hie-bios is the way to specify how haskell-language-server and ghcide set
up a GHC API session.

Given a Haskell project that is managed by Stack, Cabal, or other package
tools, haskell-language-server needs to know the full set of flags to pass
to GHC in order to build the project. These flags might contain some
compilation options like -O2, but a lot of the time they are package
dependencies such as -package-id directory-1.3.6.0, which also need to be
built beforehand. hie-bios satisfies both these needs.