neovim/runtime/lua/vim/treesitter/language.lua

local a = vim.api

local M = {}

--- Asserts that the provided language is installed, and optionally provide a path for the parser
---
--- Parsers are searched in the `parser` runtime directory.
---
---@param lang The language the parser should parse
---@param path Optional path the parser is located at
---@param silent Don't throw an error if language not found
function M.require_language(lang, path, silent)
  if vim._ts_has_language(lang) then
    return true
  end
  if path == nil then
    local fname = 'parser/' .. lang .. '.*'
    local paths = a.nvim_get_runtime_file(fname, false)
    if #paths == 0 then
      if silent then
        return false
      end

      -- TODO(bfredl): help tag?
      error("no parser for '"..lang.."' language, see :help treesitter-parsers")
    end
    path = paths[1]
  end

  if silent then
    return pcall(function() vim._ts_add_language(path, lang) end)
  else
    vim._ts_add_language(path, lang)
  end

  return true
end

--- Inspects the provided language.
---
--- Inspecting provides some useful information on the language like node names, ...
---
---@param lang The language.
function M.inspect_language(lang)
  M.require_language(lang)
  return vim._ts_inspect_language(lang)
end

return M