neovim/runtime/lua/vim/treesitter/highlighter.lua

local a = vim.api
local query = require('vim.treesitter.query')

-- support reload for quick experimentation
local TSHighlighter = rawget(vim.treesitter, 'TSHighlighter') or {}
TSHighlighter.__index = TSHighlighter

TSHighlighter.active = TSHighlighter.active or {}

local TSHighlighterQuery = {}
TSHighlighterQuery.__index = TSHighlighterQuery

local ns = a.nvim_create_namespace('treesitter/highlighter')

---@private
function TSHighlighterQuery.new(lang, query_string)
  local self = setmetatable({}, { __index = TSHighlighterQuery })

  self.hl_cache = setmetatable({}, {
    __index = function(table, capture)
      local name = self._query.captures[capture]
      local id = 0
      if not vim.startswith(name, '_') then
        id = a.nvim_get_hl_id_by_name('@' .. name .. '.' .. lang)
      end

      rawset(table, capture, id)
      return id
    end,
  })

  if query_string then
    self._query = query.parse_query(lang, query_string)
  else
    self._query = query.get_query(lang, 'highlights')
  end

  return self
end

---@private
function TSHighlighterQuery:query()
  return self._query
end

--- Creates a new highlighter using @param tree
---
---@param tree The language tree to use for highlighting
---@param opts Table used to configure the highlighter
---           - queries: Table to overwrite queries used by the highlighter
function TSHighlighter.new(tree, opts)
  local self = setmetatable({}, TSHighlighter)

  if type(tree:source()) ~= 'number' then
    error('TSHighlighter can not be used with a string parser source.')
  end

  opts = opts or {}
  self.tree = tree
  tree:register_cbs({
    on_changedtree = function(...)
      self:on_changedtree(...)
    end,
    on_bytes = function(...)
      self:on_bytes(...)
    end,
    on_detach = function(...)
      self:on_detach(...)
    end,
  })

  self.bufnr = tree:source()
  self.edit_count = 0
  self.redraw_count = 0
  self.line_count = {}
  -- A map of highlight states.
  -- This state is kept during rendering across each line update.
  self._highlight_states = {}
  self._queries = {}

  -- Queries for a specific language can be overridden by a custom
  -- string query... if one is not provided it will be looked up by file.
  if opts.queries then
    for lang, query_string in pairs(opts.queries) do
      self._queries[lang] = TSHighlighterQuery.new(lang, query_string)
    end
  end

  a.nvim_buf_set_option(self.bufnr, 'syntax', '')

  TSHighlighter.active[self.bufnr] = self

  -- Tricky: if syntax hasn't been enabled, we need to reload color scheme
  -- but use synload.vim rather than syntax.vim to not enable
  -- syntax FileType autocmds. Later on we should integrate with the
  -- `:syntax` and `set syntax=...` machinery properly.
  if vim.g.syntax_on ~= 1 then
    vim.api.nvim_command('runtime! syntax/synload.vim')
  end
  vim.bo[self.bufnr].spelloptions = 'noplainbuffer'

  self.tree:parse()

  return self
end

--- Removes all internal references to the highlighter
function TSHighlighter:destroy()
  if TSHighlighter.active[self.bufnr] then
    TSHighlighter.active[self.bufnr] = nil
  end
end

---@private
function TSHighlighter:get_highlight_state(tstree)
  if not self._highlight_states[tstree] then
    self._highlight_states[tstree] = {
      next_row = 0,
      iter = nil,
    }
  end

  return self._highlight_states[tstree]
end

---@private
function TSHighlighter:reset_highlight_state()
  self._highlight_states = {}
end

---@private
function TSHighlighter:on_bytes(_, _, start_row, _, _, _, _, _, new_end)
  a.nvim__buf_redraw_range(self.bufnr, start_row, start_row + new_end + 1)
end

---@private
function TSHighlighter:on_detach()
  self:destroy()
end

---@private
function TSHighlighter:on_changedtree(changes)
  for _, ch in ipairs(changes or {}) do
    a.nvim__buf_redraw_range(self.bufnr, ch[1], ch[3] + 1)
  end
end

--- Gets the query used for @param lang
---
---@param lang A language used by the highlighter.
function TSHighlighter:get_query(lang)
  if not self._queries[lang] then
    self._queries[lang] = TSHighlighterQuery.new(lang)
  end

  return self._queries[lang]
end

---@private
local function on_line_impl(self, buf, line, spell)
  self.tree:for_each_tree(function(tstree, tree)
    if not tstree then
      return
    end

    local root_node = tstree:root()
    local root_start_row, _, root_end_row, _ = root_node:range()

    -- Only worry about trees within the line range
    if root_start_row > line or root_end_row < line then
      return
    end

    local state = self:get_highlight_state(tstree)
    local highlighter_query = self:get_query(tree:lang())

    -- Some injected languages may not have highlight queries.
    if not highlighter_query:query() then
      return
    end

    if state.iter == nil or state.next_row < line then
      state.iter =
        highlighter_query:query():iter_captures(root_node, self.bufnr, line, root_end_row + 1)
    end

    while line >= state.next_row do
      local capture, node, metadata = state.iter()

      if capture == nil then
        break
      end

      local start_row, start_col, end_row, end_col = node:range()
      local hl = highlighter_query.hl_cache[capture]

      local is_spell = highlighter_query:query().captures[capture] == 'spell'

      if hl and end_row >= line and (not spell or is_spell) then
        a.nvim_buf_set_extmark(buf, ns, start_row, start_col, {
          end_line = end_row,
          end_col = end_col,
          hl_group = hl,
          ephemeral = true,
          priority = tonumber(metadata.priority) or 100, -- Low but leaves room below
          conceal = metadata.conceal,
          spell = is_spell,
        })
      end
      if start_row > line then
        state.next_row = start_row
      end
    end
  end, true)
end

---@private
function TSHighlighter._on_line(_, _win, buf, line, _)
  local self = TSHighlighter.active[buf]
  if not self then
    return
  end

  on_line_impl(self, buf, line, false)
end

---@private
function TSHighlighter._on_spell_nav(_, _, buf, srow, _, erow, _)
  local self = TSHighlighter.active[buf]
  if not self then
    return
  end

  self:reset_highlight_state()

  for row = srow, erow do
    on_line_impl(self, buf, row, true)
  end
end

---@private
function TSHighlighter._on_buf(_, buf)
  local self = TSHighlighter.active[buf]
  if self then
    self.tree:parse()
  end
end

---@private
function TSHighlighter._on_win(_, _win, buf, _topline)
  local self = TSHighlighter.active[buf]
  if not self then
    return false
  end

  self:reset_highlight_state()
  self.redraw_count = self.redraw_count + 1
  return true
end

a.nvim_set_decoration_provider(ns, {
  on_buf = TSHighlighter._on_buf,
  on_win = TSHighlighter._on_win,
  on_line = TSHighlighter._on_line,
  _on_spell_nav = TSHighlighter._on_spell_nav,
})

return TSHighlighter