I'm new to haskell so I don't have deep understanding about how ghc-mod works and how cabal-install-like build tools of haskell worlds move under the hood.
But I somehow found vim haskell plugins from github, including neco-ghc auto completion plugin powered by ghc-mod which seemed very attractive to me.
The problem was that it only works on project-level haskell source codes of cabal-install initialized projects while it doesn't work at all on stack-initialized projects.
My directory structure is generated by following commands:
~ $ mkdir my_project && cd my_project
~/my_project $ cabal init
~/my_project $ cabal sandbox init
which yields
my_project
|-- Setup.hs
|-- cabal.sandbox.config
|-- src / Lib.hs
Autocompletion works (it suggests Prelude module's keywords) when I edit Setup.hs but I suggests nothing when I try edit src/Lib.hs.
My :NecoGhcDiagnotics command outputs
Current filetype: haskell
ghc-mod is executable: 1
omnifunc: necoghc#omnifunc
neocomplete.vim: 0
neocomplcache.vim: 2
YouCompleteMe: 0
vimproc.vim: 900
ghc-mod: 5.4.0.0
Imported modules: Prelude
Number of symbols in Prelude: 0
when I edit src/Lib.hs while
Current filetype: haskell
ghc-mod is executable: 1
omnifunc: necoghc#omnifunc
neocomplete.vim: 0
neocomplcache.vim: 2
YouCompleteMe: 0
vimproc.vim: 900
ghc-mod: 5.4.0.0
Imported modules: Distribution.Simple, Prelude
Number of symbols in Prelude: 235
is the output of the command when I'm editing Setup.hs.
It clearly looks like ghc-mod is not detecting any symbols when I'm editing src/Lib.hs.. why is this happening?
Posting an answer as requested: ghc-mod 5.4.0 insists to be run from the project's root directory. This breaks various third-party programs that depend on ghc-mod. The neco-ghc plugin has been updated to cope with that, other programs are dropping support for ghc-mod.