Vim, tmux, and xterm-bracketed-paste

Question

From Terminal.app on my Mac, I SSH in to a box where I run Vim 8.0.1601. Left at that, everything works fine. But if I launch Vim from within a tmux window, go to insert mode, and then attempt to paste text from my Mac's clipboard into the terminal window, autoindent breaks the formatting.

If I place this on my Mac's clipboard...

Level 1
    Level 2
    Level 2
Level 1

...and then paste it into Vim running in tmux, I get this...

Level 1
    Level 2
        Level 2
        Level 1

Which is all wrong.

Now the standard solution to this problem is to use "paste mode" as described here:

https://stackoverflow.com/questions/2514445/turning-off-auto-indent-when-pasting-text-into-vim

However, I shouldn't have to do this because Terminal.app supports bracketed paste mode (described here: https://cirw.in/blog/bracketed-paste), and so does Vim. And I can confirm bracketed paste mode results in the correct paste behavior without my having to manually invoke paste mode—at least it works if I don't run tmux.

Without running tmux I see $TERM is set to xterm-256color, which matches Terminal.app's declaration.

From within tmux I can see $TERM is set to "screen-256color". From within tmux, if I override $TERM (I run "export TERM=xterm-256color") and then run Vim, bracketed paste mode works, and my pastes from my Mac are once again correctly indented. But this is a hack, and I don't know what unintended side effects I'm signing up for by spoofing $TERM.

Vim seem to look for "xterm-256color" in $TERM so it knows it is safe to offer bracketed paste mode. But in the case of tmux, it seems to be safe anyway. tmux just doesn't present to Vim a $TERM of "xterm-256color".

There are plugins and .vimrc configurations that address this (see https://coderwall.com/p/if9mda/automatically-set-paste-mode-in-vim-when-pasting-in-insert-mode). But it doesn't seem like one should have to do any of this given that Vim already implements the functionality natively.

Am I missing the "correct" way to make this work?

Answer 1

I have this in my .vimrc, which works when running tmux in gnome-terminal

if &term =~ '^tmux'
  let &t_BE="\<Esc>[?2004h"
  let &t_BD="\<Esc>[?2004l"
  let &t_PS="\<Esc>[200~"
  let &t_PE="\<Esc>[201~"
endif

Terminal in tmux is set to tmux-256color; fragment from ~/.tmux.conf:

set -g default-terminal tmux-256color