nvim.md

Neovim setup

tree-sitter-jac works with Neovim's tree-sitter integration (nvim-treesitter). Until the parser lands in the nvim-treesitter community registry, register it manually as shown below.

This repo doubles as a Neovim plugin: it ships ftdetect/jac.lua (filetype detection for *.jac and the *.impl.jac / *.cl.jac / *.sv.jac / *.na.jac / *.test.jac variants) and ftplugin/jac.lua (commentstring, indent). Install it like any plugin to get those for free, e.g. with lazy.nvim:

{ "jaseci-labs/tree-sitter-jac" }

If you are not installing it as a plugin, add filetype detection yourself:

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

1. Register and install the parser

The snippet below targets nvim-treesitter's master branch. On the rewritten main branch the registration API differs; follow its "add a parser" docs, keeping the same url and both files (src/parser.c, src/scanner.c).

local parser_config = require("nvim-treesitter.parsers").get_parser_configs()
parser_config.jac = {
  install_info = {
    url = "https://github.com/jaseci-labs/tree-sitter-jac",
    -- BOTH files are required: the grammar uses an external scanner
    -- (src/scanner.c) for f-strings, JSX text, and `::py::` blocks.
    files = { "src/parser.c", "src/scanner.c" },
    branch = "main",
    generate_requires_npm = false, -- src/parser.c is committed
  },
  filetype = "jac",
}

Then :TSInstall jac.

For local development against a checkout, point the url at the path:

parser_config.jac.install_info.url = "/path/to/tree-sitter-jac"

2. Install the queries

:TSInstall compiles the parser but does not ship queries. They live at queries/jac/ here, which is exactly where Neovim looks on the runtimepath — so installing this repo as a plugin (above) provides them automatically. If you are not using it as a plugin, copy queries/jac/*.scm to ~/.config/nvim/queries/jac/. Provided queries:

• highlights.scm — syntax highlighting (incl. f-string interpolations & JSX)
• locals.scm — scopes & definitions
• folds.scm — foldmethod=expr folding
• injections.scm — embedded languages (inline Python, comments)
• indents.scm — indentation
• textobjects.scm — nvim-treesitter-textobjects (functions, classes, …)

::py:: … ::py:: blocks (and code-in-comments) are highlighted by injecting another language, so install that parser for it to render — e.g. :TSInstall python. The textobjects.scm motions additionally require the nvim-treesitter-textobjects plugin.

3. Folding & indentation

-- folding
vim.opt_local.foldmethod = "expr"
vim.opt_local.foldexpr = "v:lua.vim.treesitter.foldexpr()"
-- indentation: enable in your nvim-treesitter setup
require("nvim-treesitter.configs").setup({ indent = { enable = true } })

4. LSP (separate from this grammar)

Highlighting (this grammar) and semantic features (completion, hover, diagnostics, go-to-definition) are independent. For the latter, point Neovim's built-in LSP at the Jac language server, which ships with jaclang:

vim.api.nvim_create_autocmd("FileType", {
  pattern = "jac",
  callback = function(args)
    vim.lsp.start({
      name = "jac",
      cmd = { "jac", "lsp" },
      root_dir = vim.fs.root(args.buf, { "jac.toml", ".git" }),
    })
  end,
})

Once jac is added to nvim-lspconfig, this becomes require("lspconfig").jac.setup({}). The upstream tracking issue is jaseci-labs/jac#6784.