Re: structured error messages

Ultimately, if reading error messages did require linking with GHC, it wouldn't be the end of the world.  I would just write my own translation layer to JSON.  So consider this a weak preference.

I think this is the key. Ultimately, all other uses can be done on top of just linking GHC the library. Just as we have ghc-lib to paper over the differences between GHC versions and save individual projects from developing their own comparability layers, so we could also have some ghc-json library and tweaked frontend executable or something. The GHC repo has stringent CI and is somewhat a bottleneck already, so the more we can do out-of-band, the better, I say. John