auto-install tree-sitter parser on first .lf file open

The parser is now automatically downloaded when opening a .lf file for
the first time if curl is available. Added on_done callback to install()
for post-install actions like starting highlighting. Updated README with
nvim-treesitter as optional dependency and auto-install docs.

Author: remifan

README.md

@@ -37,6 +37,9 @@ For users who only want syntax highlighting:
 {
   "remifan/lf.nvim",
   ft = "lf",
+  dependencies = {
+    "nvim-treesitter/nvim-treesitter",  -- Optional: for incremental selection and textobjects
+  },
   config = function()
     require("lf").setup({
       enable_lsp = false,  -- Disable LSP features
@@ -59,7 +62,8 @@ For the complete experience with LSP, diagrams, and all features (Mac/Linux):
   "remifan/lf.nvim",
   ft = "lf",
   dependencies = {
-    "nvim-telescope/telescope.nvim",  -- Optional: enhanced library browser
+    "nvim-treesitter/nvim-treesitter",  -- Optional: for incremental selection and textobjects
+    "nvim-telescope/telescope.nvim",    -- Optional: enhanced library browser
   },
   -- Note: Diagram dependencies build automatically on first use
   -- No need to specify build command!
@@ -115,15 +119,13 @@ For the complete experience with LSP, diagrams, and all features (Mac/Linux):
 
 ## 🌳 Tree-sitter Setup
 
-For modern syntax highlighting, incremental selection, and textobjects:
+The tree-sitter parser is **automatically installed** the first time you open a `.lf` file (requires `curl`). You can also install or reinstall manually:
 
 ```vim
 :LFTSInstall
 ```
 
-This installs the LF tree-sitter parser and query files. Requires:
-- `nvim-treesitter` plugin
-- C compiler (gcc or clang) if compiling from source
+Pre-built parser binaries are downloaded from GitHub for Linux, macOS, and Windows (x64 and ARM64). Falls back to local compilation if the download fails.
 
 **Incremental Selection** (with nvim-treesitter configured):
 - Press `<CR>` in normal mode to start selection

ftplugin/lf.lua

@@ -1,9 +1,20 @@
 -- Filetype plugin for Lingua Franca
 -- Sets buffer-local options and configurations
 
--- Start tree-sitter highlighting if parser is available
+-- Start tree-sitter highlighting if parser is available, otherwise auto-install
 if pcall(vim.treesitter.language.inspect, "lf") then
   vim.treesitter.start(vim.api.nvim_get_current_buf(), "lf")
+elseif vim.fn.executable("curl") == 1 then
+  local bufnr = vim.api.nvim_get_current_buf()
+  require("lf.treesitter").install({
+    force = false,
+    on_done = function()
+      -- Start highlighting on the buffer that triggered the install
+      if vim.api.nvim_buf_is_valid(bufnr) then
+        pcall(vim.treesitter.start, bufnr, "lf")
+      end
+    end,
+  })
 end
 
 -- Set comment string for commentary.vim and similar plugins

lua/lf/treesitter.lua

@@ -436,29 +436,37 @@ local function install_from_local(source_path, opts, callback)
   end)
 end
 
-local function on_install_success()
+local function on_install_success(on_done)
   vim.notify("[lf.nvim] LF treesitter parser installed successfully!", vim.log.levels.INFO)
   pcall(function()
     vim._ts_remove_language("lf")
     vim.treesitter.language.add("lf")
   end)
+  if on_done then
+    on_done()
+  end
 end
 
 -- Main install function
 function M.install(opts)
   opts = opts or {}
   local force = opts.force or false
+  local on_done = opts.on_done
 
   -- Check if already installed
   if M.is_installed() and M.queries_installed() and not force then
-    vim.notify("[lf.nvim] LF treesitter parser is already installed. Use :LFTSInstall! to reinstall.", vim.log.levels.INFO)
+    if on_done then
+      on_done()
+    else
+      vim.notify("[lf.nvim] LF treesitter parser is already installed. Use :LFTSInstall! to reinstall.", vim.log.levels.INFO)
+    end
     return
   end
 
   -- Try GitHub download first
   install_from_github(function(ok, err)
     if ok then
-      on_install_success()
+      on_install_success(on_done)
       return
     end
 
@@ -481,7 +489,7 @@ function M.install(opts)
 
     install_from_local(source_path, opts, function(lok, lerr)
       if lok then
-        on_install_success()
+        on_install_success(on_done)
       else
         vim.notify("[lf.nvim] " .. (lerr or "Unknown error"), vim.log.levels.ERROR)
       end