into the resulting exe or library.

There are at least two parts of this process that aren't directly supported by Cabal:

* Generating multiple artifacts (a static library and an `.hsc` file) by one code generator / preprocessor
* Multi-phase code generator pipeline: my tool generates an `.hsc` file, which then needs to be further processed by `hsc2hs` to get the final `.hs` file suitable for consumption by GHC.