vim: Make sure treesitter updates parse tree when text changes (#32)

In the current implementation of treesitter, the parse tree for the
current buffer would not be automatically updated/refreshed when
text changes, unless treesitter-highlight module is enabled.
However, I don't want to use treesitter's highlight/syntax feature yet
due to some issues and conflicts.

To make the parse tree up-to-date as text changes, parser:parse()
needs to be explicitly called in the absence of treesitter-highlight.

Ref: nvim-treesitter/nvim-treesitter#2492

nvim/lua/config/treesitter.lua

@@ -1,7 +1,10 @@
 -- Treesitter config
 -- https://github.com/nvim-treesitter/nvim-treesitter
 
-require'nvim-treesitter.configs'.setup {
+local ts_configs = require("nvim-treesitter.configs")
+local ts_parsers = require("nvim-treesitter.parsers")
+
+ts_configs.setup {
  -- one of "all", "maintained" (parsers with maintainers), or a list of languages
   ensure_installed = "maintained",
 
@@ -10,6 +13,23 @@ require'nvim-treesitter.configs'.setup {
     "phpdoc",      -- Not compatible with M1 mac
   },
 
+  highlight = {
+    -- TreeSitter's highlight/syntax support is yet experimental and has some issues.
+    -- It overrides legacy filetype-based vim syntax, and colorscheme needs to be treesitter-aware.
+    enable = false,   -- TODO: Enable again when it becomes mature and usable enough.
+
+    -- List of language that will be disabled.
+    -- For example, some non-programming-language filetypes (e.g., fzf) should be
+    -- explicitly turned off otherwise it will slow down the window.
+    disable = { "fzf", "GV", "gitmessengerpopup", "fugitive", "NvimTree" },
+
+    -- Setting this to true will run `:h syntax` and tree-sitter at the same time.
+    -- Set this to `true` if you depend on 'syntax' being enabled (like for indentation).
+    -- Using this option may slow down your editor, and you may see some duplicate highlights.
+    -- Instead of true it can also be a list of languages
+    additional_vim_regex_highlighting = { "python" },
+  },
+
   playground = {
     enable = true,
     updatetime = 30,
@@ -28,6 +48,40 @@ require'nvim-treesitter.configs'.setup {
   },
 }
 
+-- Make sure TS syntax tree is updated when needed by plugin (with some throttling)
+-- even if the `highlight` module is not enabled.
+-- See https://github.com/nvim-treesitter/nvim-treesitter/issues/2492
+_G.TreesitterParse = function()
+  local lang = ts_parsers.ft_to_lang(vim.bo.filetype)
+  local parser = ts_parsers.get_parser(vim.fn.bufnr(), lang)
+  if parser then
+    return parser:parse()
+  else
+    return false
+  end
+end
+local function throttle(fn, ms)
+  local timer = vim.loop.new_timer()
+  local running = false
+  return function(...)
+    if not running then
+      timer:start(ms, 0, function() running = false end)
+      running = true
+      pcall(vim.schedule_wrap(fn), select(1, ...))
+    end
+  end
+end
+if not ts_configs.get_module('highlight').enable then
+  _G.TreesitterParseDebounce = throttle(_G.TreesitterParse, 100)  -- 100 ms
+  vim.cmd [[
+    augroup TreesitterUpdateParsing
+      autocmd!
+      autocmd TextChanged,TextChangedI *   call v:lua.TreesitterParseDebounce()
+    augroup END
+  ]]
+end
+
+
 -- Folding support
 vim.o.foldmethod = 'expr'
 vim.o.foldexpr = 'nvim_treesitter#foldexpr()'