Cannot activate extension due to unknown dependency

[ploeh]

Your environment

Which OS do you use:

Edition Windows 11 Pro
Version 23H2
Installed on ‎03.‎02.‎2024
OS build 22631.6199
Experience Windows Feature Experience Pack 1000.22700.1108.0

Steps to reproduce

Attempt to install the Haskell Visual Studio Code extension.

Expected behaviour

The Visual Studio Code extension is installed and working.

Actual behaviour

When starting Visual Studio Code, the following pop-up error message appears:

Cannot activate the 'Haskell' extension because it depends on an unknown 'justusadam.language-haskell' extension.

True to the message's content, the extension does not work.

Include debug information

Execute in the root of your project the command haskell-language-server-wrapper --debug . and paste the logs here (you can find the executable location here):

Debug output:

$ haskell-language-server-wrapper --debug .
No 'hie.yaml' found. Try to discover the project type!
Run entered for haskell-language-server-wrapper(haskell-language-server-wrapper-2.5.0.0.exe) Version 2.5.0.0 x86_64 ghc-9.4.8
Current directory: C:\Users\mark\Documents\Datalogi\AP\Exam\exam-handout
Operating system: mingw32
Arguments: ["--debug","."]
Cradle directory: C:\Users\mark\Documents\Datalogi\AP\Exam\exam-handout
Cradle type: Cabal

Tool versions found on the $PATH
cabal:          3.10.2.1
stack:          3.9.1
ghc:            9.4.8

[I've excluded the rest, which is quite extensive, reveals quite a bit about the files on my machine, and is probably not relevant to this particular issue. I will, however, provide the information if required.]

[tomdsi]

As of this morning, the extension has stopped working, and I got a different error in the extension output window. I tried reinstalling the extension and then I got this same error. Unfortunately I can not get the previous error anymore.

[EvaKlapwijk]

I have the same problem with trying to open the haskell language server (without reinstalling). This is the error output:

2026-06-12 08:49:16.4180000 [client] INFO Executing '.\"C:\ghcup\bin\haskell-language-server-wrapper-2.14.0.0.exe"
"C:\ghcup\bin\haskell-language-server-wrapper-2.14.0.0.exe"
C:\ghcup\tmp\ghcup-ghc-9.12.4_cabal-3.14.2.0_hls-2.14.0.0_stack-3.1.1\haskell-language-server-wrapper.exe --numeric-version' in cwd 'c:\Users\username\Documents\TIO'
2026-06-12 08:49:16.4800000 [client] ERROR Error executing '.\"C:\ghcup\bin\haskell-language-server-wrapper-2.14.0.0.exe"
"C:\ghcup\bin\haskell-language-server-wrapper-2.14.0.0.exe"
C:\ghcup\tmp\ghcup-ghc-9.12.4_cabal-3.14.2.0_hls-2.14.0.0_stack-3.1.1\haskell-language-server-wrapper.exe --numeric-version' with error code 1
2026-06-12 08:49:16.4800000 [client] ERROR stderr: The filename, directory name, or volume label syntax is incorrect.

[michelkocher]

I've had the same problem as well.

It looks like they removed the dependency from the marketplace:
https://marketplace.visualstudio.com/items/justusadam.language-haskell

As a workaround, I've installed the dependency from here:
https://open-vsx.org/extension/justusadam/language-haskell

[fendor]

For context as well, see the ticket haskell/vscode-haskell-syntax-highlighting#255

[JustinLiem]

I've tried to install the dependency manually, though it still doesn't work for me. I am using wsl though. Additionally, trying to run any of the 2 restart commands in the Haskell package will just return in a 'haskell.commands.{commandname} not found' for me.

[fendor]

@JustinLiem

Additionally, trying to run any of the 2 restart commands in the Haskell package will just return in a 'haskell.commands.{commandname} not found' for me.

Please follow the instructions at https://github.com/haskell/vscode-haskell#investigating-and-reporting-problems and report the errors/issues you are seeing. It is possible, that you are facing other issues than this one.

[ploeh]

@JustinLiem

Additionally, trying to run any of the 2 restart commands in the Haskell package will just return in a 'haskell.commands.{commandname} not found' for me.

Please follow the instructions at https://github.com/haskell/vscode-haskell#investigating-and-reporting-problems and report the errors/issues you are seeing. It is possible, that you are facing other issues than this one.

FWIW I had that exact problem this morning, too, which was what in the first place motivated me to uninstall and attempt to reinstall the extension.

[JustinLiem]

Please follow the instructions at https://github.com/haskell/vscode-haskell#investigating-and-reporting-problems and report the errors/issues you are seeing. It is possible, that you are facing other issues than this one.

After following all the steps, I get this from the "extension host (remote)" regarding this extension:

2026-06-12 13:28:29.720 [error] Activating extension haskell.haskell failed due to an error:
2026-06-12 13:28:29.720 [error] Error: `"/home/toxic/.ghcup/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/haskell-language-server-wrapper"
/home/toxic/.ghcup/tmp/ghcup-ghc-9.6.7_cabal-3.14.2.0_hls-2.14.0.0_stack-3.7.1/haskell-language-server-wrapper --numeric-version` exited with exit code ENOENT.
                              Consult the [Extensions Output](https://github.com/haskell/vscode-haskell#investigating-and-reporting-problems)
                              for details.
	at /home/toxic/.vscode-server/extensions/haskell.haskell-2.8.0/dist/extension.js:1:40827
	at exithandler (node:child_process:424:5)
	at ChildProcess.errorhandler (node:child_process:436:5)
	at ChildProcess.emit (node:events:521:24)
	at ChildProcess._handle.onexit (node:internal/child_process:293:12)
	at onErrorNT (node:internal/child_process:508:16)
	at process.processTicksAndRejections (node:internal/process/task_queues:90:21)

This is what is prints in "Haskell (...)":

2026-06-12 11:37:03.1220000 [client] DEBUG document selector patten: /home/toxic/infomlbs-project/**/*
2026-06-12 11:37:03.1220000 [client] INFO Support for '.cabal' files: automatic
2026-06-12 11:37:03.1220000 [client] INFO Executing '"/home/toxic/.ghcup/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/haskell-language-server-wrapper"
/home/toxic/.ghcup/tmp/ghcup-ghc-9.6.7_cabal-3.14.2.0_hls-2.14.0.0_stack-3.7.1/haskell-language-server-wrapper --numeric-version' in cwd '/home/toxic/infomlbs-project'
2026-06-12 11:37:03.1290000 [client] ERROR Error executing '"/home/toxic/.ghcup/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/haskell-language-server-wrapper"
/home/toxic/.ghcup/tmp/ghcup-ghc-9.6.7_cabal-3.14.2.0_hls-2.14.0.0_stack-3.7.1/haskell-language-server-wrapper --numeric-version' with error code ENOENT
2026-06-12 11:37:03.1290000 [client] ERROR stderr: 
2026-06-12 11:37:03.1290000 [client] ERROR Error executing '"/home/toxic/.ghcup/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/haskell-language-server-wrapper"
/home/toxic/.ghcup/tmp/ghcup-ghc-9.6.7_cabal-3.14.2.0_hls-2.14.0.0_stack-3.7.1/haskell-language-server-wrapper --numeric-version': name = Error, message = spawn "/home/toxic/.ghcup/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/hls/2.14.0.0/lib/haskell-language-server-2.14.0.0/bin/haskell-language-server-wrapper"
/home/toxic/.ghcup/tmp/ghcup-ghc-9.6.7_cabal-3.14.2.0_hls-2.14.0.0_stack-3.7.1/haskell-language-server-wrapper ENOENT

Performing any of the 2 restart commands will not print anything in any of the output panels and will just give this:

[fendor]

Thank you, yes, then the issue is the same as this one.

[fendor]

Our workaround is going to remove the explicit dependency on language-haskell. See #1377

A consequence of that is, there is no syntax highlighting provided by vscode-haskell itself. Other extensions will be needed for syntax highlighting.
Once the issue with language-haskell is resolved, we will reevaluate the situation.