patch 8.2.1502: Vim9: can use += with a :let command at script level Commit: https://github.com/vim/vim/commit/122616d9c1b57f1e1f29f1151f8e26d24df9092a Author: Bram Moolenaar <Bram@vim.org> Date: Fri Aug 21 21:32:50 2020 +0200 patch 8.2.1502: Vim9: can use += with a :let command at script level Problem: Vim9: can use += with a :let command at script level. Solution: Give an error.

" Vim indent file
" Language:	Vroom (vim testing and executable documentation)
" Maintainer:	David Barnett (https://github.com/google/vim-ft-vroom)
" Last Change:	2014 Jul 23

if exists('b:did_indent')
  finish
endif
let b:did_indent = 1

let s:cpo_save = &cpo
set cpo-=C


let b:undo_indent = 'setlocal autoindent<'

setlocal autoindent


let &cpo = s:cpo_save
unlet s:cpo_save