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:	C++
" Maintainer:	Bram Moolenaar <Bram@vim.org>
" Last Change:	2008 Nov 29

" Only load this indent file when no other was loaded.
if exists("b:did_indent")
   finish
endif
let b:did_indent = 1

" C++ indenting is built-in, thus this is very simple
setlocal cindent

let b:undo_indent = "setl cin<"