The files cabal.project and cabal.project.local_toCopy feature the following two GHC options:

• -fwrite-ide-info, which tells GHC to generate HIE files upon compilation: useful for code analysis tools such as Weeder and Calligraphy
• -hiedir=".stack-work/hiedb", which tells GHC to save HIE files in the .stack-work/hiedb directory instead of the default location.

-fwrite-ide-info is definitely useful, and should probably be left in unless it has a significant impact on build times (if it does impact performance, it could be removed and developers could add it back when they need to run code analysis tools).

-hiedir=".stack-work/hiedb", however, has no justification anymore, now that Stack is no longer the default build tool. On the other hand, it makes for a confusing experience trying to run code analysis tools only to have them fail to find where HIE files are located. It should be removed.