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).
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:
```console
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.
Try adding an explicit `hie.yaml` file and see if that helps.
## Ambiguous main module
```console
$ stack exec ghcide
...
ghcide: CradleError (ExitFailure 1) ["Failed to parse result of calling stack","","* * ** ** **","The main module to load is ambiguous. Candidates are: ","1. Package `mypackage' component mypackage:exe:mypackage-exe with main-is file: /home/user/mypackage/app/Main.hs","2. Package `mypackage' component mypackage:exe:otherbin-exe with main-is file: /home/user/mypackage/app/otherbin.hs","You can specify which one to pick by: "," * Specifying targets to stack ghci e.g. stack ghci mypackage:exe:mypackage-exe"," * Specifying what the main is e.g. stack ghci --main-is mypackage:exe:mypackage-exe"," * Choosing from the candidate above [1..2]","* * ** ** * *","","<stdin>: hGetLine: end of file"]
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:
1. Run your editor via the same mechanism, e.g. `stack exec code`.
2. 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](https://github.com/hercules-ci/ghcide-nix) 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](https://github.com/input-output-hk/haskell.nix/issues/313) with `haskell.nix` at the moment.
As described [here](https://github.com/emacs-lsp/lsp-mode/issues/770#issuecomment-483540119) and [here](https://github.com/emacs-lsp/lsp-mode/issues/517#issuecomment-445448700), the default installation of `lsp-mode`, `lsp-ui`, `lsp-ui-mode` and `lsp-haskell` as described in [ghcide's "Using with Emacs" section](https://github.com/haskell/ghcide/#using-with-emacs) may result in the following error message:
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.)
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](https://github.com/haskell/ghcide/issues/221).
ghcide.exe: CradleError (ExitFailure 1) ["Failed to parse result of calling stack","'stty' is not recognized as an internal or external command,","operable program or batch file."
It is fixed for stack-2.3.1 so upgrading your stack installation is the recommended action. However, there is a workaround for earlier versions described here: https://github.com/haskell/haskell-ide-engine/issues/1428#issuecomment-547530794.