Editor setup

Harn ships a capable language server, harn-lsp, that powers diagnostics, completions, go-to-definition, hover, rename, formatting, and code actions. The install script puts harn-lsp on your PATH alongside harn and harn-dap, so any editor with a generic LSP client can light up Harn support by pointing at that one binary.

harn-lsp takes no arguments and speaks the Language Server Protocol over stdin/stdout. Every editor below launches it the same way — harn-lsp with no flags — and maps the .harn file extension to the harn language id.

For the full capability matrix (every LSP feature, the DAP debugger, and the tree-sitter grammar) see Editor integration.

VS Code

The richest experience is the bundled extension in editors/vscode/, which wires up the LSP and DAP clients, syntax highlighting, snippets, and the Harn: Run Pipeline / Harn: Format File commands automatically.

Once it is published you will be able to install it from the Marketplace or Open VSX by searching for Harn Language. Until then, build and install it locally:

cd editors/vscode && npm install && npm run compile && npx @vscode/vsce package

Then run Extensions: Install from VSIX… from the command palette and pick the generated harn-lang-0.1.0.vsix.

The extension starts harn-lsp from your PATH by default. Set harn.lspPath in your settings if the binary lives somewhere else.

Neovim

Neovim's built-in LSP client (0.11+) can start harn-lsp directly. First register the .harn filetype, then configure and enable the server. Add this to your config (for example ~/.config/nvim/init.lua):

-- Map the .harn extension to a `harn` filetype.
vim.filetype.add({ extension = { harn = "harn" } })

-- Configure the Harn language server (harn-lsp must be on your PATH).
vim.lsp.config("harn", {
  cmd = { "harn-lsp" },
  filetypes = { "harn" },
  root_markers = { "harn.toml", ".git" },
})
vim.lsp.enable("harn")

On older Neovim releases that ship nvim-lspconfig, the equivalent is:

vim.filetype.add({ extension = { harn = "harn" } })

local configs = require("lspconfig.configs")
local lspconfig = require("lspconfig")
if not configs.harn then
  configs.harn = {
    default_config = {
      cmd = { "harn-lsp" },
      filetypes = { "harn" },
      root_dir = lspconfig.util.root_pattern("harn.toml", ".git"),
    },
  }
end
lspconfig.harn.setup({})

Open any .harn file and run :LspInfo (or :checkhealth lsp) to confirm the harn client attached. Diagnostics, gd (go-to-definition), K (hover), and vim.lsp.buf.format() will all work through harn-lsp.

Zed

Zed configures external language servers through its settings.json (Zed → Settings, or ~/.config/zed/settings.json). Map the .harn extension to a language and register harn-lsp as its server:

{
  "file_types": {
    "Harn": ["harn"]
  },
  "lsp": {
    "harn-lsp": {
      "binary": {
        "path": "harn-lsp",
        "arguments": []
      }
    }
  },
  "languages": {
    "Harn": {
      "language_servers": ["harn-lsp"]
    }
  }
}

Zed resolves a bare path against your PATH, so the installed harn-lsp binary is picked up with no absolute path. Reopen a .harn file and the Harn language server starts automatically, giving you diagnostics, completions, hover, and go-to-definition.

Other editors

Any editor with a generic LSP client — Helix, Emacs (eglot/lsp-mode), Sublime Text (LSP), Kate — follows the same recipe: launch harn-lsp with no arguments for .harn files. See Editor integration for the full capability list and the tree-sitter grammar that adds syntax highlighting in tree-sitter-based editors.