Nickel Language Server

The Nickel Language Server (NLS) is a language server for the Nickel programming language. NLS offers error messages, type hints, and auto-completion right in your favorite LSP-enabled editor.

NLS is a stand-alone binary. Once built, you must then configure you code editor to use it for Nickel source files. This document covers building NLS and using it in VSCode and (Neo)Vim.

Installation

Three installation methods are proposed: using Nix flakes (recommended), using Nix without flakes (older Nix versions), or using cargo if you already use the Rust toolchain and don't want to install Nix.

Using Nix (flakes)

The easiest way to install nls is using Nix.

Important: the following of this section assumes that you have a flake-enabled Nix (>= 2.4) and the experimental features flakes and nix-command enabled. At the time of writing, the current stable version of Nix is flake-enabled. If you haven't enabled any experimental feature globally or don't know what it is even about, just append --experimental-features "flakes nix-command" to all of the following commands.

• Global installation: if you want to use nls on a regular basis, this is what you want to do. To have nickel and nls available globally, add them into your profile:

  nix profile install github:tweag/nickel

• Shell: Try out for the time of a session. To be dropped in a shell with the nickel and nls commands available, run:

  nix shell github:tweag/nickel

• Local build: if you just wand to build nickel and nls without installing them (the executables will be placed in ./result/bin/):

  nix build github:tweag/nickel

Using Nix (without flakes)

Alternatively, you can install nickel and nls globally on older Nix versions without flakes via nix-env:

git clone https://github.com/tweag/nickel.git
cd nickel
nix-env -f . -i

Using Cargo

If you already have a working cargo installation, you can make nls available globally without Nix:

cargo install nickel-lang-lsp

WARNING: the 0.1.0 version of the NLS crate (nickel-lang-lsp) doesn't correctly define the name of the binary as nls. If you can't find nls after a successful cargo installation, try to run nickel-lang-lsp --version. If this command is available, you'll have to substitute nls for nickel-lang-lsp in the instructions that follow.

Interfacing with editors

Once the nls binary is available, you can proceed with the configuration of your editor.

VS Code

Build the extension

NLS is currently not available through the vscode marketplace, but this repository includes an extension that can be built locally via Nix (see the section about the Nix setup).

• One-liner (using the jq command):

  code --install-extension $(nix build ./\#vscodeExtension --no-link --json | jq ".[0].outputs.vsix")

• In two steps, going via VSCode:

  • Build with Nix:

    nix build github:tweag/nickel#vscodeExtension

  • Then, in VSCode, use "Extension: Install from VSIX" in the vscode command palette and choose ./result-vsix/nls-client.vsix.

Configuration

The VS Code extension offers three configuration options:

• nls.server.path: Path to nickel language server
• nls.server.trace: Enables performance tracing to the given file
• nls.server.debugLog: Logs the communication between VS Code and the language server.

(Neo)Vim

Before proceeding install the Nickel syntax highlighting plugin using your Vim plugin manager. Without this plugin your LSP client may not start NLS on nickel source files.

With Vim-Plug:

Plug 'nickel-lang/vim-nickel'

Neovim builtin LSP

nls is supported in nvim-lspconfig. Using nvim-lspconfig setup nls like all your other LSP servers as described by the nvim-lspconfig ReadMe.

require('lspconfig')["nickel_ls"].setup {}

With Coc.nvim

Add an nickel_ls entry to your configuration. Type :CocConfig in Neovim (or edit coc-settings.json) and add:

{
  "languageserver": {
    // Your other language servers configuration
    // ...,
    "nickel_ls": {
      "command": "nls",
      // You can enable performance tracing with:
      // "command": "nls --trace <file>",
      "rootPatterns": [
        ".git"
      ],
      "filetypes": [
        "ncl"
      ]
    }
  }
}

Emacs

Follow the instructions on the the nickel-mode repo.