Switch on COLORFGBG to get background lightness

Now that this environment variable is kept and updated in tmux after
54553ae, we should be able to either configure terminals or explicitly
set it during startup if we want to use lighter terminals.

I'm much more comfortable with this than simply hardcoding it in the
configuration.

This doesn't solve the problem of carrying the environment variable over
an SSH session, however, but I'm not really sure there's a solution to
that besides configuring sshd(8) itself to accept these variables in
transit.

1 files changed, 26 insertions, 3 deletions

diff --git a/vim/config/syntax.vim b/vim/config/syntax.vim
index af332ba3..250ce924 100644
--- a/vim/config/syntax.vim
+++ b/vim/config/syntax.vim
@@ -5,8 +5,31 @@ if has('syntax')
   silent! syntax enable
   silent! syntax sync minlines=100
 
-  " I almost always use a dark background, so use that version of the selected
-  " colorscheme
-  set background=dark
+  " Invert Vim's built-in logic for choosing dark or light backgrounds; we'll
+  " default to choosing a dark background unless we find some reason *not* to.
+  if has('eval')
+
+    " Wrap all this logic in a function
+    function! DetectBackground()
+
+      " Split up the value of $COLORFGBG (if any) by semicolons
+      let l:colorfgbg = split($COLORFGBG, ';')
+
+      " Get the background color value, or an empty string if none
+      let l:bg = len(l:colorfgbg) ? l:colorfgbg[-1] : ''
+
+      " Choose the background setting based on this value
+      if l:bg == 'default' || l:bg == '7' || l:bg == '15'
+          set background=light
+      else
+          set background=dark
+      endif
+
+    endfunction
+
+    " Cull the function just defined directly
+    call DetectBackground()
+
+  endif
 
 endif