Vim not setting t_Co after iTerm2 update

Question

Follow up to this question - I've narrowed the issue down to the fact that set t_Co=16 in ~/.vimrc is not being applied.

SO post on restricting vim to 16 colors.

If I open vim and execute :echo &t_Co, value is set to 256. If I then manually execute :source ~/.vimrc, then :echo &t_Co again, I see the desired value of 16.

I've removed every plugin in my config to see if that was causing the issue but it persists anyway. Below are relevant .vimrc settings - this is the very end of the file:

set notermguicolors
set t_Co=16
syntax on

highlight clear CursorLine
highlight clear Todo
highlight signcolumn ctermbg=8
highlight statuslinenc ctermbg=3 ctermfg=8
highlight matchparen ctermbg=1 ctermfg=7
highlight diffchange ctermbg=0
highlight difftext ctermfg=8

I don't see any references to t_Co when inspecting via vim -V either. FWIW this issue started happening only after a recent iTerm2 and MacOS update. I've tried putting t_Co before syntax on, after it, before notermguicolors, after it, at the beginning of the file, at the end of the file. I presume something is happening during startup outside of .vimrc that does not happen again when I manually :source ~/.vimrc, but not sure where to look next.

I could set iTerm2 to an ansi terminal to limit colors that way but that was messing up other stuff. I would like t_Co to dictate available colors in vim, and to be applied on startup.

Potentially related SO post

Setting t_Co to 256 while leaving term to its Vim-defined value — or, more generally, setting t_Co and/or term to values that don't match with the host terminal — makes no sense and will likely create troubles when Vim sends a signal that is not understood by the terminal or vice-versa.

Thanks!

Answer 1

This is an attempt to help you solve your problem, not an attempt to solve it. I don't think this place is the right place for this.

So…

• I use Terminal.app with xterm-256color as $TERM, where Vim behaves as expected.

• I just installed the latest stable release of iTerm.app (3.5.1), which has xterm-256color set by default and I can confirm that:

  • doing :echo &t_Co in Vim prints 256 despite having set t_Co=16 in $MYVIMRC,
  • doing :echo &t_Co after manually sourcing $MYVIMRC effectively prints 16.

• Following a hunch, I compared the output of $ infocmp in Terminal.app and iTerm.app, which was quite interesting. The built-in one is quite different from the system one:

  1c1
  < #   Reconstructed via infocmp from file: /opt/local/share/terminfo/78/xterm-256color
  ---
  > #   Reconstructed via infocmp from file: /private/var/folders/q4/8ckdmdb136z10l1nh7ss_hsw0000gn/T/AppTranslocation/9530E85E-6C12-4995-A7A5-0592242AA0BC/d/iTerm.app/Contents/Resources/terminfo/78/xterm-256color
  4c4
  <     colors#0x100, cols#80, it#8, lines#24, pairs#0x10000,
  ---
  >     colors#0x100, cols#80, it#8, lines#24, pairs#0x7fff,
  20,21c20,21
  <     ka3=\EOy, kb2=\EOu, kbeg=\EOE, kbs=^H, kc1=\EOq, kc3=\EOs,
  <     kcbt=\E[Z, kcub1=\EOD, kcud1=\EOB, kcuf1=\EOC, kcuu1=\EOA,
  ---
  >     ka3=\EOy, kb2=\EOu, kbs=^H, kc1=\EOq, kc3=\EOs, kcbt=\E[Z,
  >     kcub1=\EOD, kcud1=\EOB, kcuf1=\EOC, kcuu1=\EOA,
  40c40
  <     kind=\E[1;2B, kmous=\E[<, knp=\E[6~, kpp=\E[5~,
  ---
  >     kind=\E[1;2B, kmous=\E[M, knp=\E[6~, kpp=\E[5~,
  42,46c42,46
  <     memu=\Em, mgc=\E[?69l, nel=\EE, oc=\E]104\007,
  <     op=\E[39;49m, rc=\E8, rep=%p1%c\E[%p2%{1}%-%db,
  <     rev=\E[7m, ri=\EM, rin=\E[%p1%dT, ritm=\E[23m, rmacs=\E(B,
  <     rmam=\E[?7l, rmcup=\E[?1049l\E[23;0;0t, rmir=\E[4l,
  <     rmkx=\E[?1l\E>, rmm=\E[?1034l, rmso=\E[27m, rmul=\E[24m,
  ---
  >     memu=\Em, mgc=\E[?69la, oc=\E]104\007, op=\E[39;49m,
  >     rc=\E8, rep=%p1%c\E[%p2%{1}%-%db, rev=\E[7m, ri=\EM,
  >     rin=\E[%p1%dT, ritm=\E[23m, rmacs=\E(B, rmam=\E[?7l,
  >     rmcup=\E[?1049l\E[23;0;0t, rmir=\E[4l, rmkx=\E[?1l\E>,
  >     rmm=\E[?1034l, rmso=\E[27m, rmul=\E[24m,
  48,49c48,51
  <     setab=\E[%?%p1%{8}%<%t4%p1%d%e%p1%{16}%<%t10%p1%{8}%-%d%e48;5;%p1%d%;m,
  <     setaf=\E[%?%p1%{8}%<%t3%p1%d%e%p1%{16}%<%t9%p1%{8}%-%d%e38;5;%p1%d%;m,
  ---
  >     setab=\E[%?%p1%{8}%<%t4%p1%d%e%p1%{16}%<%t10%p1%{8}%-%d%e48:5:%p1%d%;m,
  >     setaf=\E[%?%p1%{8}%<%t3%p1%d%e%p1%{16}%<%t9%p1%{8}%-%d%e38:5:%p1%d%;m,
  >     setb=\E[4%?%p1%{1}%=%t4%e%p1%{3}%=%t6%e%p1%{4}%=%t1%e%p1%{6}%=%t3%e%p1%d%;m,
  >     setf=\E[3%?%p1%{1}%=%t4%e%p1%{3}%=%t6%e%p1%{4}%=%t1%e%p1%{6}%=%t3%e%p1%d%;m,
  52,54c54
  <     smcup=\E[?1049h\E[22;0;0t, smglp=\E[?69h\E[%i%p1%ds,
  <     smglr=\E[?69h\E[%i%p1%d;%p2%ds,
  <     smgrp=\E[?69h\E[%i;%p1%ds, smir=\E[4h, smkx=\E[?1h\E=,
  ---
  >     smcup=\E[?1049h\E[22;0;0t, smir=\E[4h, smkx=\E[?1h\E=,
  

• I disabled the "Set $TERMINFO_DIRS…" option from the "Advanced" tab so that iTerm.app uses the same xterm-256color as Terminal.app but it didn't change the observed behavior.

• It looks like something else than the $TERM in iTerm.app is causing Vim to either ignore the set t_Co=16 in your vimrc or overrides it somehow. FWIW, I tried to play with other color-related options in iTerm.app without luck.

You should head off to Vim's issue tracker.

Good luck.

---

Here is a quick workaround until the problem is sorted upstream:

" before your highlight commands
autocmd! ColorScheme default set t_Co=16
colorscheme default

where we:

1. add an autocommand that is triggered when we explicitly tell Vim to use the default colorscheme,
2. use that autocommand to set t_Co=16,
3. tell Vim to use the default colorscheme.