Fails to connect to a Agda Language Server running on NixOS on WSL

[VladimirMarko]

I am on Windows 10 and I want to write some Agda code.

The HoTT Game recommends that I install NixOS on WSL2 and run Agda there.

So I installed NioOS using wsl --import NixOS .\NixOS\ nixos-wsl.tar.gz --version 2 as described in NixOS-WSL.

Now, the current version of NixOS-WSL does not support VS Code out of the box (issue here), so I used this flake to fix that, as recommended in the issue.

That means that my current configuration is as follows:
NixOS in WSL2 on Windows 10 with /etc/nixos/ containing:

1. flake.nix:

{
  description = "A configuration flake for WSL2 NixOS with VS Code";

  inputs = {
    nixos-wsl-vscode.url = "github:Atry/nixos-wsl-vscode";
  };

  outputs = { self, nixpkgs, nixos-wsl-vscode }: {
    nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        nixos-wsl-vscode.nixosModules.vscodeServerWsl
        ({ config, pkgs, ... }: {
          # rest of your configuration
        })
        ./configuration.nix
      ];
    };
  };
}

2. configuration.nix:

# Edit this configuration file to define what should be installed on
# your system. Help is available in the configuration.nix(5) man page, on
# https://search.nixos.org/options and in the NixOS manual (`nixos-help`).

# NixOS-WSL specific options are documented on the NixOS-WSL repository:
# https://github.com/nix-community/NixOS-WSL

{ config, lib, pkgs, ... }:

{
  imports = [
  ];

  wsl.enable = true;
  wsl.defaultUser = "nixos";

  nix.settings.experimental-features = [
    "nix-command"
    "flakes"
  ];


  # This value determines the NixOS release from which the default
  # settings for stateful data, like file locations and database versions
  # on your system were taken. It's perfectly fine and recommended to leave
  # this value at the release version of the first install of this system.
  # Before changing this value read the documentation for this option
  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
  system.stateVersion = "23.11"; # Did you read the comment?
}

Additionally, I have a project folder ~/agda-test containing:

1. flake.nix:

{
  description = "An Agda shell";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
  };

  outputs = { self, nixpkgs }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};
    in
    {
      devShells.${system}.default =
        pkgs.mkShell
          {
            buildInputs = [
              (pkgs.agda.withPackages (ps: [
                ps.standard-library
                ps.cubical
              ]))
            ];
          };
  };
}

2. AgdaTest.agda with some Agda code.

Now, in this folder (~/agda-test) I run:

1. nix develop
2. code .

This opens the folder in VS Code in Windows, as intended.

I open AgdaTest.agda in this VS Code instance, go C-c C-l and it fails.

I initially got this error:

[Error - 8:09:49 AM] Server initialization failed.
  Message: write EPIPE
  Code: -32099 
[Error - 8:09:49 AM] Agda Language Server client: couldn't create connection to server.
  Message: write EPIPE
  Code: -32099 
/home/nixos/.vscode-server/data/User/globalStorage/banacorn.agda-mode/v0.2.6.4.0.3-linux/als: /home/nixos/.vscode-server/data/User/globalStorage/banacorn.agda-mode/v0.2.6.4.0.3-linux/als: cannot execute binary file

I tried doing chmod a+x als, but this had no effect - the error persisted as it was despite the added permission, and I subsequently reversed that change.

Now, writing this issue, I restarted everything and seemingly spontaneously got a different error after C-c C-l:

[Error - 8:52:12 AM] Agda Language Server client: couldn't create connection to server.
Launching server using command /home/nixos/.vscode-server/data/User/globalStorage/banacorn.agda-mode/v0.2.6.4.0.3-linux/als failed. Error: spawn /home/nixos/.vscode-server/data/User/globalStorage/banacorn.agda-mode/v0.2.6.4.0.3-linux/als EACCES

[liammcdermott]

On the other end of the complexity spectrum, I have this error on stock Ubuntu 23.10, loading the language server through VSCode (1.87.0) and this extension.

The steps I took:

1. Have Ubuntu 23.10 and VSCode 1.87.0 installed
2. In VSCode, install agda-mode
3. From the extension's page, click the cog → Extension settings → tick the box 'Connect to Agda Language Server (experimental)'
4. Open an Agda file, and press C-c C-l
5. Get the error in the screenshot below (and the same as OP)

The only difference I'm seeing is restarting does not give me a different error. I can reproduce this every time I open VSCode and C-c C-l in an Agda file.

Edit: I also seem to be experiencing #139

[mtoohey31]

I believe the NixOS issue is happening because als has dynamic library dependencies which likely aren't satisfied due to the NixOS environment. You'll probably need to figure out how to install als manually so it's built to work under NixOS. I haven't managed to find a derivation for it yet though...

The alternative is to use something like nix-ld to add the dependencies to your environment, but I couldn't get this to work cause VSCode/agda-mode-vscode (not sure which) doesn't seem to be respecting the environment variables I've set before launching VSCode. My temporary workaround is to launch the downloaded (unpatched) als inside the following flake's devshell:

{
  description = "agda-env";

  inputs = {
    nixpkgs.url = "nixpkgs/nixpkgs-unstable";
    utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, utils }: utils.lib.eachDefaultSystem (system:
    let
      pkgs = import nixpkgs { inherit system; };
      inherit (pkgs) agda gmp icu70 lib libz mkShell ncurses stdenv vscode;
    in
    {
      devShells.default = mkShell {
        packages = [ agda vscode ];

        NIX_LD_LIBRARY_PATH = lib.makeLibraryPath [
          gmp
          icu70
          libz
          ncurses
        ];

        NIX_LD = builtins.readFile "${stdenv.cc}/nix-support/dynamic-linker";
      };
    });
}

...by running:

Agda_datadir=$HOME/.config/Code/User/globalStorage/banacorn.agda-mode/v0.2.6.4.0.3-linux/data/ $HOME/.config/Code/User/globalStorage/banacorn.agda-mode/v0.2.6.4.0.3-linux/als -p

(You may need to adjust some paths.)

Edit: after using this some more, I'm having trouble with imports, and I haven't figured out why yet. So even this workaround doesn't appear to be a complete solution.

[Educorreia932]

You can instead try to install the standard library manually as described here, which should work.