patch 8.2.3423: Vim9: list += list creates a new list in :def function Commit: https://github.com/vim/vim/commit/07802044b90b2cbcc64b2dfe235f019d7c37589c Author: Bram Moolenaar <Bram@vim.org> Date: Thu Sep 9 23:01:14 2021 +0200 patch 8.2.3423: Vim9: list += list creates a new list in :def function Problem: Vim9: list += list creates a new list in :def function. Solution: Append to the existing list.

Tests for complicated + argument to :edit command

STARTTEST
:$-1w! Xfile1
:$w! Xfile2
:edit +1|s/|/PIPE/|w Xfile1| e Xfile2|1 | s/\//SLASH/|w
:w! test.out
:e Xfile1
:w >> test.out
:qa!
ENDTEST

The result should be in Xfile1: "fooPIPEbar", in Xfile2: "fooSLASHbar"
foo|bar
foo/bar