[SOLVED] Error occured while (re-)installing GHC and setting up the VSCode Haskell Plugin

Error occured while (re-)installing GHC and setting up the VSCode Haskell Plugin

I was trying to setup the Haskell Plugin for VSCode and I had two seperate problems while trying.

First: The original error I faced while setting up the Haskell Plugin in VSCode was: HLS does not support GHC 9.8.4 yet.

Second: I faced a weird error while installing new GHC versions (or reinstalling old ones via --force). Whenever I installed ghc with ghcup install ghc X.X.X it started installing until [ Info ] Merging file tree from "path_xyz" to "path_zyx". but from then on nothing happend and sometimes I couldn't even exit the process with Ctrl+C

When I encountered the first problem I tried adding this:

"haskell.toolchain": {
        "ghc": "9.10.1",
        "hls": "latest",
        "cabal": "recommended"
    },

to my settings.json

but then I faced a new error:

Failed to find a HLS version for GHC 9.8.4 Executable names we failed to find: haskell-language-server-9.8.4.exe,haskell-language-server.exe

While I tried different ghc versions in order to get the plugin to work I tried installing/reinstalling different GHC versions and therefore encountered the second problem.

I tried GHC 9.10.1 for the first time, I tried reinstalling GHC 9.10.1 via --force and I tried installing GHC 9.8.4 for the first time.

For the first problem I also tried a few other things such as:

deleting the .stack-work folder in the projects directory twice
- once opening vscode after using stack setup
- and once without
I tried using ghcup set 9.10.1 but vscode still printed the same error about version 9.8.4

My laptop is running on Windows 11 and I've used Powershell to manage my Haskell related installations.

ghcup list gives me the following installations:

IS ghc   9.4.8      recommended,base-4.17.2.1 hls-powered 
I  ghc   9.8.4      base-4.19.2.0             2024-11-27 
I  ghc   9.10.1     base-4.20.0.0             hls-powered 
IS cabal 3.12.1.0   latest,recommended 
IS hls   2.9.0.1    latest,recommended 
IS stack 3.1.1      latest,recommended 
IS ghcup 0.1.30.0   latest,recommended

Solution

I had the exact same error and was finally able to solve it myself: You just need to specify a different resolver in the stack.yaml file whose GHC version is supported by the HLS. To do this, compare the pages HLS: GHC version support and Stackage: snapshots and look for a newer supported GHC version. In my case (and yours) that would be lts-22.43. To do this, simply change the snapshot in stack.yaml:

snapshot: lts-22.43

Hope this solves the problem for you!