Editor Setup

This guide covers how to get syntax highlighting, indentation, and code folding for .bnf files in Neovim and Helix.

---

Neovim (nvim-treesitter)

1 — Register the parser

Add the following to your Neovim config (e.g. init.lua) before the nvim-treesitter setup call:

local parser_config = require("nvim-treesitter.parsers").get_parser_configs()

parser_config.bnf = {
  install_info = {
    url = "https://github.com/ambs/tree-sitter-bnf-tools",
    files = { "tree-sitter-bnf/src/parser.c" },
    branch = "main",
  },
  filetype = "bnf",
}

2 — Install the parser

Inside Neovim, run:

:TSInstall bnf

3 — Register the filetype

Neovim does not associate .bnf files with the bnf filetype automatically. Add this to your config:

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

4 — Install the query files

Copy (or symlink) the query files from the repository into your Neovim runtime:

QUERIES_SRC="<path-to-repo>/tree-sitter-bnf/queries"
QUERIES_DEST="$HOME/.config/nvim/queries/bnf"

mkdir -p "$QUERIES_DEST"
cp "$QUERIES_SRC/highlights.scm" "$QUERIES_DEST/"
cp "$QUERIES_SRC/indents.scm"    "$QUERIES_DEST/"
cp "$QUERIES_SRC/folds.scm"      "$QUERIES_DEST/"

5 — Enable folding (optional)

To use tree-sitter-based folding, add this to your config or a ftplugin/bnf.lua file:

vim.opt_local.foldmethod = "expr"
vim.opt_local.foldexpr   = "nvim_treesitter#foldexpr()"
vim.opt_local.foldenable  = false   -- open all folds by default

---

Helix

1 — Build the parser

Clone the repository and compile the parser:

git clone https://github.com/ambs/tree-sitter-bnf-tools
cd tree-sitter-bnf-tools/tree-sitter-bnf
tree-sitter generate   # only needed if grammar.js changed
gcc -shared -o bnf.so -fPIC src/parser.c

2 — Install the parser

Place the compiled shared library where Helix expects it:

mkdir -p ~/.config/helix/runtime/grammars
cp bnf.so ~/.config/helix/runtime/grammars/

3 — Install the query files

QUERIES_DEST="$HOME/.config/helix/runtime/queries/bnf"
QUERIES_SRC="<path-to-repo>/tree-sitter-bnf/queries"

mkdir -p "$QUERIES_DEST"
cp "$QUERIES_SRC/highlights.scm" "$QUERIES_DEST/"
cp "$QUERIES_SRC/indents.scm"    "$QUERIES_DEST/"

4 — Register the language

Add the following to ~/.config/helix/languages.toml:

[[language]]
name        = "bnf"
scope       = "source.bnf"
file-types  = ["bnf"]
roots       = []
comment-token = "#"

[[grammar]]
name   = "bnf"
source = { path = "<path-to-repo>/tree-sitter-bnf" }

Open a .bnf file and run :lang-support to confirm the language is active.