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")

-- These are conventions defined by nvim-treesitter, though it
-- needs to be user extensible also.
TSHighlighter.hl_map = {
    ["error"] = "Error",

-- Miscs
    ["comment"] = "Comment",
    ["punctuation.delimiter"] = "Delimiter",
    ["punctuation.bracket"] = "Delimiter",
    ["punctuation.special"] = "Delimiter",

-- Constants
    ["constant"] = "Constant",
    ["constant.builtin"] = "Special",
    ["constant.macro"] = "Define",
    ["string"] = "String",
    ["string.regex"] = "String",
    ["string.escape"] = "SpecialChar",
    ["character"] = "Character",
    ["number"] = "Number",
    ["boolean"] = "Boolean",
    ["float"] = "Float",

-- Functions
    ["function"] = "Function",
    ["function.special"] = "Function",
    ["function.builtin"] = "Special",
    ["function.macro"] = "Macro",
    ["parameter"] = "Identifier",
    ["method"] = "Function",
    ["field"] = "Identifier",
    ["property"] = "Identifier",
    ["constructor"] = "Special",

-- Keywords
    ["conditional"] = "Conditional",
    ["repeat"] = "Repeat",
    ["label"] = "Label",
    ["operator"] = "Operator",
    ["keyword"] = "Keyword",
    ["exception"] = "Exception",

    ["type"] = "Type",
    ["type.builtin"] = "Type",
    ["structure"] = "Structure",
    ["include"] = "Include",
}

local function is_highlight_name(capture_name)
  local firstc = string.sub(capture_name, 1, 1)
  return firstc ~= string.lower(firstc)
end

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

  self.hl_cache = setmetatable({}, {
    __index = function(table, capture)
      local hl = self:get_hl_from_capture(capture)
      rawset(table, capture, hl)

      return hl
    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

function TSHighlighterQuery:query()
  return self._query
end

function TSHighlighterQuery:get_hl_from_capture(capture)
  local name = self._query.captures[capture]

  if is_highlight_name(name) then
    -- From "Normal.left" only keep "Normal"
    return vim.split(name, '.', true)[1]
  else
    -- Default to false to avoid recomputing
    local hl = TSHighlighter.hl_map[name]
    return hl and a.nvim_get_hl_id_by_name(hl) or 0
  end
end

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
  }

  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

  self.tree:parse()

  return self
end

function TSHighlighter:destroy()
  if TSHighlighter.active[self.bufnr] then
    TSHighlighter.active[self.bufnr] = nil
  end
end

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

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

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

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

function TSHighlighter:get_query(lang)
  if not self._queries[lang] then
    self._queries[lang] = TSHighlighterQuery.new(lang)
  end

  return self._queries[lang]
end

local function on_line_impl(self, buf, line)
  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())

    if state.iter == nil 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 = 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]

      if hl and end_row >= line 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
                                })
      end
      if start_row > line then
        state.next_row = start_row
      end
    end
  end, true)
end

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

  on_line_impl(self, buf, line)
end

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

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;
})

return TSHighlighter