I think these steps would reproduce the issue I have found:
Build haskell-language-server with -fwrite-ide-info enabled with cabal HEAD
(assuming there is already an hiedb initialized for hacking on haskell-language-server): $(cabal list-bin ghcide) hiedb index ~/.cabal/store/aeson-[hash]
$(cabal list-bin ghcide) hiedb name-def parseJSON -- I believe this will fail
I think these steps would reproduce the issue I have found:
-fwrite-ide-info
enabled with cabal HEAD