Setup Troubleshooting

This page serves as a dumping ground for setup problems and their resolutions. We recommend everyone first runs ghcide on the console to check what files in their project load, and only the moves on to using ghcide through an editor (e.g. VS Code).

"mismatched interface file versions"

If you see a problem such as:

File:     ./test/Spec.hs
Range:    1:0-1:0
Source:   typecheck
Severity: DsError
Message:
  test/Spec.hs:1:1: error:
  Bad interface file:
  /Users/daml/.stack/programs/x86_64-osx/ghc-8.6.4/lib/ghc-8.6.4/base-4.12.0.0/Prelude.hi
  mismatched interface file versions (wanted "8065", got "8064")

The cause is that your program is configured to use a different GHC to the one you built ghcide with. In ghcide you can view the version number it was compiled with on the first line as:

ghcide version: 0.0.3 (GHC: 8.6.5)

You can see the version of GHC being used by this project in the second-last line of the output with ghc-8.6.4/, or in in mismatch interfaces of wanted 8065 (aka 8.6.5), got 8064 (aka 8.6.4). The solution is to use the same GHC version in both places.

“failed to load interface for ‘…’ There are files missing”

If you see a problem such as:

File:     ./src/File/FileStream.hs
Range:    1:0-100001:0
Source:   typecheck
Severity: DsError
Message: 
  Program error: Failed to load interface for ‘Data.DList’
Files that failed:
  There are files missing in the ‘dlist-0.8.0.7’ package,
 * ./src/File/FileStream.hs
  try running 'ghc-pkg check'.
  Use -v to see a list of the files searched for.

It might be caused by ghcide picking up the wrong cradle. In particular, this has been observed when running in a nix-shell where ghcide picked up the default cradle. Try setting the cradle explicitly, e.g., to use the cabal cradle create a hie.yaml file with the following content:

cradle: {cabal: {component: "mylibrary"}}

ghc: readCreateProcess: does not exist

I was getting this in Windows: ghcide.exe: ghc: readCreateProcess: does not exist (No such file or directory)

And we figured a hack around for this:

VSCode user or workspace settings, add these:

"hic.executablePath": "stack",
"hic.arguments": "exec ghcide -- --lsp"

Since I use stack. Required if you don't have a ghc on your path.

Could not find module ...

Try adding an explicit hie.yaml file and see if that helps.

Works in `ghcide` but not my editor

Does ghcide alone work on the console? Did you first enter a Nix shell? Or run stack exec ghcide? If so, there are two options:

Run your editor via the same mechanism, e.g. stack exec code.
Change the extension to use the executable as stack and the arguments as exec -- ghcide --lsp.

Issues with Nix

If you are using packages installed by Nix, then often Nix will set NIX_GHC_LIBDIR to say where the libraries are installed. ghcide can cope with that. However, sometimes the ghc on your shell will actually be a shell script that sets NIX_GHC_LIBDIR, which ghcide can't find. If that happens, you need to either set NIX_GHC_LIBDIR (so ghcide can see it) or use a proper Nix compatible wrapper over ghcide.

ghcide: this operation requires -fexternal-interpreter

This can happen if you have a GHC compiled without GHC library support. This seems to be the case with haskell.nix at the moment.

Symbol’s value as variable is void: capability

As described here and here, the default installation of lsp-mode, lsp-ui, lsp-ui-mode and lsp-haskell as described in ghcide's "Using with Emacs" section may result in the following error message:

Symbol’s value as variable is void: capability

This can be caused by either an old version of the Emacs package dash, or a cached .elc file for an old version. A fix consists of (re)moving the old package from ~/.emacs.d/elpa/ and installing it again, e.g. via M-x package-list-packages RET and M-x package-install RET dash RET. If this is not enough,

find ~/.emacs.d -name '*.elc' -exec rm {} \;

(which causes recompilation of all bytecode-compiled scripts.)

Docker stack builds

You're likely to see ghcide: (ExitFailure 1,"",""). Because ghcide can't get at the ghc installed inside Docker, your best bet is to stack exec ghcide and make sure ghcide is installed within the container. Full details at issue 221.

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