Quick and dirty neovim autocmd to add or remove the wrapping parenthesis around golang multi returns whenever they go from single return to multireturn

wrap_golang_multiline_return.lua

local function wrap_golang_multi_return()
  -- If its not a go buffer dont bother doing any more work
  if vim.bo.filetype ~= "go" then
    return
  end

  local cursor_pos = vim.api.nvim_win_get_cursor(0)
  local line_num, line_col = cursor_pos[1], cursor_pos[2]
  local curr_buf = vim.api.nvim_get_current_buf()

  local line = vim.api.nvim_buf_get_lines(curr_buf, line_num - 1, line_num, false)[1]

  local P, R, S, C, Cs = vim.lpeg.P, vim.lpeg.R, vim.lpeg.S, vim.lpeg.C, vim.lpeg.Cs

  local letter = R("az", "AZ") + S("_")
  local digit = R("09")

  local whitespace = S(" \t\n")
  local repeat_whitespace = whitespace ^ 0

  local alphanumeric = letter + digit
  local identifier = alphanumeric ^ 1
  local symbol = S("., &*-[]|")

  local open_paren = P("(")
  local close_paren = P(")")
  local open_bracket = P("[")
  local close_bracket = P("]")
  local open_brace = P("{")
  local close_brace = P("}")

  local func_keyword = P("func")

  local arguments = alphanumeric + symbol + whitespace

  local function_argument_list = open_paren * arguments ^ 0 * close_paren

  -- We are just gonna ignore that nested generics happen
  local generic_argument_list = open_bracket * (arguments - close_bracket) ^ 0 * close_bracket

  local reciever = open_paren
    * alphanumeric ^ 1
    * repeat_whitespace
    * P("*") ^ -1
    * identifier
    * repeat_whitespace
    * close_paren
  --
  -- The signature can be malformed, in fact it likely as this happens while we are typing
  local return_signature = open_paren ^ 0 * (identifier + symbol) ^ 1 * close_paren ^ 0

  local return_signature_capture = vim.lpeg.Cs((return_signature / function(match)
    if match == nil then
      return
    end

    local function gsub(s, patt, repl)
      patt = vim.lpeg.P(patt)
      patt = vim.lpeg.Cs((patt / repl + 1) ^ 0)
      return vim.lpeg.match(patt, s)
    end

    -- Strip the parens off, we will add them back if we need to
    local value = gsub(match, "(", "")
    value = gsub(value, ")", "")

    -- Disable the type error, lpeg match will work as a string
    ---@diagnostic disable-next-line: param-type-mismatch
    local returns = vim.split(value, ",")
    if #returns == 1 then
      --line_col = line_col - 1
      return value
    else
      --line_col = line_col + 1
      return "(" .. value .. ")"
    end
  end))

  local anonymous_function = C(func_keyword * function_argument_list * repeat_whitespace)
    * return_signature_capture * C(repeat_whitespace * open_brace ^ 0 * repeat_whitespace)
  local named_function = C(
    func_keyword
      * repeat_whitespace
      * reciever ^ 0
      * repeat_whitespace
      * identifier
      * generic_argument_list ^ 0
      * repeat_whitespace
      * function_argument_list
      * repeat_whitespace
  ) * return_signature_capture * C(repeat_whitespace * open_brace ^ 0 * repeat_whitespace)
  local full_function = anonymous_function + named_function

  -- We want to ignore the start of the line incase it is a lambda
  local full_line = Cs(((P(1) - func_keyword) ^ 0 * full_function))

  local match = vim.lpeg.match(full_line, line)

  if match == nil then
    return
  end

  -- Disable the type error, lpeg match will work as a string
  ---@diagnostic disable-next-line: param-type-mismatch
  vim.api.nvim_set_current_line(match)

  -- When we add parenthesis we need to bump the cursor one block to the right to account for the paren on the left.
  -- we bump the column number in the match handler and execute it here
  vim.api.nvim_win_set_cursor(0, { line_num, line_col })
end

vim.api.nvim_create_autocmd(
  { "TextChanged", "TextChangedI" },
  { callback = wrap_golang_multi_return }
)