feat: don't depend on nvim-treesitter for tree-sitter features

Author: Marc Jakobi

CHANGELOG.md

@@ -6,6 +6,13 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Added
+
+- Use tree-sitter if the parser for Haskell is installed,
+  without requiring the nvim-treesitter plugin.
+
 ## [1.1.0] - 2023-11-05
 
 ### Added

README.md

@@ -49,7 +49,8 @@ Use luarocks or your favourite plugin manager.
 - [`haskell-language-server`](https://haskell-language-server.readthedocs.io/en/latest/installation.html)
   and [`haskell-tools.nvim`](https://github.com/mrcjkb/haskell-tools.nvim)
   (some snippets work better with LSP).
-- [`nvim-treesitter`](https://github.com/nvim-treesitter/nvim-treesitter)
+- A Haskell tree-sitter parser or
+  [`nvim-treesitter`](https://github.com/nvim-treesitter/nvim-treesitter)
   and the parser for haskell.
 
 ## Quick setup

lua/haskell-snippets/module.lua

@@ -24,7 +24,8 @@ local choice = ls.choice_node
 local dynamic = ls.dynamic_node
 
 local has_treesitter, parsers = pcall(require, 'nvim-treesitter.parsers')
-local hs_lang = has_treesitter and parsers.ft_to_lang('haskell')
+local hs_lang = has_treesitter and parsers.ft_to_lang('haskell') or 'haskell'
+local has_haskell_parser = pcall(vim.treesitter.get_string_parser, '', 'haskell')
 
 local function get_module_name_node()
   local module_name = util.lsp_get_module_name()
@@ -77,7 +78,7 @@ local function get_qualified_name_node(args)
   end
   local import_stmt = 'import qualified ' .. module_name
   local choices = { insert(1) }
-  if hs_lang then
+  if has_haskell_parser then
     local module_query = vim.treesitter.query.parse(hs_lang, '(module) @mod')
     local lang_tree = vim.treesitter.get_string_parser(import_stmt, hs_lang, { injections = { [hs_lang] = '' } })
     local root = fast_parse(lang_tree):root()